Can endurance running performance be predicted from cycling performance?

Proposition for Debate - by Angela Peterson

Contents

• Statement of the Topic
• Introduction
• Background Knowledge
• Required Knowledge
• New Knowledge
• Clinical Implications
• Conclusion
• References
• Short Answer Review Questions

Statement of the Topic

Can endurance running performance be predicted from cycling performance?

This question is related to the physiological principles of specificity of training, and has significant implications for exercise testing in measuring aerobic fitness. The aim of this paper is to review some of the terminology associated with the topic, identify the physiological parameters which determine endurance running performance and the methods of measurement, and discuss several studies that have investigated both the specificity of testing issue, and the specificity of training aspect to determine if the cycling performance of an athlete can predict their running endurance performance.

Introduction

The primary determinant of endurance running performance is the ability of the athlete to sustain high rates of energy expenditure for long periods of time. The most common forms of aerobic capacity testing are the treadmill (TM) and cycle ergometer (CE) test. Endurance training induces adaptive responses in the cardiorespiratory and metabolic systems of the body. There are 2 main questions relating to the specificity of the training responses on these central and peripheral systems. Firstly, can these two tests be used interchangeably for predicting the endurance response to different sports, e.g, can cycling accurately predict the endurance response to a running test? Secondly, can alternative or "cross-training" with a non-running specific sport, e.g, cycling, improve running performance? Both these factors have important clinical implications with respect to performing baseline and subsequent fitness tests on athletes to measure the effects of an aerobic training programme, and in recommending methods of cross training for maintaining or improving aerobic fitness in circumstances such as injury, and off season fitness programmes. In these situations, we need to be sure that what we are testing is accurately reflective of adaptive responses, and that the exercise we are prescribing will be of benefit to the athlete in their chosen sport. Specific comparison of other sports is beyond the scope of this paper.

Required Knowledge

Knowledge is assumed of energy metabolism, systems of energy delivery and utilisation, methods of aerobic testing and the potential hazards and skeletal muscle structure and function. Relevant sections can be found in McArdle, Katch and Katch (1996) Chapters 6, 7, 8, 15, 17 and 18.

Background Knowledge

Aerobic exercise and training, as with all forms of training is based upon the principle of "overload", that is that the exercise stimulus must be sufficient to result in adaptation of the system to the exercise. The specificity principle as it relates to aerobic activity, involves both metabolic and physiologic adaptations of the aerobic system at two levels:

1. Centrally - cardio-vascular adaptations.
2. Peripherally - local changes in the active muscles involved with the exercise

Training Adaptations

Endurance training adaptations enable alteration of the above physiological characteristics resulting in improvements in performance. The adaptations involve both central and peripheral mechanisms both of which contribute to an increase in aerobic capacity following endurance training.

Central

Central adaptations involve the cardiovascular system whose function it is to deliver oxygen and substrates to the exercising muscle . Adaptations include increased plasma volume, redirection of blood flow to the active muscles, increase in heart size, reduced heart rate (HR), increased stroke volume (SV), increased cardiac output (Q), increased total muscle blood flow during maximal exercise and reduced blood pressure . Cardiac output shows perhaps the most significant change, resulting directly from the increased stroke volume due to the enlargement of the left ventricle and it's increased volumetric capacity.

Peripheral

The peripheral adaptations of aerobic overload result in enhanced oxygen utilisation by exercising skeletal muscle due to increased capillary density, increase in the size and number of mitochondria, increased oxidative enzyme activity (resulting in increased carbohydrate oxidation), improved lipolysis (and hence fat metabolism) evidenced by an increased arterio-venous oxygen difference (a-v O₂D). Other peripheral factors that determine metabolic activity during endurance exercise are the amount of muscle mass that is involved in the work done, and the muscle fiber composition type (% Type 1 fibers - slow oxidative metabolic function).

From previous studies on normal and sedentary individuals, it appears that both central and peripheral mechanisms (increased Q and widened a-v O₂D) equally contribute to an increase in VO_{2 max}.

Methods of aerobic capacity testing

The TM and CE tests are both commonly used laboratory tests. Both are simple, cheap, use large muscle groups and require minimal familiarisation time from subjects. However, when running and cycling are analysed more closely, there are some fundamental differences. The muscle recruitment patterns, speed and timing of contractions, muscle groups emphasised (quads in cycling and plantar flexors in running), and metabolic processes are all different. Stromme (1977) advocates that training should have the effect of increasing cardiorespiratory adaptations to a greater extent in a test that makes optimal use of the specifically trained muscles, ideally testing performance of the sport, assuming large muscle groups are involved.

Endurance Performance

Endurance running performance is described as the velocity that can be maintained over a given distance, or additionally, in cycling terms, the power output maintained for a given time.

Performance is determined by several functional physiological characteristics:

VO2 max

The physiological variable that best describes the capacities of the cardiovascular and respiratory systems is generally accepted to be the VO_{2 max}. The value for the VO_{2 max} is determined by the capacity of the cardiorespiratory system to deliver oxygen to the tissues. Average values in elite long distance runners range from 75-85 ml/kg/min. In order to stress the respiratory and circulatory systems to maximal extent, large muscle groups must be utilised. For this reason the treadmill or cycle ergometer tests have been the preferred method of VO_{2 max} testing for the last 4-5 decades. Today they remain the most common method of aerobic capacity testing.

The correlation between VO_{2 max} and run performance has been reported to range between 0.36-0.96 . The variation in correlation depends largely upon how VO_{2 max} is reported, with the lowest correlations found when VO_{2 max} was expressed in L/min, the highest when expressed relative to body weight (as quoted above) . There are also a number of inherent testing hazards and error margins when considering the results of VO_{2 max} testing.

The VO_{2 max} cannot be the only predictor of performance since it has been found to reach a plateau during training, the further improvements in performance being attributed to other physiological factors.

Anaerobic Threshold

This is typically described as either the Lactate Threshold (LT). Accumulation of 4 mmol/L of lactic acid in the blood has been termed the onset of blood lactic acid (OBLA), although there is wide variation in the literature regarding the terminology and definition of the anaerobic threshold. For the purpose of this paper it will be referred to at the lactate threshold. The LT measures the degree of muscular and metabolic stress during exercise and is usually expressed as occurring at a fraction of VO_{2 max} (%VO_{2 max}).

The %VO_{2 max} that an endurance runner can maintain during a run is restricted by the accumulation of lactic acid. The VO₂ at LT is reported to be the best measure of metabolic capability for endurance exercise. Generally, during exercise above 60-75% VO_{2 max}, glycogenolysis is increased and lactate begins to accumulate exponentially in the active muscle and blood . Early studies found that marathon runners maintain a velocity in competition that corresponds with the intensity at which lactate begins to accumulate in the blood and muscle. The LT explains why runners with similar VO_{2 max} can differ in endurance performance times, those with a higher LT being capable of performances superior to those with lower LT but the same VO_{2 max}. Those with a high LT are therefore able to exercise at a higher %VO_{2 max} and thereby utilise a large fraction of their aerobic capacity (85-90%VO_{2 max}). Factors reported to be associated with a high %VO_{2 max} at LT are years of cycling experience, percentage of Type 1 muscle fibres, and duration of intense cycle training i.e, 5 or more.

Economy of Motion

Economy or efficiency of motion can best be described as the relationship between energy input and the resultant mechanical output . The individual with the greatest economy of motion consumes the least amount of oxygen . The VO₂ during sub-maximal exercise at a given movement speed is the means of quantifying economy of motion. Several studies have shown a high correlation between VO₂ and performance times in both running and cycling . The superior performances of athletes of similar VO_{2 max} and LT can be explained by economy of motion.

New Knowledge

A number of studies exist that have studied aspects of the cardiovascular specificity phenomena. Firstly, whether aerobic capacity values are the same when tested on the treadmill and the cycle ergometer, and whether specific training in one form of exercise has cross-over effects into the other.

Cross-Training

When considering the muscle groups involved in running and cycling, it would be feasible to expect some cross-training benefits due to the common muscle groups involved. However, there are fundamental differences in muscle activation within the 2 disciplines, the quadriceps being preferentially utilised during cycling, and the plantar flexors during running, as well as other biomechanical factors such as speed, force and length of contraction and body position.

In a landmark study conducted by Pechar et al (1974), the specificity of cardiorespiratory adaptation to training was studied in 60 male college students. Training involved 8 weeks of TM, CE or no training for the control group. The TM group achieved similar improvements in VO_{2 max} for both testing procedures following the training period. However in the cycle trained group, improvements in VO_{2 max} were highest in the CE test (7.8%) compared with 2.6% improvement registered on the TM. The difference between the TM and CE VO_{2 max} tests in the BE group following training were significantly less than in the TM trained group. These results strongly suggest a specificity effect for the VO_{2 max} of the BE trained group. The results also convey a strong message regarding the type of test used to evaluate cardiorespiratory adaptations to training. If only the TM test had been used to evaluate both types of training on the VO_{2 max}, the conclusion would have been that TM training produces greater improvements than BE training. If only the BE test had been used for both training groups, the conclusion would have been of equal effectiveness of both types of training for improving VO_{2 max}.

Pechar et al (1974) concluded that run training results in a general improvement in VO_{2 max}, independent of the method of testing, whereas cycle training has a specific effect which is more obvious when tested on cycling apparatus. Cycle training does, however, result in small improvements in TM VO_{2 max}.

Pierce et al (1990) studied a group of untrained, sedentary males who were trained either by running on an outdoor track or on a bicycle track. The group trained in running on an outdoor track significantly improved their LT on both the TM and CE tests, whereas the cycling group only improved the LT on the CE test. This agrees with the findings of Pechar, that running results in a more general adaptation, whereas cycling has more specific effects.

In contrast to these finding, a group of untrained females who were allocated TM, CE or training in both methods, TM and CE VO_{2 max} as well as VO₂ at LT improved throughout the 10 week training period regardless of training group . These results indicated that the aerobic effects of either run, cycle or a combination of both are similar in untrained females. This was the only study which disputed the concept of aerobic training specificity. The study used HR to measure training intensity, and given that HR is limited by the central cardiovascular system, it is questionable whether the cycle trained subjects were able to overload their peripheral, anaerobic system sufficiently to achieve a significant peripheral training adaptation.

Specificity of Local Changes

The overload of specific muscle groups results in and increase in work performance and aerobic power by facilitating oxygen transport, and increasing it's rate of utilisation at the local level of trained muscle. The %VO_{2 max} attainable is mostly governed by the anaerobic LT. The ability to alter the LT is determined by the peripheral or local musclular adaptations to endurance exercise, namely increases in capillary density.

This effect is well documented in the instance of the Vastus Lateralis muscle of cyclists that show a greater oxidative capacity, and ability to generate ATP aerobically, than the same muscle group in runners . These adaptations only occur in specifically trained muscles, and are only seen when these muscles are activated . It has been suggested that in order to optimise the specific adaptations of the local muscle, that the aerobic exercise should include muscles specific to the sport being trained eg, runners should run, and swimmers should swim.

Specificity of Cardiovascular Changes

If the exercise intensity, duration and frequency are the same, then the adaptations of the cardiovascular system are the same regardless of the type of exercise performed, as long as it involves large muscle groups, and the stimulus is sufficient to induce overload on the cardiovascular system to produce increased SV and CO.

Testing

Maximal Exercise

Hermansen and Saltin (1969) investigated the respiratory and circulatory response to maximal and sub-maximal treadmill (TM) and cycle ergometry (CE) testing, of 55 male subjects involved in varying sports who were divided into groups according to age and their training conditions. Their results showed 47 subjects had an average 7% higher VO_{2 max} during maximal running compared to the CE, and by group comparison, determined that level of fitness and type of training did not influence the results. They also noted and slight increase in CE VO_{2 max} at pedal frequencies of 60-70 rpm compared with 50 and 80rpm frequencies. They concluded that at 3 degrees inclination or more, TM running resulted in a higher VO_{2 max} than CE in non-specifically trained males. It can be concluded from this study that VO_{2 max} testing on an inclined TM will yield higher values than on a CE in a group of endurance athletes from mixed sports.This finding has been supported by many other studies since , and has been explained as being due to the larger muscle mass employed during running, and further supported by the general aerobic training response identified in run trained subjects.

Following this study, Hermansen et al (1970) investigated whether the VO_{2 max} difference between TM and CE was due to a higher SV or a-v O₂D during TM running. They used 13 male college students matched to13 male endurance trained subjects, and tested maximal and sub-maximal TM and CE. Their results agreed with their previous study, finding a 10% higher VO_{2 max} during uphill running compared with CE in both groups, determining that the increase was due to an increase in cardiac output in the TM group. This in turn was attributed to a higher SV during uphill running since the maximum HR for both exercises was not significantly different [Hemanssen, 1970 #3]. In contrast, Miyamura and Honda (1972) observed no significant difference in SV, and significantly higher HR in TM testing, however their results supported the higher VO_{2 max} values for TM running. Miyamura and Honda (1972) also noted a higher a-vO₂D in maximal TM exercise, which they said indicated a difference in muscle mass utilised in each exercise, with likely increased amounts of muscle used in running.

Runners

A study on 9 highly trained long distance runners and 9 "reasonably" trained controls tested the VO_{2 max} on the TM and CE. Their results showed the TM vs CE VO_{2 max} difference to be influenced by the training state of the subject. The trained runners had on average a 12.8% higher VO_{2 max} on the TM compared to the CE than the control group, the control group showing no significant difference in VO_{2 max} between the TM and CE. This indicates that TM and CE values are influenced by the training conditions of the subjects. When testing highly trained runners, it is essential that VO_{2 max} testing be carried out on the TM for accurate results since it appears the difference between TM and CE values are even more marked in highly trained subjects compared to their less trained controls. These findings support the specificity of training theory, since the difference in physical work capacity between runners and controls is underestimated by a non-specific test, eg CE.

A later study lends further support to the specificity of training view on VO_{2 max}. Their study on 10 endurance cyclists and 10 endurance runners found correspondingly high values for VO_{2 max} when measured during the specific trained activity, runners producing significantly higher values on the TM test (68.1ml/kg/min) compared with the CE test (61.7 ml/kg/min). These testing specificity results were supported by Stromme (1977), who tested 37 athletes made up of cross-country skiers, rowers and cyclists. All were tested on an uphill TM run, and during maximal performance of their chosen sport. All groups obtained higher VO_{2 max} values in their chosen sport. Stromme expands on the theory of specificity by stating that the increases in VO_{2 max} seen more noticeably in sport specific training, are due to facilitation of oxygen transport and by adaptive changes in the metabolic characteristics of the active muscle fibres.

Cyclists

In 1978, Hagberg et al tested a group of trained competitive cyclists to assertain whether they could attain as high a VO_{2 max} on the CE as on the treadmill. In contrast to other studies, these authors found that VO_{2 max} values were similar for TM running, CE and cycling on the TM. In fact, they found that the VO_{2 max} was slightly higher on the CE test, however these values did not reach statistical significance, possibly due to the low subject numbers (n=6). Coyle et al (1988) studied 14 cyclists who had been training intensively for 3-12 years to determine factors associated with endurance performance. In preliminary testing, they also found these trained cyclists to have a similar VO_{2 max} on both TM and CE tests.

These authors agree with others who suggest that the lower VO_{2 max} seen in untrained subjects during CE testing is due to local quadriceps muscle fatigue during maximal effort cycling. This local muscular fatigue limits the work performed before the central circulatory system is maximally engaged. It has been stated that during cycling, the peak load during a revolution is twice the actual load setting on the cycle . Low pedal frequencies during maximal effort therefore result in great tension development in each contraction, developing local fatigue and limit performance before maximal demand is placed on the oxygen transport system, yielding a low VO_{2 max} value.

Triathlon

Studies on triathletes have again supported the specificity of training response. The general finding was that the VO_{2 max} and LT of triathletes when tested on the TM and CE were higher than in the general untrained population, but not as high as athletes training in one sport alone. This was attributed to the amount of training time, which was directed at all three disciplines and consequently was less in any given individual sport compared with single sport athletes. These studies also supported the finding of a higher VO_{2 max} in TM testing compared with CE and swim testing.

Sub-maximal exercise

Another study supports the specificity of training view, not only with respect to the VO_{2 max}, but also when measuring the AT as a % VO_{2 max}. Their study on 10 endurance cyclists and 10 endurance runners found that the AT was reached at a higher % VO_{2 max} in the subjects' specific activity (TM or CE), compared with the untrained subjects' values. They alsoagree with Coyle (1988) that it is local rather than central adaptations that are responsible for the reduced lactate levels during submaximal exercise, indicating the adaptations in local exercising muscles as listed under "peripheral mechanisms" above. This has the effect of increasing the AT and glycogen sparing for endurance exercise . They found the AT to occur at a generally higher % VO_{2 max} on the TM, followed by the CE and then the arm ergometer. They attribute this to the arm ergometer using a small muscle mass, and the subjects unfamiliarity with the task.

Hermansen et al (1969) and Hermansen et al (1970) observed a difference between CE and uphill TM during submaximal work in blood lactate levels, pulmonary ventilation and HR which were all higher in CE vs TM [Hermansen, 1969 #9; Hemanssen, 1970 #3].From these study they concluded that the haemodynamic response is different in cycling and running, and that the CE and TM should not be used interchangeably during longitudinal studies. Care must be taken in generalising these results however, since the subjects varied in their physical fitness levels, training levels and cycle experience which has been shown to affect physiological cycling performance.

Coyle et al (1988) studied 14 cyclists who had been training intensively for 3-12 years and who had similar VO_{2 max}, (as measured on TM and CE) and divided them into 2 groups according to whether they reached their LT at low or high intensity exercise. The values were very similar for TM and CE testing. They measured endurance performance (timed sustaining 88% VO_{2 max}), glycogen utilisation,and lactate responses. Their results indicated that VO_{2 max} is an important determinant of endurance performance. Also, that endurance during sub-maximal exercise is closely related to factors that control muscle glycogenesis and blood lactate concentration. They concluded that the best predictor of performance time to fatigue was the %VO_{2 max} at LT, the two variables most related to this value being the number of years of cycling, and the percentage of Type 1 muscle fibres. The difference in performance ability during high intensity submaximal cycling is highly related to a combination of lactate production (glycogen utilisation) and lactate removal (capillary density). It is noted that in these subjects, more than 2-3 years of intense cycle training promotes continued neurological and/or muscle adaptation that reduces muscle glycogenolysis specifically when cycling. They highlighted the fact that individuals with similar VO_{2 max} values can vary greatly in glycogen utilisation and time to fatigue when cycling at the same work rate and %VO_{2 max}.

Clinical Implications

The implications for aerobic training are twofold, relating both to training and testing. If the main goal for a particular patient is simply to maintain aerobic fitness, then running provides a good exercise, since it uses large muscle groups, resulting in a more general cardiovascular adaptation which is transferred to other types of training. Cycling produces a limit on the central system due to fatigue in the peripheral system in untrained individuals prior to overload of the central system. Other methods of cross-training also appear to maintain aerobic capacity for a short time as long as the frequency, intensity, duration and rest periods are similar to that of the trained sport. This has significant implications for the injured athlete who wishes to maintain cardiovascular fitness while they are unable to train in their sport.

If the goal for the athlete is to improve endurance performance, then it is essential that training overload both the central and peripheral system in the manner required by the sport in order to achieve physiologic adaptations specific to the sport. In other words, runners must run and cyclists must cycle.

When testing athletes, either for baseline measures, or to evaluate the effects of a training programme, the test must simulate as closely as possible, ideally be identical, to the method of training. From the studies reviewed, it would appear that the more highly trained the athlete is in their sport, the more important it is to match exactly the training and testing conditions in order to get an accurate value. Testing in a non-specific manner may significantly underestimate the aerobic adaptation resulting from training.

Inherent testing difficulties also highlight the need for highly standardised and validated testing and measuring procedures. Given these difficulties, it is also important to make the athlete aware of the margin of error of any given test to avoid potential psychological sequelae such as disappointment, frustration and confidence in the training personnel when results may not reflect the effort of training.

In untrained individuals, the TM and CE test remain the most practical to perform, however due to the lower CO and smaller muscle mass employed on the CE, the VO_{2 max} values may be underestimated. When testing untrained individuals, one must also consider the physiologic parameters to be tested. It is possible that maximal exercise testing in an untrained individual may result in injury or muscle soreness. For these reasons sub-maximal tests should be considered, and the extrapolation of these results to maximal aerobic capacity values carefully interpreted due to the known inherent error in this procedure.

Conclusion

The factors used to measure aerobic capacity are theVO_{2 max}, the %VO_{2 max} at LT. LT is considered to be a more accurate predictor of performance than VO_{2 max}. LT is limited by the training state of the peripheral mechanisms, or local musculature. It has been clearly demonstrated that these variables not only show marked differences when measured by means of the trained vs untrained sport. In runners and in untrained individuals, VO_{2 max} is higher when tested on the TM compared to the CE. Only in trained cyclists were these parameters slightly higher when tested on the CE compared to the TM. This indicates a specific training effect of the local musculature in trained cyclists compared to runners and untrained individuals, as well as athletes from other sports. Another method of measuring endurance is the %VO₂ that can be maintained over a period of time (economy of motion), and this has also shown sports specificity. It is clear that these tests need to be carefully carried out and interpreted in order to gain reliable results. Peripheral metabolic capabilities in the local muscles involved in each sport appear to be the limiting factor when in comes to testing the aerobic capacity. These effects are only shown most accurately when tested specifically on the mode of training. A non-specific test will underestimate aerobic capacity due to peripheral limitations before maximal central system stress.

It would appear, from the literature reviewed, that in order to accurately reflect endurance performance in the laboratory, the test must be ideally identical, and at least as close as possible to the sport in which the athlete is trained. In the general population, TM and CE testing remain the most practical, and it still appears that in the untrained population, higher VO_{2 max} values are attainable on the TM compared to the CE, due to the larger muscle mass employed and the higher CO achieved.

In conclusion, from the literature reviewed, it appears that running endurance performance cannot be predicted from cycling performance.

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Short Answer Review Questions

1. Describe the systems involved in adaptation to aerobic exercise.
2. List the adaptations that occur in each system.
3. How is endurance performance measured and what is the major limiting factor
4. for these measures?
5. What are the most common modes of testing endurance performance, and what
6. are the advantages and disadvantages of these?
7. Why does running training have aerobic fitness transfer effects to other
8. forms of exercise?
9. Why do untrained individuals show higher VO_{2 max} on the
10. treadmill compared to the cycle.
11. What is the physiological adaptation occurring enabling trained cyclists to
12. show higher VO_{2 max} values on the cycle compared to untrained
13. individuals.
14. Which physiological parameter is the more accurate predictor of endurance
15. and why?
16. Why do triathletes not show as high VO_{2 max} values as the single
17. sport athletes on TM and CE tests?

Exercise Physiology Educational Resources 2000