Can endurance running performance be predicted from cycling performance?

Topic for Summary and Critique - by Jay Chau

Contents

• Statement of the Topic
• Introduction
• Specificity of Training
• Cross-training Effect
• Factors Determining Endurance Performance
• Clinical Implications
• Conclusion
• References
• Short Answer Review Questions

Statement of the Topic

Can endurance running performance be predicted from cycling performance?

Introduction

The answer to the above question lies in two important, and, perhaps confronting concepts in the science of exercise physiology, the principle of specificity and the cross-training (cross-transfer) effects in aerobic training. It also depends on the level of training, as Tanaka (1994) believed that for highly trained athletes, the principle of specificity of training tends to have greater significance. For the general population, cross-training may be beneficial in terms of overall fitness.

The primary determinant of performance in endurance sports is the ability to produce and efficiently utilize large amounts of energy at an extraordinary fast rate for prolonged periods of time. This high rate of energy expenditure must occur with minimal alteration in homeostasis of either cardiovascular, haemodynamic, metabolic, thermal and musculoskeletal functions (O'Toole and Douglas 1995). Adaptive responses to endurance training involve central and peripheral adaptations. Central adaptations occur in the cardiovascular system, which include increased blood volume, erythrocyte production, stroke volume and maximal cardiac output. These factors increase the maximal capacity of the central circulatory system to transport oxygen. In contrast, peripheral or local adaptations enhance oxygen utilization in the exercising muscles, and are more strongly associated with the specificity of training. These adaptations occur in the metabolic systems which include increased capillary density, mitochondrial number and volume, oxidative enzyme activity and arterial-venous oxygen difference (a-v O₂ difference) (McArdle et al 1996, O'Toole and Douglas 1995, Tanaka 1994).As demonstrated in enzymatic activities, peripheral adaptations occur only in exercising skeletal muscles. Thus, training adaptation in non-exercising muscles appears to be minimal (Tanaka 1994).

There is a debate on the relative importance of central and peripheral adaptations in determining maximum oxygen uptake/capacity (VO₂max). If central adaptations are more important, any endurance training may benefit another endurance performance (cross-training). From previous studies, it appears that in normal and sedentary individuals increased systemic cardiac output (central) and a widened a-v O₂ difference (peripheral) contribute equally to an increase in VO₂max following endurance training. In trained individuals or when endurance training is prolonged over years, the increase in VO₂max is attributed almost completely to a rise in maximal stroke volume or cardiac output (Tanaka 1994).

Specificity of Training

According to the principle of specificity, exercise training should stimulate, as closely as possible, the conditions of a specific sport to elicit the greatest physiological adaptations. Therefore, one of the strongest arguments against the concept of cross-training is the principle of specificity of training. Since cross-training is a form of nonspecific training, a significant issue is whether crossover benefits of training occur from such training (Tanaka 1994). A specific exercise stress, such as strength-power training, induces specific strength-power adaptations, and a specific aerobic or cardiovascular exercises elicits specific endurance training adaptations, with only a limited interchange of benefits derived between muscular strength and aerobic training (McArdle et al 1996).

Specificity of central changes (VO₂max)

Based on available research, McArdle et al (1996) advised that during training for specific aerobic activities such as running, cycling, or rowing and swimming, the overload must both engage the appropriate muscles required by the activity and induce an exercise stress on the central cardiovascular system. Little improvement is observed when aerobic capacity (VO₂max) is measured during a different exercise, yet improvement is significant when the test exercise is the same type of exercise as that used in training. Competitive cyclists can generate higher VO₂max values than runners on a cycle ergometer, whereas highly trained runners can achieve higher VO₂max than cyclists on a treadmill running (Tanaka 1994, McArdle et al 1996). Improvements in VO₂max probably reach a peak in training, and, thereafter, improvements in performance are supported by other mechanisms only partly related to the capacity of the oxygen transport system. These adaptations most likely take place in the active musculature rather than being related to central circulatory factors (McArdle et al 1996).

Specificity of peripheral changes

In endurance training, the overload of specific muscle groups enhances work performance and aerobic power by facilitating both oxygen transport and utilization at the local level of the trained muscles (McArdle et al 1996). Although musculature used for cycling overlaps with that used during running, biomechanical analysis suggests that ranges of motion, length of muscles, type of contraction and speed of contraction can be quite different. For example, the quadriceps muscle group is extensively used in cycling, whereas plantar flexors are preferentially recruited in running. Running is a weight bearing exercise, and is characterized by substantial involvement of eccentric contractions. Also, the enzyme activities in oxidative capacity of the vastus lateralis muscle are markedly greater in competitive cyclists compared with endurance-trained runners. Such adaptations would certainly increase the capacity of the trained muscles to generate ATP aerobically (McArdle et al 1996, O'Toole and Douglas 1995, Tanaka 1994).

Cross-training Effect

In recent years, multi-event sports like biathlons and triathlons have grown in popularity, and the interest in the potential for endurance run and cycle training to complement each other has been renewed. There is abundant anecdotal evidence indicating that cross-training may be beneficial to competitive athletes, however, very few scientific studies have investigated this particular type of training (Ruby et al 1996, Tanaka 1994).

Previous research has documented the limited cardiorespiratory improvement that can transfer between running and cycling training when training in one of these exercise modes. Ruby et al (1996) commented that the majority of these investigations were designed to answer questions of training specificity in moderately to highly trained individuals, and have neglected to specifically address the cross-training concept. In their study, they found that the previously untrained females could increase treadmill running and cycle ergometer VO₂max from either running, cycling, or combined running and cycling training. These increases could be detected after five weeks of training, and show further improvement with an additional five weeks of training. Interestingly, none of the three training groups showed significant improvements in arm ergometry VO₂max during the entire 10 weeks of training, a finding indicating that central training adaptations were minimal. However, the decrease in the submaximal heart rate response during arm ergometry during the training indicated that minor central adaptations had occured. The increase in %VO₂max at the lactate threshold (LT) that was not specific to training group indicates that the overall increase in VO₂max is primarily a result of peripheral training adaptations. Unlike previous studies using either recreationally active or well-trained male athletes, Ruby et al (1996) did not demonstrate specific increase in the LT. It is likely that higher levels of endurance fitness are necessary before mode specificity in VO₂max and LT measures become pronounced. Consequently, the initial gains in aerobic adaptation to endurance exercise do not appear to have mode specificity in the untrained population, and the selection of an exercise regime need not be biased towards either running or cycling exercise.

It appears that some transfer of training effects on VO₂max exist from one mode to another. Available data generally suggest that training effects gained in running are more likely to transfer to cycling than vice versa. It was generally concluded that adaptation following cycling training is more specific than that following running training, whereas training adaptation of running training is more general in nature. Nevertheless, it should be noted that the improvements in the cycling training group never exceeded those of the running training group when measured on the treadmill, and vice versa (Tanaka 1994).

Factors Determining Endurance Performance

McArdle et al (1996) commented on the use of VO₂max as a standard to compare one's capacity for endurance exercise. Although this measurement generally relates to exercise performance, it does not fully explain success. This is because longer-duration, high-intensity exercise is not performed at VO₂max. The use of %VO₂max can represent how close to VO₂max an athlete can perform during competition. It has been suggested that endurance exercise performance is directly related to the ability to use a high fraction of VO₂max with minimal accumulation of blood lactate. The %VO₂max, sustainable in endurance events, is dependent on the race distance and the location of LT. The lactate threshold is defined as the highest exercise level or level of oxygen uptake that is not associated with an elevation in blood lactate concentration above the pre-exercise level (or an increase less than 1.0 mM). Exercise at an intensity above LT reduces endurance time due to metabolic acidosis and accelerated glycogen depletion, therefore the successful endurance athlete is often characterized by the ability to perform high amounts of work at or just below LT. The LT reflects the degree of muscular stress, glycogenolysis and fatigue, and is specific to the mode of exercise. Training-induced increases in capillary density, size and number of mitochondria, as well as the levels of various enzymes and transfer agents enhance aerobic metabolism and theoretically have the potential to alter LT. Because these adaptations occur peripherally, training to increase LT must be performed separately for each type of exercise (Coyle 95, O'Toole and Douglas 1959, Sleivert and Rowlands 1996).

Coyle (1995) further commented that it was not clear whether the blood lactate accumulation was a result of cardiovascular limitations linked to oxygen delivery, as reflected by VO₂max, as opposed to metabolic factors in the exercising muscle related to the extent to which mitochondrial respiration is disturbed to maintain a given rate of oxygen consumption. However, improvements in performance after a two to three year period of intense training are associated with improvement in blood LT, whereas VO₂max generally increases very little thereafter. Another major factor determining LT is the muscle's aerobic enzyme activity or mitochondrial respiratory capacity. The mitochondrial number sharing in the work can be increased by using more muscle fibers, provided they can be adequately perfused.

Having established that LT is the most important determinant of the energy expenditure maintained during performance, the other factor determining how well this translates into actual athletic performance velocity is the economy of movement. Efficiency of movement can be best be described as the relationship between energy input and the resultant mechanical output. A more economic athlete uses less oxygen than their less economic counterpart at a standard velocity and theoretically is able to move faster or conserve energy (Coyle 1995, O'Toole and Douglas 1995, Sleivert and Rowlands 1996). Despite the physiological and extrinsic factors like the set-up of the bicycle or the shoes of the runners, it is obvious that a trained athlete with a better technique in the specific sport would has a better biomechanical advantage in that specific athletic performance.

Clinical Implications

It has been suggested that training stress will be distributed to different muscles and overuse injuries may be prevented by performing multi-sport activities. Cross-training also has a practical implication for injured athletes (Tanaka 1994). After only on or two weeks of detraining, significant reductions in both metabolic and exercise capacity can result, and many of the training improvements are lost within several months (McArdle et al 1996). Many runners fear that a break from running (due to running-related injuries) will lead to a decrease in fitness or an increase in body weight and few are willing to endure long periods of inactivity. It has been shown that a layoff of six weeks can lead to a decrease of 14 to 16% in VO₂max. To avoid these negative effects, injured runners often seek alternative training methods (Eyestone et al 1993).

It seems reasonable to suggest that in order to reduce the side effects of detraining, an injured distance runner switch to cycling training. The cross-training effects are most evident in less elite athletes, as was shown by Eyestone et al (1993). They compared deep water running, cycling, and running training modes in maintaining VO₂max and 2-mile running performance. Over a six week period, the results showed no significant differences among the high, medium, or low performance levels in changes of the testing parameters. In addition, Wilber et al (1996) demonstrated that deep water running exercise could served as an effective training alternative to land-based running for the maintenance of physiological determinants of aerobic performance over a period of six weeks among trained distance runners. As such, these findings have important implications for injured athletes attempting to maintain high levels of aerobic conditioning during rehabilitation and for noninjuried athletes attempting to recover from musculoskeletal fatigue brought on by the stress on land running.

If the intent of training is to maintain or increase general aerobic fitness, any aerobic exercise may be appropriate. However, if training is intended to maintain or enhance athletic performance, the exercise needs to be specific and simulate the exercise motions. It is important that training volume should be adjusted when constructing a cross-training program (Tanaka 1994).

Conclusion

• The principles of specificity of training tend to have greater significance, especially for highly trained athletes. For the general population, however, cross-training may be highly beneficial in terms of overall fitness.
• Adaptive responses to endurance training involve central and peripheral adaptations. Central adaptations occur in the cardiovascular system, while peripheral adaptations enhance oxygen utilization in the exercising muscles.
• Little improvement is observed when aerobic capacity is measured during a different exercise, yet improvement is significant when the test exercise mode is the same as the exercise mode used in training.
• Improvements in VO₂max probably reach a peak in training, thereafter, improvements in performance are supported by adaptations which most likely take place in the active musculature rather than being related to central circulatory factors. Overloading of specific muscle groups facilitates both oxygen transport and utilization at the local level of the trained muscles.
• Initial gains in aerobic adaptation to endurance exercise do not appear to have mode specificity in the untrained population, and selection of an exercise regime need not be biased towards either running or cycling exercise.
• Endurance exercise performance is directly related to the ability to use a high fraction of VO²maxwith minimal accumulation of blood lactate.
• The lactate threshold is the most important determinant of the energy expenditure maintained during performance, the other factor determining how well this translates into actual athletic performance velocity is the economy of movement. Cross-training has a practical implication for injured athletes. If the intent of training is to maintain or increase general aerobic fitness, any aerobic exercise may be appropriate. However, if training is intended to maintain or enhance athletic performance, the exercise needs to be specific and stimulate the exercise mode.

References

Coyle EF (1995)

Integration of the physiological factors determining endurance performance ability. Exercise and Sport Science Review 23:25-62.

Eyestone ED, Fellingham G, George J, Fisher G (1993)

Effect of water running and cycling on maximum oxygen consumption and 2-mile run performance. American Journal of Sports Medicine 21:41-44.

McArdle WD, Katch FI and Katch VL (1996)

Exercise Physiology: Energy, Nutrition and Performance (4th ed.). Philadelphia: Lea and Febiger.

O'Toole ML and Douglas PS (1995)

Applied physiology of triathlon. Sports Medicine 19:251-267.

Ruby B, Robergs R, Leadbetter G, Mermier C, Chick T, Stark D (1996)

Cross-training between cycling and running in untrained females. Journal of Sports Medicine and Physical Fitness 36:246-254.

Sleivert GG and Rowlands DS (1996)

Physical and physiological factors associated with success in the triathlon Sports Medicine 22:8-18.

Tanaka H (1994)

Effects of cross-training. Sports Medicine 18: 350-339.

Wilber RL, Moffatt RJ, Scott BE, Lee DT, Cucuzzo NA (1996)

Influence of water run training on the maintenance of aerobic performance. Medicine and Science in Sports and Exercise 28:1056-1062.

Short Answer Review Questions

1. What are the adaptive responses to endurance training?
2. Define the meaning of specificity of aerobic training?
3. Define the term lactate threshold?
4. Can an elite cyclist advance his endurance performance by training in running? Explain.
5. What are the effects in detraining in endurance athletes?
6. What is the most important factor to determine whether there is a cross-transfer effects?

Exercise Physiology Educational Resources 1999