Entries in Energy System (2)

Wednesday
Sep072011

Training The Energy Systems

By Dr. Fritz Hagerman

PDF link: Training the energy system.


Dr Fritz Hagerman: Background

Dr. Fritz Hagerman, a world-renowned expert in exercise physiology, has been educating and improving rowers and coaches for over 30 years. Fritz's groundbreaking research in rowing physiology began in the late 60s with New Zealand's National team, and he has continuously worked with the U.S. National team since 1972. The results of his research have positively impacted the performance of our national teams by teaching athletes how to improve their training regimens as well as helping coaches to identify those with the best physiological potential. He has been working closely with U.S. Men's Coach Mike Teti since 1997. Fritz is a Professor of Physiology at Ohio University and also serves as the Head of FISA's Sports Medicine Commission. irow.com is extremely honored to have "THE MAN" in rowing physiology share his knowledge with us.

TRAINING THE ENERGY SYSTEMS: Part I

It was emphasized in "Defining the Energy Systems" that the interaction among the three energy systems - ATP-PC and Lactic Acid Systems (anaerobic), and the Oxygen System (aerobic) - during rowing training and competition represents several complex biochemical processes. It should, therefore, be of no surprise to any of our previous or more recent on-line viewers to learn that it is difficult to blend these three systems into an effective training program that will maximize the use and development of each system and result in improved rowing performance.

Before discussing specific recommendations to improve the effectiveness of each energy system, it is important to review the basic principles of training. Training should be mostly task specific, and when not rowing, the athlete should exercise to simulate the rowing stroke, whether in part or as a whole, including resistance or weight training.

The only exceptions would be off-season cross-training or alternative training due to an injury caused or aggravated by rowing. Overload the physiological systems, but don’t concentrate this overload; follow the 10% rule when starting a training program, meaning an increase of no more than 10% per week in training frequency, duration, and intensity. As training progresses, then the weekly increase can be reduced to as low as 5%.

Also, don’t forget that rest and recovery are vital ingredients in the best training recipe; a failure to plan for these can produce disastrous results, including peaking at the wrong time, overtraining, or chronic fatigue. Remember, under-training is usually never a problem for the motivated rower. If you are unusually tired, injured, or sick, then taking a day or two off should not be considered a serious training set-back.

Instead, abstinence of training under any of these conditions is a wise choice. Because most interruptions of training are due to respiratory infections, it is recommended that training be reduced if the respiratory problem is above the neck and cancelled if it is below the neck.

Consistency of training is one of the most important training principles; you must use it, or lose it, and as you know, it is far easier to maintain a highly trained state than to achieve one. Individualize your training program based on your skill and fitness levels, availability of training facilities and equipment, and the amount of time you have available. There is no "best time" of the day to train, as it has been shown conclusively that the body doesn’t "care" when you decide to train. However, very early morning time (1-4am) and training immediately before bedtime or following a large meal should be avoided. An increase in training should also be accompanied by an increase in the quantity and quality of food intake, a higher intake of calories will be necessary to fuel the energy systems.

Part II: Peaking

Probably the most difficult job for any coach or self-trained athlete is to design a training program that will permit “peaking” at the right time. This goal is sometimes further complicated by the need to “peak” more than once in a period of only a few months which is often the case of U.S. Olympic qualifiers.

Successful and competitive performances are dependent on carefully planned comprehensive training programs that usually span several weeks or months including up to a year or more. Periodicity of training provides planning for long-term periods (macrocycles) which, in turn, are divided into number of training sessions, days, or weeks (microcycles).

Macrocycles are often represented by an out-of-competition period, a preparation period, and a competitive period and for rowers who live north of the equator, these periods would include approximately September through December, January through April, and May through August respectively. Furthermore, training can be categorized as either specific or non-specific. Specific training includes all work done on the water, rowing ergometry, and tank exercises whereas non-specific (supplemental) training can include weight training, flexibility exercises, or any form of cross training such as cycling, swimming, running, or cross country skiing.

A well-planned training program is based on four specific training factors: type of training (specific and non-specific), frequency (number of sessions per day, week, or cycle), duration (length of time for each training session), and intensity of training (rate of doing work). The intensity of work is the most critical factor in planning a program which will culminate in your best performance. It is well known that the timing of increasing or decreasing intensity determines whether an athlete “peaks” at the desired time or not. In addition, if intensity is increased at too high a rate it can lead to overtraining, injury, and fatigue. The selection of the right mixture of the four training factors is the basis of successful conditioning.

As you train it is good advice to learn and remember how the body responds to exercise and as you plan a training schedule, record it (computer, audio, or written); don’t go on the water, enter the weight room, or sit on the ergometer without a plan. When you complete each training session, again record what you have done, compare the results with your intended plan, and immediately note how your body reacted to the training session. Modifying or changing training programs may be necessary and comparing your specific training regimens with your competitive performances over time will permit you to more objectively make accurate modifications.

Part III: The ATP-PC System

Although certain training recommendations will tend to benefit one energy system more than another, their close relationship insures an energy continuum. Despite emphasizing one energy system with a specific training stimulus, it is likely you will always have some overlap among systems, especially when you consider the variable time frames and weather conditions in which rowing, training, and competition take place.

It is also important to point out that there are a number of different ways to train each of the energy systems and a wealth of training information is now available in several different forms; video and audio tapes, the internet, live symposia, and the old stand-by, the written word. If anything, hopefully the information presented here will help you to make better and more intelligent training choices.

You may recall the description of the three energy systems available to the rowing muscles from the previous presentation on this website; the ATP-PC System, the Lactic Acid System, and the Oxygen System. With the exception of the few seconds of an exercise when our muscles must rely on the ATP-PC System for energy, the use of the other energy systems depends on the duration and intensity of the exercise.

The Adenosine Triphosphate-Phosphocreatine (ATP-PC) System

Because of only a limited contribution of this system to rowing and because it is used most effectively during the first few seconds of any exercise, it is not necessary to devote much of your training time, if any, to the improvement of this system. Our earlier research indicated that this system contributes less than 5% of the energy needed to row a highly competitive 2000m race.

Recent research seems to tell us that insignificant changes occur in this system despite regular performance of high intensity bouts of exercise that last between 5 and 15 seconds. If you want to train the ATP-PC System, it is suggested that multiple intermittent work bouts of less than 20 seconds be performed, e.g., racing starts, with recovery periods of 40-60 seconds between each work bout. In this way the work bouts are too brief to provide much stimulation to anaerobic glycolysis (Lactic Acid System), and the relative long recovery periods permit adequate restoration of ATP and PC. This also means less lactic acid is produced, thus lowering the prospect of acute fatigue associated with this by-product of anaerobic metabolism. Training at or greater than 100% of maximum effort (see accompanying training intensity table) will stimulate this energy system.

Although some athletes appear to be blessed with more powerful ATP-PC systems, the quickness and explosiveness of a rower are also determined by other factors such as muscle fibre type distribution and complex neuromuscular relationships. There is no difference in the biochemical machinery of this system between men and women, however, men tend to have higher absolute energy outputs because of their larger skeletal muscle mass. To suggest that a rower cannot get faster or react more quickly, with training, is incorrect, but it would be more productive to concentrate on developing skill and technique at higher velocities than attempting to design training sessions concentrating solely on improvement of the ATP-PC System.

It is interesting to note that probably the most widely used ergogenic aid in sports today is phosphocreatine (PC). This compound has gained popularity because it is not found as part of any sports federation banned or illegal substance list, it is suggested to be effective in improving performance, and, at least for now, there appears to be no known acute or chronic side effects. If PC is effective, then it would be for only short periods. A recent avalanche of reports concerning PC has tumbled out of both the scientific and non-scientific communities, and the results are equivocal.

Although short bouts of repetitive muscular efforts have been shown to improve using isolated muscle groups as a result of PC ingestion, sports performances following PC use, both actual and simulated, are less impressive. There seems to be a strong relationship between the amount of PC stored in the working muscle and the ability to perform repetitive anaerobic work bouts, but it is difficult to assess the PC storage capacity or content of muscle and this capacity and content apparently vary from one individual to the next. PC may be similar to our electrolyte use; if we are low in calcium then exercise performance may be impaired.

However, it would be unwise to simply consume large amounts of calcium without knowing what its concentration is in the body; calcium is relatively easy to measure in the body, PC is not. There are also no reports of the long-term effects of PC use and it will be some time before these data are available. Although the distributors of PC are recommending that all sports will benefit from its use, there is no reliable evidence that this is the case and nor is there valid evidence that increased muscular concentrations of PC spare or delay the use of the other energy systems, thus contributing to a possible larger and more efficient energy pool.

Part IV: Anaerobic Glycolysis – Lactic Acid System (LAS)

Although this energy system accounts for only about 15 to 20% of the energy contribution during a 2000m race, the timing of its contribution is critical. Because elite rowers generate their highest power outputs in the first 500m of a race, significant amounts of lactic acid are produced during the first 90 seconds. In fact, our research has shown that blood lactate concentrations reach maximal levels within the first 2 minutes of a 2000m race.

Therefore, the rower usually tolerates a very high lactate load for an additional 3-4 minutes until the sprint, when the Lactic Acid System is once again challenged to make a significant energy contribution. Venous blood lactate values in excess of 20 mmol/L of blood have been observed for elite rowers following 2000m competitive efforts and, when compared with responses of elite aerobic athletes in other sports, the rower’s responses have been among the highest. As a result, one can appreciate the physical discomfort a rower experiences during and immediately following a race.

It is important to note that measuring blood lactate does not reflect the total amount of lactate produced by the working muscles. Instead it is more of a residual concentration of lactate left over following a complex series of biochemical cellular reactions that involve lactate production, transport, clearance, buffering and resynthesis to ATP and glycogen. Maximal lactate concentrations are quite variable among individuals, but tend to be more consistent following sub maximal efforts. The Lactic Acid System’s (LAS) range of maximum energy production is 60-90 seconds during high intensity exercise.

Although there are several training schemes designed to improve this energy system, it is recommended that any training intensity above anaerobic threshold (AT) will improve the LA System (see intensity table). There is also evidence to indicate that this system, among the three energy systems, probably has the greatest capacity to change with training. Repeated rowing efforts of 1-3 minutes above AT and using a work: recovery ratio 1:3 or 1:2 will permit sufficient time for large amounts of lactate to be cleared and resysnthesized.

In other words, if you row 3 minutes, then your recovery time between exercise bouts will double or triple the exercise time. This is not only an effective way to train the Lactic Acid System, but if exercise duration is extended, the cardiovascular transport system will also greatly benefit. Any work performed at or above AT will teach the athlete lactate tolerance and, as the exercise increases in intensity, so will the learning effect. The AT seems as receptive to change as the LAS.

It is not uncommon for an elite rower to improve AT from 70-75% of maximal heart rate during the off-season to 85-90% during the competitive period. Anaerobic Threshold training should include a work: recovery ratio of 1:1. Because training intensities above AT are almost totally dependent on glucose and glycogen for fuel, it is recommended that 36- 48 hours should separate any of these higher intensity workouts. Even a diet high in carbohydrate will be challenged to replenish muscle glycogen stores during these recovery times. I have often referred to AT as that point during high intensity exercise where an untrained person will stop exercising and where a trained athlete will begin to think about quitting; the latter being precisely the state of mind you want your opponent to be in with 250-500m to go in the race.

Part V: The Oxygen System

The Oxygen System, or aerobic metabolism, makes the most significant contribution of energy during a 2000m race and also for most training rows. Although more active biochemical changes seem to occur in the muscle cell as a result of aerobic training compared to only minimal changes attributed to anaerobic training, the actual increase in VO2 max is proportionally less than measurable responses of anaerobic factors due to specific training methods. Although it appears that VO2 max is primarily determined by hereditary factors, it can be significantly improved with training. However, its capacity for change is considerably less than the potential for change in the anaerobic response.

For many years, exercise scientists have suggested that VO2 max is the single most limiting factor in performing high intensity aerobic work that extends beyond 3 minutes. Although there is a strong relationship between VO2 max and a rower’s performance, our more recent research has shown that there is an even stronger relationship between a rower’s ability to work for 5-7 minutes at a higher percentage of their VO2 max and their performance.

The most revealing physiological response to predict rowing performance at the international level is the rower’s ability to maintain their metabolic rate at or above AT. Any aerobic athlete who can significantly elevate their AT can perform high intensity exercise more efficiently (aerobic metabolism means more ATP molecules) and the by-products of the O2 system, CO2 and H2O, are easy to deal with. This is not the case when anaerobic metabolism dominates.

Oxygen, or aerobic training, can be divided into either high intensity or low intensity workouts and both can use either continuous or intermittent training sessions. High intensity aerobic training seems more conducive to intermittent work, which should range from about 75-90% of maximal heart rate (see table of training intensities) with a work recovery ratio of either 1:0.5 or 1:0.25. In other words, if you row 10 minutes in this intensity range, your recovery period should range from 2.5 to 5 minutes. The high intensity form should not only represent the majority of your aerobic training but should also be the largest contributor to total training time.

Most low intensity aerobic training should be continuous and, if done intermittently, it should not be for any length of time less than 10 minutes. Rest or recovery periods for low intensity aerobic rowing should range between 30-60 seconds; the shorter the duration of exercise, the shorter the recovery period needed. Low intensity aerobic training is often referred to as “conversational” pace and thus you should be able to talk easily during an exercise of this intensity.

Although both forms of aerobic training permit a rower to reach and maintain an aerobic base, do not interpret the value of aerobic training in only quantitative terms. Every workout, even of a low intensity, must always stress quality, and as the physical condition of the rower improves, both exercise intensity and skill level need to be elevated. Many coaches and athletes are convinced that 60-120 minutes of continuous low intensity or steady-state rowing is an important part of developing and maintaining an adequate aerobic base. We have convincing data, including muscle biopsy histochemical and biochemincal indicators, which support that rowing continuously at a low steady state intensity for 60 minutes or longer for any calibre of rower, is not more effective in maintaining aerobic capacity than 30 minutes of rowing at the same work intensity.

Not only do these results apply to a single bout of rowing, but also to 5, 10, 15, and 20 week training responses after the aerobically-trained subjects had completed a total of 20, 40, 60 and 80 training sessions respectively. Furthermore, performing 2 intermittent 30 minute exercise bouts of relatively high aerobic work intensity (10-20 % more average power than for the low intensity work) with a 7-10 minute recovery period between the 30 minute work bouts is a much stronger aerobic training stimulus than lower intensity continuous rowing.

This higher work intensity for continuous rowing could not be tolerated by most subjects for more than 32-36 minutes and still maintain a steady-state. The increased energy expenditure of the intermittent high intensity work not only proved significantly more effective than either 30 or 60 minutes of rowing in the improvement of aerobic capacity, but it was also more neuromuscularly task specific.

Comparative videotape, coaching evaluations, and metabolic data confirmed those rowers performing intermittent high intensity training bouts rowed more efficiently at all exercise intensities than those rowers who trained for longer time periods and at lower intensities, especially as stroke rating and power output increased to beyond AT, including maximum power output.

This presentation has discussed training of all three basic energy systems, including AT training with supporting research data to validate my recommendations. Regardless of your present skill level or physical conditioning state or your competitive aspirations, optimal training of the energy systems requires a comprehensive training program. In future irow.com presentations, the importance of comprehensiveness will be emphasized by discussions dealing with such topics as resistance training, cross training, artificial and actual altitude training, restricted breathing training, high oxygen training, ionization training, electrical stimulation of muscle, and muscle and blood boosting using creatine, human growth hormone, erythropoietin (EPO), and oxygen “kickers” such as flurocarbons, oxygen breathing, and oxygenated water.


Thursday
Aug112011

Training for intense exercise performance: high-intensity or high-volume training?

By: Paul B. Laursen
From: Team Danmark
Article Link: High-intensity and high volume training


Abstract

Performance in intense exercise events, such as Olympic rowing, kayak, track running and track cycling events, involves a mix of energy system contributions from aerobic and anaerobic sources. Aerobic energy supply however dominates the total energy requirements of these events after ~75 s of near maximal effort. As the aerobic energy system has the greatest potential for improvement with training, and intense exercise events generally persist for longer than 75 s, training methods for these events are generally aimed at increasing aerobic metabolic capacity. A short-term period (2-4 wk) of high-intensity interval training (HIT; consisting of repeated exercise bouts ranging in intensity from 80-175% of peak power) can elicit increases in intense exercise performance of 2-4% in well trained athletes. While the influence of high volume training (HVT) is less discussed, its importance should not be downplayed, as it may develop the aerobic base needed to support recovery and adaptation from HIT by promoting autonomic balance and athlete health. Indeed, when HIT is performed without a background of HVT, performance can be maintained, but is generally not improved. While the aerobic metabolic adaptations that occur with HVT and HIT are similar, the molecular events that signal for these adaptations may be different. The high levels of intramuscular calcium associated with HVT may signal for metabolic adaptations that improve muscle efficiency through the calcium-calmodulin pathway, while the brief low energy state created with HIT may elicit its effects through the adenosine monophosphate kinase pathway. These distinct molecular signaling pathways, which have similar downstream targets (i.e., mitochondrial biogenesis), may help to explain the potent effect that combined HVT and HIT has on aerobic energy system upregulation and intense exercise performance.

Introduction

Both high-intensity (short duration) training and low intensity (long duration) high volume training are important components of training programs for athletes who compete successfully in intense exercise events. In the context of this review, an intense exercise event is considered to be one lasting between 1 to 8 min, where there is a mix of adenosine triphosphate (ATP)-derived energy from both aerobic and anaerobic energy systems. Examples of such intense exercise events include individual sports such as Olympic rowing, kayak and canoe events, running events up to 3000 m, and track cycling events.

Exercise training, in a variety of forms, is known to improve the energy status of working muscle, subsequently resulting in the ability to maintain higher muscle force outputs for longer periods of time. While both high volume and high-intensity training are important components of an athlete’s training program, it is still unclear how to best manipulate these components in order to achieve optimal intense exercise performance in well trained athletes. While a short-term period of high-intensity training is known to improve performance in these athletes (Laursen & Jenkins 2002), it is also clear that high training volumes are of equal importance (Fiskerstrand & Seiler 2004). More recent work by exercise scientists is revealing how the combination of these distinctly different forms of training may work to optimize development of the aerobic muscle phenotype and enhance intense exercise performance.

The purpose of this discourse is to i) review the energy system contribution to intense exercise performance, ii) examine the effect of high-intensity training and high volume training on performance and physiological factors, iii) assess some of the molecular events that have been implicated in signaling for these important metabolic adaptations and iv) make recommendations, based on this information, for the structuring of training programs to improve intense exercise performance. 

Energy system contribution to intense exercise performance – what is it we are trying to enhance?

Intense exercise events involve a near maximal energy supply for a sustained period of time. These near-maximal efforts require a mix of anaerobic and aerobic energy provision. To illustrate this, Duffield et al. (2004; 2005a; 2005b) examined the aerobic and anaerobic energy system contributions to 100, 200, 400, 800, 1500 and 3000 m track running in well trained runners. The data from the male runners in these studies are plotted in Figure 1, revealing that the energy contribution to an intense exercise event arises from a mix of aerobic and anaerobic sources. The crossover point, where aerobic and anaerobic energy contributes equally, occurs approximately at 600 m of near maximal running. This compares well with an earlier crossover estimate made by Gastin (2001) of about 75 s of near-maximal exercise. Thus, for an intense exercise event that lasts beyond 75 s, total energy output is mostly aerobically driven. This is a convenient situation for the exercise conditioner, because the aerobic energy system appears to be a more malleable system to adjust. Indeed, both high-intensity and high-volume training can elicit improvements in aerobic power and capacity.

Effect of training on physiological variables and intense exercise performance

The purpose of exercise training is to alter physiological systems in such a way that physical work capacity is enhanced through improved homeostasis preservation during subsequent exercise sessions. Manipulation of the intensity and duration of work and rest intervals changes the relative demands on particular metabolic pathways within muscle cells, as well as oxygen delivery to muscle. In response, changes occur in both central and peripheral metabolic systems, including improved cardiovascular dynamics (Buchheit et al. 2009), neural recruitment patterns (Enoka & Duchateau 2008), muscle bioenergetics (Hawley 2002), as well as enhanced morphological (Zierath & Hawley 2004), metabolic-substrate (Hawley 2002) and skeletal muscle acid-base status (Hawley & Stepto 2001). The rate at which these adaptations occur is variable (Vollaard et al. 2009), but appears to depend on the volume, intensity and frequency of the training. Importantly, development of the physiological capacities witnessed in elite athletes do not occur quickly, and may take many years of high training loads before peak levels are reached.

Training can be structured in an infinite number of ways, but in general, coaches tend to prescribe periods of prolonged submaximal or shorter high-intensity exercise sessions. Submaximal endurance training performed for long durations, involves predominantly slow twitch motor unit recruitment, while higher intensity training (usually completed as high-intensity interval training) will recruit additional fast twitch motor units for relatively short durations. Both forms of training are important for enhancing the aforementioned physiological systems and intense exercise performance, but the degree and rate at which these variables change in the short term appears to be affected more acutely by high-intensity training (Londeree 1997). 

Performance and physiological effects of additional training intensity

The marked influence of high-intensity training on performance and physiological factors is well known (Laursen & Jenkins 2002), but an athlete’s ability to perform this type of training may be limited. One successful method of performing higher volumes of high-intensity training is termed high-intensity interval training. High-intensity interval training is defined as repeated bouts of high-intensity exercise (i.e., from lactate threshold to ‘all-out’ supramaximal exercise intensities), interspersed with recovery periods of low intensity exercise or complete rest.

In already well trained athletes, the effect of supplementing high-intensity training on top of an already high training volume appears to be extremely effective. In well trained cyclists, high-intensity interval training, completed at a variety of intensities (i.e., 80 – 150% VO2max power output) for two to four weeks, has been shown to have a significant influence (i.e., 2-4%) on measures of intense exercise performance (i.e., time-to-fatigue at 150% of peak power output), peak power output, and 40-km time trial performance (Lindsay et al. 1996; Stepto et al. 1998; Westgarth-Taylor et al. 1997; Weston et al. 1997). In well trained middle distance runners, Smith and colleagues (1999; 2003) found improvements in 3000 m running performance when runners performed high-intensity interval training (8 x ~2-3 min at VO2max running speed, 2:1 work to rest ratio) twice a week for four weeks. In a retrospective study performed on elite swimmers Mujika et al. (1995) found that mean training intensity over a season was the key factor explaining performance improvements (r = 0.69, p < 0.01), but not training volume or frequency. Clearly, a short-term period of high-intensity interval training supplemented into the already high training volumes of well trained athletes can elicit improvements in both intense and prolonged exercise performance (Laursen & Jenkins 2002).

While the potent influence that a short-term dose of high-intensity interval training has on intense and prolonged endurance performance is well known, the mechanisms responsible for these performance changes with well trained individuals are not clear. For example, Weston et al. (1997) had six highly trained cyclists perform six high-intensity interval training sessions (8 x 5 min at 80% peak power output, 60s recovery) over three weeks, and showed significant improvements in intense exercise performance (time to fatigue at 150% peak power output) and 40 km time trial performance, without changes in skeletal muscle glycolytic or oxidative enzyme activities.   Thus, despite the likely high rates of carbohydrate oxidation (340 µmol.kg-1.min-1) required by these efforts (Stepto et al. 2001), this acute perturbation in energy status of working muscle did not appear to increase metabolic enzyme function in the skeletal muscle of these six cyclists (Weston et al. 1997), as would be predicted based on findings made in less trained subjects (Gibala & McGee 2008). Instead, an increase in skeletal muscle buffering capacity was reported (Weston et al. 1997). Other physiological factors that have been shown to increase in parallel with improvements in performance following the addition of high-intensity interval training to the already high training volume of the well trained athlete include improvements in the ventilatory threshold (Acevedo & Goldfarb 1989; Hoogeveen 2000), an increased ability to engage a greater volume of muscle mass (Creer et al. 2004; Lucia et al. 2000) and an increased ability to oxidize fat relative to carbohydrate (Westgarth-Taylor et al. 1997; Yeo et al. 2008).

In a recent study, Iaia et al. (2008; 2009) asked runners who were training 45km/wk to lower their training volume to only 15 km/wk for 4 weeks, and instead perform sprint training (8-12 x 30s sprints; 3-5 times/wk). After this distinct change in training, runners in the sprint training groups had maintained their 10 km run performance, VO2max, skeletal muscle oxidative enzyme activities and capillarisation compared with the 45km/wk control group (Iaia et al. 2009). However, 30-s sprint (+7%), Yo-Yo intermittent recovery test (+19%) and supramaximal running (+19-27%) performances had increased in the sprint training group (Iaia et al. 2008). This study indicates that low volume high-intensity interval training can maintain an athlete’s endurance performance and muscle oxidative potential (Iaia et al. 2009), and additionally increase intense exercise performance (Iaia et al. 2008).

High-intensity interval training has also been shown to be effective at enhancing various aspects of team sport performance. For example, Helgerud et al. (2001) showed that 8 weeks of high-intensity interval training (4 x 4 min @ 95% HRmax, 3 min recovery jog, twice per week) enhanced distance covered during a match (20%), number of sprints (100%), number of ball involvements (24%) and average work intensity during a match. More recently, Bravo et al. (2008) showed that 7 weeks of repeated sprint run training (3 x 6 maximal shuttle sprints of 40 m) was more effective at enhancing Yo-Yo intermittent recovery test performance and repeated sprint ability compared with traditional interval training (4 x 4 min running at 90-95% HRmax).

Finally, when high-intensity training can be woven into training programs using ball-specific drills or small-sided games, markers of intense exercise performance can also be enhanced, with the added benefit of simultaneously receiving skill-based training (Impellizzeri et al., 2006; Buchheit et al., 2009).

In summary, it is clear that when a period of high-intensity interval training is supplemented into the already high training volumes of well trained endurance athletes, further enhancements in both intense and prolonged endurance performance are possible. As well, lower volume high-intensity interval training can maintain endurance performance ability in already well trained endurance athletes. High-intensity interval training inserted into the training programs of team sport athletes is not only effective at enhancing markers of endurance capacity, but can also improve various aspects of game-specific performance. Nevertheless, while high-intensity training can have the aforementioned profound effects on various aspects of intense exercise performance, the importance of a high training volume background should not be overlooked.

Performance and physiological effects of additional training volume

As concluded by Costill and colleagues (1991), “it is difficult to understand how training at speeds that are markedly slower than competitive pace for 3-4 h.d-1 will prepare (an athlete) for the supramaximal efforts of competition”. Nevertheless, it is well known that athletes involved with intense exercise events perform a number of long duration, low intensity training sessions per week, resulting in high weekly training volumes. Indeed, it has been estimated that well-trained (including world-elite) athletes perform ~75% of their training at intensities below the lactate or ventilatory threshold, despite competing at much higher intensities (Seiler and Kjerland, 2006). This type of training likely contributes to the high energy status of their skeletal muscle (Yeo et al. 2008), their ability to sustain high muscular power outputs for long durations, and their ability to recover from high-intensity exercise. Relative to the number of studies showing enhancements in intense exercise performance with high-intensity interval training, there are relatively few studies documenting improvements in performance with increases in training volume. This may be due to the fact that the time-course for performance improvement with high volume training does not occur as rapidly compared with high intensity training, making investigation into its influence difficult for researchers. In one study that managed to achieve this, Costill and co-workers (1991) divided collegiate swimmers into groups that trained either once or twice a day for six weeks. As a result, one group performed twice the volume of training than the other (4,950 m.d-1 vs. 9,435 m.d-1) at similar high training intensities (95 vs. 93.5% VO2max). Despite higher levels of citrate synthase activity from the deltoid muscle shown in the group that doubled their training volume, performance times following a taper over distances ranging from 43.2 to 2743 m were not different between the groups. While this study demonstrates that a relatively acute period of high volume training (with similar high training intensities) does not appear to enhance performance, the subtle effects of low intensity high training volumes over time should be realized.

The importance of low intensity long duration training sessions has been shown in at least two studies. In one longitudinal study conducted over a six-month period, Esteve-Lanao et al. (2005) compared the influence of different amounts of intensity and volume training on running performance in eight sub-elite endurance runners (VO2max = 70.0±7.3 mL.kg.min-1).

The authors found strong relationships between time spent training at intensities below the ventilatory threshold and both 4 km (r=-0.79; P=0.06) and 10 km (r=-0.97; P=0.008) run performance (Esteve-Lanao et al. 2005). In another study, Fiskerstrand and Seiler (2004) retrospectively investigated changes in training volume, intensity and performance in 21 international medal-winning Norwegian rowers over the years from 1970 to 2001. From the 1970s to the 1990s, VO2max increased by 12% (5.8 to 6.5 L.min-1) while 6-min rowing ergometer performance increased by 10%. In parallel with these performance changes was an increase in low intensity training (i.e., blood lactate <2 mM; 30 h.wk-1 to 50 h.wk-1), or high training volume, coupled with reductions in race pace and supra-maximal intensity training (blood lactate 8-14 mM; 23 h.wk-1 to 7 h.wk-1). As a result, training volume increased by 20% over this period of time (924 to 1128 h.yr-1), as did intense exercise performance results (Fiskerstrand & Seiler 2004).

While the immediate effect of high training volumes on intense exercise performance is difficult to assess, it would appear that the insertion of these low-intensity training sessions has a positive impact on performance, despite being performed at an intensity that is markedly less than that which is specifically performed at during intense exercise competition. These relatively low intensity, high training volumes may be a crucial part of competitive training programs and may provide a platform for the specific adaptations that occur in response to the high-intensity or specific workouts. 

The important interplay between high-intensity and high-volume training

The review of studies that manipulate training intensity and volume over a short-term period reveals that successful training programs may benefit from both forms of training at particular periods within an athlete’s training program. When training does not have an appropriate blend of both high-intensity and high volume training inserted into the program, performance ability tends to stagnate. For example, Iaia et al. (2008; 2009) examined the influence of marked changes in intensity and volume training on performance and metabolic enzyme activity in endurance-trained runners. In this study, runners training 45km/wk lowered their training volume to only 15 km/wk for 4 weeks, but instead performed sprint interval training (8-12 x 30s sprints; 3-5 times/week). While markers of sprint performance were improved, 10 km run performance was only maintained, and not enhanced (Iaia et al. 2008; 2009). In a study on competitive swimmers, Faude et al. (2008) used a randomised cross-over design where swimmers performed two different 4-wk training periods, each followed by an identical taper week. One training period was characterized by a high training volume, while the other involved high intensity training; neither program involved aspects of both. The authors found no difference between the training periods for 100 m or 400 m swim performance times, or individual anaerobic thresholds (Faude et al. 2008). Clearly, a mix of both high-intensity and high volume training is important, but predominance of one form of training or the other does not seems to be as beneficial. In a study demonstrating the importance of having equal amounts of distinctly different training, Esteve-Lanao et al. (2007) divided 12 sub-elite runners into two separate groups that performed equal amounts of high-intensity training (~8.4% of training above respiratory compensation point). The difference between the groups in terms of their training however was the amount of low vs. moderate-intensity training they performed. In one group, more low-intensity training (below the ventilatory threshold; 81% vs. 12%) was performed. In the other group, more moderate-intensity training (above ventilatory threshold but below respiratory compensation point; 67 vs. 25%) was performed. While intense exercise performance was not assessed, it is interesting to note that the magnitude of the improvement in 10.4 km running performance 5 months following the intervention was significantly greater (p = 0.03) in the group that performed more low-intensity training (-157 ±13 s vs. -122 ±7 s). Admittedly, the 10.4 km test used to assess running performance falls outside of the intense exercise spectrum, but does suggest that the aerobic power and capacity of these runners was enhanced by this training scheme; a capacity identified previously in this article as critical to intense exercise performance success beyond ~75 s of all-out near maximal activity.

The synthesis of these studies reveals the importance of combining periods of both high and low intensity training into the training programs of the intense exercise athlete. Seiler and Kjerland (2006) refer to this training distribution as a polarized model, where approximately 75% of sessions are performed below the first ventilatory threshold, with 15% above the second ventilatory threshold or respiratory compensation point, and <10% performed between the first and second ventilatory thresholds. For the exercise scientist, these observations beg the question: why might the mixing of distinct high- and low-intensity training sessions be so effective at increasing the energy status of working muscle and subsequent exercise performance? 

How does it happen?  Beginning to understand molecular signaling

While the picture is far from complete, scientists have begun to make impressive inroads towards understanding how skeletal muscle adapts to varying exercise stimuli, and for an excellent review on the topic, the reader may refer to the work of Coffey and Hawley (2007). As assessed by these authors (Coffey & Hawley 2007), there appear to be at least four primary signals (along with a number of secondary messengers, redundancy and cross-talk) that can lead to an increase in mitochondrial mass and glucose transport capacity in skeletal muscle following several forms of exercise training. These include i) mechanical stretch or muscle tension, ii) an increase in reactive oxygen species that occurs when oxygen is processed through the respiratory pathways, iii) the increase in muscle calcium concentration as required for excitation-contraction coupling, and iv) the altered energy status (i.e., lower ATP concentrations) in muscle. These mechanisms and pathways are complex, with many beyond the scope of this review. For the purpose of this discourse however, the focus will be on the last two of these primary signals, which have received increased attention in recent studies.

The first of these mentioned molecular signals is the prolonged rise in intramuscular calcium, such as that which occurs during prolonged endurance exercise or high exercise training volumes. These high calcium concentrations activate a mitochondrial biogenesis messenger called the calcium–calmodulin kinases (Figure 2). Second, the altered energy status in muscle associated with reductions in ATP concentrations, such as that present during high-intensity exercise, elicits a concomitant rise in adenosine monophosphate (AMP), which activates the AMP-activated protein kinase (AMPK). With these two secondary phenotypic adaptation signals identified, it becomes apparent how different types of endurance training modes might elicit similar adaptive responses (Burgomaster et al. 2008). In support of these distinct pathways, Gibala et al. (2009) showed significant increases in AMPK immediately following four repeated 30-s ‘all-out’ sprints. This was associated 3 hours later with a two-fold increase in peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) mRNA, a transcriptional coactivator that has been described by some as the ‘master switch’ for mitochondrial biogenesis (Adhihetty et al. 2003) (Figure 2). Of note, however, is that this occurred without an increase in the calcium–calmodulin kinases (Gibala et al. 2009), which are known to be stimulated during prolonged repeated contractions (Rose et al. 2007).

With these results in mind, it becomes clear what has been known by coaches for decades; that is, with respect to prescribing training that improves performance, “there’s more than one way to skin a cat”. The high mitochondrial oxidative capacity, improved fat oxidation and glucose transport in the skeletal muscle of endurance athletes may be achieved through either high volumes of endurance training, high intensities of endurance training, or various combinations of both. Higher volumes of exercise training are likely to signal for these adaptations through the calcium–calmodulin kinases (Rose et al. 2007), while higher intensities of endurance training, which lowers ATP concentrations and raises AMP levels, appear more likely to signal for mitochondrial biogenesis through the AMP-activated protein kinase pathway (Gibala et al. 2009). As shown in Figure 2, these different signaling molecules have similar downstream targets (Baar 2006). The result is an increased capacity to generate ATP aerobically. Thus, at the molecular level it may be the blend of signals induced from combined high volume and high-intensity training that elicits either a stronger or more frequent promotion of the aerobic muscle phenotype through PGC-1α mRNA transcription (Figure 2). As well, the lower intensity higher volume training sessions are likely to promote autonomic balance by facilitating recovery and muscle remodeling based on the molecular signals received from the high-intensity training sessions.

How do we optimally structure training programs for high performing endurance athletes?

The synthesis of this information reveals a pattern highlighting the importance of applying periods of both high-intensity and high volume training at the appropriate time in a training program, in order to elicit optimal intense exercise performance. Experts in training program design refer to this art as periodisation (Issurin 2008). While the importance of the high-intensity interval training stimulus appears to be critical (Londeree 1997), the submaximal or prolonged training durations (volume of repeated muscular contractions) cannot be downplayed (Fiskerstrand & Seiler 2004). These high volume training periods likely form the aerobic base needed for the rapid recovery between high-intensity training bouts and sessions. Over time, the progressive result is likely to be an improved efficiency of skeletal muscle and a development of the fatigue resistance aerobic muscle phenotype. Indeed, development of the successful intense exercise athlete tends to require a number of years exposure to high training volumes and intensities (Schumacher et al. 2006). The low intensity high training volumes also likely promote the recovery and autonomic balance needed for the facilitation of the mitochondrial protein synthesis signaled for through the high-intensity interval training sessions. The art of successful intense exercise coaching, therefore, appears to involve the manipulation of training sessions that combine long duration low-intensity periods with phases of very high-intensity work, appropriate recovery, and tapering (Mujika et al. 2000; Issurin 2008; Pyne et al. 2009). These same principles are likely to apply for team sport athletes, although other forms of training should likely be incorporated, such as plyometric training (i.e., drop jumps and countermovement jumps), which has recently been shown to improve agility time in semiprofessional football players (Thomas et al. 2009).

The paper will finish with two practical examples that demonstrate the effectiveness of this model. The first example is New Zealand’s Olympic 800 m running legend, Sir Peter Snell. Snell was a protégé of the late New Zealand athletics coach Arthur Lydiard, who was renowned for prescribing very high training volumes to his athletes who performed intense track events. Throughout his years of training, Snell was prescribed training volumes that would replicate those performed by most marathon runners (~160 km per week, interspersed with weekly high-intensity track workouts; P Snell, personal communication). The result was an 800 m world record in 1962 (1:44.3), and winning double Gold in the 800 m and 1500 m events at the 1964 Tokyo Olympic Summer Games.

In another report of a high training volume plan that elicited a winning intense exercise performance was that of the German 4000-m team pursuit cycling world record achieved at the Sydney 2000 Olympic Games (Schumacher & Mueller 2002). In this paper, Schumacher and Mueller (2002) provide a detailed account of the training performed by the cyclists over the 7 month lead-up to the critical event. In general, training involved extremely high training volumes (29,000 – 35,000 km/yr) that included long periods of low-intensity road training (~50% VO2max) interspersed with stage racing (grand tour) events. While the road racing component of the cyclists’ training program would have entailed numerous periods of both high volume and high intensity stimuli, it wasn’t until the final 8 days prior to the Sydney Olympics that a specific high intensity training taper period on the track was prescribed. Nevertheless, this training design yielded outstanding results, and the model has since been replicated by both the Australian and British cycling teams to break this record repeatedly over the last two Olympic Games (M. Quod, Cycling Australia, Australian Institute of Sport, Personal Communication).

Summary

Our understanding of how best to manipulate the training programs of athletes competing in intense exercise events so that performance is optimised is far from complete. It would appear that a polarised approach to training is optimal, where periods of both high-intensity and low intensity but high volume training are performed. The supplementation of high-intensity training to the high volume program of the already highly trained athlete can elicit further enhancements in endurance performance, which appears to be largely due to an improved ability of the engaged skeletal muscle to generate ATP aerobically. Prolonged durations of low intensity or high volume training are likely to facilitate recovery and adaptation by promoting autonomic balance and the health of the athlete. Team sport athletes can also benefit from periods of high-intensity interval training, game-based interval training, and plyometrics. Some of the important molecular signals arising from various forms of exercise training include the AMPK and calcium-calmodulin kinases, likely to be activated in response to intense and prolonged exercise, respectively. Both of these signals have similar downstream targets in skeletal muscle that promote development of the aerobic muscle phenotype. Further understanding of how best to manipulate the training programs for future intense exercise athletes and team sportsmen will require the continued cooperation of sport scientists, coaches and athletes alike.

Consensus statements

1) Intense exercise events require a blend of anaerobic and aerobic energy, with the aerobic energy system predominating after near-maximal exercise durations of ~75 s.

2) Short term high-intensity training, typically performed as high-intensity interval training, can elicit improvements in intense exercise performance.

3) Low-intensity, long duration work, or high training volumes, are an important component of successful athletes that perform in intense exercise events, and may facilitate recovery and adaptation from high-intensity sessions by promoting autonomic balance and the health of the athlete.

4) From a metabolic perspective, high training volumes may promote development of the aerobic muscle phenotype through the CaMK signalling pathway, while high-intensity training may affect these adaptations through the AMPK signalling pathway.

5) A polarised training approach where relatively small volumes of high training intensities (~10-15%) are manipulated around large volumes of low intensity training (~75%) appears to be an effective means of enhancing intense exercise performance.

Figure captions


Figure 1. Percent aerobic and anaerobic energy system contributions to near-maximal running over distances ranging from 100 m to 3000 m. Figure derived based on the male data obtained from the studies of Duffield et al. (2004; 2005a; 2005b).

 


Figure 2. Simplified model of the adenosine monophosphate kinase (AMPK) and calcium-calmodulin kinase (CaMK) signalling pathways, as well as their similar downstream target, the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1 α). This ‘master switch’ is thought to be involved in promoting development of the aerobic muscle phenotype. High-intensity training appears more likely to signal via the AMPK pathway, while high volume training appears more likely to operate through the CaMK pathway. ATP, Adenosine Triphosphate; AMP, Adenosine Monophosphate; GLUT4, Glucose Transporter 4; [Ca2+], intramuscular calcium concentration.

Acknowledgements

Special thanks to Iñigo Mujika, Chris Abbiss, Marc Quod and Alison Hall for their helpful comments and editorial assistance during the preparation of this manuscript.

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