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Curtin University of Technology
School of Physiotherapy

Power is the most important factor in assessing a person's capacity for performance in sport!

Topic for Summary and Critique - by Chris Perkin

Contents

Statement of the Topic

Power is the most important factor in assessing a person's capacity for performance in sport!

Introduction

To properly discuss the topic of power predicting performance many areas of the question first need defining. The definition of power will be discussed in relation to muscular power as well anaerobic and aerobic power measures which are regularly utilised as performance indicators. One must then consider the multiple factors including power that can influence the capacity of performance in sport. Specific consideration will be given to the physiological factors, discussing the energy systems and also the measurement of strength and power.

A close look into specific sports and athletic pursuits is also required to more relevantly relate the measurement of properties such as power to the individual sports. To date there continues to be debate on the optimum measures of human performance. Power certainly does have a role to play is most sporting activities but to what extent hopefully this review will shed some light.

Power

In terms of pure physics power is well recognised as rate at which work can be done. It is the work done per unit of time. In physical terms, work is done when an object is moved against the resistance of an opposing force: Work = force x distance. So using the above two formula power can now be seen as : power = force x distance / time. Since speed is distance over time, power is also equal to force x speed. In athletic situations it is closely related to the development of strength and speed. Rushall and Pyke (1990) define it as a function of both the force ( strength ) and speed of movement.

From this information one could assert that any movement is a power movement, for all movements entail some strength and speed. However a very fast movement such as the golf swing seems to require small effort and is often referred to as a speed movement. In contrast when an activity such as a maximal bench press is performed requiring heavy effort then it is seen as a power movement. The two concepts are interrelated and the performance of power or speed activities is dependent on their interrelationship. Every activity which may be very individual has a desirable speed of performance that is combined with a maximal level of useable strength (Ellis et al 1998, Rushall and Pyke 1990). This is important when considering power in regards to performance. Like strength measurements not all power is considered maximal and within sport it must be noted that maximal power achievement is not always required However the use of power does exist and confusion arises regarding the type of power measurement to attain.

Abernethy et al (1995) additionally suggests that strength and power can be considered the forces or torques generated during sporting activity. Because strength is a component of power it must also be considered an important factor when measuring performance. Brukner and Kahn (1997) note power as the equivalent of explosive strength. This relates to the so called power events such as jumps, sprints and throwing events where the athletes body is propelled - by jumping or sprinting or an external object is projected such as a shot or javelin (Watson 1986). But to describe it is explosive power may be poor terminology as it is simply another measure of power measured in watts.

It is believed that the specific power movement or activity are purely learned actions. Their improvement may be primarily determined by a neural reorganisation of existing physical structures and attributes. Grabe and Widule (1988) described motor learning of the skill associated with the activity as the major determinant in establishing the explosive power training effect. This specific motor learning pattern is important to consider when aiming to test power for performance in the clinical setting.

Because power is closely related to strength the many factors influencing maximal strength will also relate to the development of maximal power performance. The muscle structure and function and fiber type are all factors that contribute to strength and thus power production (McArdle et al 1997). The rapid ability of the muscle to shorten and produce contraction is seen as an indiaction of power. The power qualities of some athletes depend on the ability of the muscle to contract with speed and force. This is linked to the muscle fiber type being either fast or slow twitch. Fast twitch motor units are more closely related to power and are of vital importance to explosive activities or short intense efforts. Slow twitch motor units are more advantageous to endurance athletes and the adaptability of these fibres in generating force and power is not high.

The definition of power so far relates to muscle force production over a specific time period but power also relates to the rate at which energy may be provided and utilised. This often relates to the energy systems and to measures of anaerobic and aerobic power which are other factors influencing the capacity of performance. This will be discussed under the review of energy systems but firstly we must recognise the many other factors that contribute to sports or athletic performance.

Factors Affecting Performance

One problem regarding the single use of power to indicate performance capacity is the multiple factors which will combine to produce optimal performance. Sporting performance can be seen related to three general factors being skilled technique, physiological fitness and psychological skills (Rushall and Pyke 1990). At an elite level it is important that each component provides to the overall performance capacity. There are however differences to the degree in which optimal performance relies on any one of them. Practical examples may include the golfer who requires a very specific learned and skilled task with high technical skills which is completely different to the marathon runner who relies mainly on muscular endurance and aerobic capacity.

The components of performance can further be classified to discuss the main physiological aspects. The first may relate to the cardiorespiratory endurance often referred to as aerobic power. It relates to the ability to transport oxygen to the muscles by the respiratory and cardiovascular systems and will be discussed soon.

As already indicated the muscular endurance relates to the ability of muscle groups to sustain activity and this can also be a limiting factor for performance. The continual performance of muscular activity also relates to the anaerobic energy systems supplying energy and the build up of lactic acid which occurs with prolonged activity.

Muscular power has already been defined and as indicated relates to the product of muscular strength and power. Different tasks require varying combinations of strength and speed such as the comparison of weight lifting versus baseball pitching.

General muscular and joint flexibility must also be considered as an indicator of performance. It relates more commonly to sports that require a great amount of movement such as swimming, diving and gymnastics.

Other influences requiring consideration include genetic endowment, age, gender and training. All sports involve different physiological requirements so when discussing assessment of performance it is imperative to know and understand the most appropriate components relevant to the sport being tested. The specific assessment of performance will be discussed soon.

Energy Systems

The energy requirements for sport and athletic activities varies considerably depending on the type of task being performed. The energy systems can be classified into the anaerobic and aerobic system and most activities generally require the use of a combination of systems for energy fulfillment. The anaerobic system is classified further into the immediate supply via the "alactic" or adenosine triphosphate-creatine phosphate (ATP-CP) and the short term energy supply from the "lactic" or gylcolytic pathways of energy supply. For more sustained and longer term energy supply the aerobic system is utilised by the process of oxidation.

Each energy system can provide supply specific to the requirements of the activity. For the specific time frames one should refer to the energy-contribution / performance time relationship as outlined by McArdle et al (1997). The ATP-CP system provides for the first 5-10 seconds and relates to speed and strength activities thus being very important to the production of power within performance. The recovery of this system is relatively quick with only periods of 30 seconds required to be replenished and then apply repeat effort. If high energy tasks are required greater than 10 seconds then the breakdown of glycogen to glucose and lactic acid occurs via glycolysis. This can maintain muscular contractions between 30 -40 seconds. This is used commonly in sustained sprint or muscular endurance activities as seen in most team sports. The presence of large amounts of lactic acid can interfere with muscle shortening and prevent activity if accumulation is allowed. The recovery of the lactic system is longer.

The oxidative or aerobic energy system generally assists with energy supply after 2-3 minutes. This initially is used for assistance to continue energy requirements while the short term and immediate energy supplies are replenishing. After three minutes of lower intensity prolonged exercise the aerobic system takes over as the prime energy source. Usually there is a mixture of glycogen and fat used as a fuel in prolonged efforts (McArdle et al 1997, Rushall and Pyke 1990).

Energy Systems and Performance

Athletic performance can be classified into energy systems and related to power output. Generally sports or tasks can be considered a low power task or a high power task. The lower power activities may include endurance based athletes such as a long distance swimmer or runner. They rely more on the aerobic energy system and generally muscular power in not a good predictor of performance due to muscular strength and bursts of speed not being a major determinant of the sport. In contrast the measure of aerobic power which is a frequently utilised testing measure seen as VO2max can help predict marathon performance as indicated by Hagan et al (1981). Despite VO2max not being a true indication of power as described by work / time or strength x speed it is a term that must be considered when discussing performance. It can be potentially converted to a measure in kcal/kg/second and then described more relevantly as power.

The high power tasks can be classified as using the anaerobic energy systems. They are split into the alactic and lactic systems. The short explosive type efforts are seen in sports such as weight lifting, jumping tasks, sprint activities. Normally the sports requiring very intense single efforts or short bursts of intense activity require sufficient use of the ATP - CP or alactic system. The glycolytic or lactic system is used commonly by sustained sprint activity such as the 100 - 400 metre run events, sprint cycling events and also many team sports needing short repeated efforts of intense activity.

Evaluation of Energy Systems

Performance tests that cause maximal activation of the ATP-CP energy system have been developed to evaluate the capacity of these systems in producing performance. These tests are generally referred to as power tests. It does relate to the early definition of the time rate of doing work. It is often referred to in watts.

A stair sprinting power test is described by McArdle et al (1997). The power is the product of the persons mass and vertical distance covered divided by time. Using this measure indicates that a heavier person would have a greater power but this is not supported by evidence so caution is used when using these such results.

Another commonly used power task is the vertical jump test. The counter movement test involving a step before the vertical jump and no arm swing is seen as a test of leg power (Young 1994). In analysis of this power test it fails to adequately measure a persons ATP-CP energy transfer capacity but it does provide a sports specific explosive test for sports such as basketball, volleyball and netball. It would help predict performance relating to a specific component of these sports rather than the overall capacity of the sport.

Other tests involving all out exercise of 6-8 seconds is sometimes referred to as a measure of anaerobic power as it measures the ability to supply energy over a short period of time. Finn et al (1998) indicates that peak power has been expressed as the highest power output averaged over periods between 1 and 5 seconds. A 10 second all out exercise test on a bicycle ergometer is described by Telford et al (1989) and a repeated effort cycle ergometer test of 5x 6-seconds as discussed by Ellis et al (1998) are commonly referred to as anaerobic power assessments. Telford et al (1989) concede the general capability of these tests however still indicate that there may be potential for talent identification using this test profile. For performance indication in elite athletes testing procedures must be very specific but general tests do provide some insight. Green and Dawson (1993) add that anaerobic capacity is an important factor mainly in those events where it is nearly completely maximised such as the 800-metre run or 1000 metre cycle pursuits.

The most widely used of all the ergometric tests for anaerobic power has been the 30 second Wingate test (Inbar et al 1996). In this test power output was obtained from pedal frequency and resistance. Peak power was averaged over 5 seconds and mean power over the 30 seconds. Rate of fatigue can also be computed as the rate of decline in power relative to the peak value. The assumption is that the value for peak power represents the energy capacity of the high-energy phosphates, while the average power represents glycolytic capacity (McArdle et al 1997). The performance scores are reproducible and validity of this test is considered moderate . One aspect that isn"t considered is the aerobic contribution to the 30 second test which creates some controversy especially when using the test as a anaerobic power and capacity indication.

Another more worthy addition to the discussion of power is the concept of critical power. It involves a hyperbolic relationship between power output and the time that power output can be sustained. It is defined as the maximum rate of work that could be sustained for a very long time without fatigue. It is seen related to fatigue threshold, the ventilatory and lactate thresholds and maximum oxygen uptakes (VO2max) and it is seen as a measure of aerobic fitness. The concept of critical power is further discussed by Hill (1993).

As previously indicated the long term energy system is frequently tested using various procedures to attain VO2max. One such test is the multistage fitness test described by Ellis et al (1998). This has found to be a reliable estimate of aerobic power (Brewer et al 1988) and it is a somewhat sport specific and also easily administered protocol. The measurement of aerobic power does provide an accurate measurement of the long term energy supply and provides positive correlation with performance in endurance based activities (Hagan et al 1981, Hawley and Noakes 1992, Marsh and Martin 1997).

Power Indicating Performance (literature)

Some sports are more commonly associated with predictive tests for performance. Generally these involve activities which are at either ends of the energy system continuum. The sports involving short, single efforts of activity or those involving the long term endurance contributions.

Cycling has much research devoted to it's levels of performance. Bentley et al (1998) noted significant correlation between cycle time and absolute Vo2 max and wmax which is a peak power output. They concluded that in their study on triatheletes peak power output is a useful variable in assessing cycle performance. Smith et al (1999) who similarly studied the performance of cycling reported critical power tests cited being highly related to 17km and 40 km time trial performances. Hopkins and McKenzie (1994) also studied endurance cyclists and their results revealed that power output at the ventilatory threshold (VT watts) was correlated with race performance time and calculated power output during the competition (r = -0.81; r = 0.82). The data indicated that simple laboratory measures can predict time trial performance in trained cyclists.

In a study by Houmard et al (1991) on middle distance runners the battery of tests used indicated the aerobic power does have some effect on performance but also that the vertical jump and power run tests used as apart of the anaerobic systems influence middle distance performance in runners of similar abilities.

When discussing the use of power to measure potential performance in sport the general testing procedures utilised don"t always appear relevant to the activity being tested. Horswill (1992) opposed these suggestions and indicates that the margaria stair climb test and the wingate anaerobic tests do have positive correlation with the successfulness of the wrestler. The energy requirements of wrestling and other intermittent sports is quite complex and demand both aerobic and anaerobic energy systems that are well developed. Often prediction of capacity for performance may require testing protocols that relate specifically to the activity and energy requirements within the sport. Power is certainly one measure used regularly in the testing of these energy systems but now we must also discuss the power relating more to muscular strength and speed.

Muscular Power

The main difficulties with describing muscle power is discussed in detail by Abernethy et al (1995). These include the fledging status of research in the area, limited understanding of the underlying mechanisms of power performance and also the limitations with various dynamometery in strength and power assessment.

Muscular strength and power are sports specific indices. The athletes power during competition is applied in varied postures, with specific movements at particular speeds. This raises the issue of validity of many current testing procedures especially much of the dynamometry utilised. Because it is difficult to often mimic sporting movements the assessment of muscular power is often non specific. Despite this, testing protocols for strength and power as well as training programs are continually performed so we must continue to review and aim to formulate procedures or programs over time relating specifically to performance. The strength training literature currently notes various forms of training for strength and power. Controversy still exists regarding the amount of repetitions to perform to get a true measure of power. To date 1 repetition maximum (RM), 5RM, 10RM and more have all been utilised however there is no specific guidelines set for this form of assessment (McArdle et al 1997). The other issue is consideration of concentric and eccentric muscle actions which will not be further discussed in this review. To continue with the discussion regarding strength and power assessment a review of dynamometry is required.

Dynamometry

This measures the power associated with tasks where the load or velocity of movement is held constant. The three modes of exercise are described as isometric, isotonic and isokinetic. It is important to understand when discussing assessment of power it yields different results to the measures of strength and will provide different interpretations regarding the effects of training (Abernethy et al 1995).

Isometric testing is difficult to justify a true power activity because by definition power = work / time and because work is force throughout movement then there is no power output as there is no movement produced. Abernethy et al (1995) does suggest that the rate of force development during first period (60-100msec) of the isometric contraction is used as a measure of athletic power. The rationale indicated for the use of this measure is that the time available to generate force is limited amongst many sports and this is seen in gymnastics, sprinting and jumping activities. A criticism however is that the measurements aren't dynamic thus not valid for performance indicators.

Isoinertional measures of strength are commonly used to mimic many different weight lifting tasks. But the measure of power may be more specific to performance as the strength activity needs to be performed over a short time. Even though debate still exists regarding the specific nature of the task it still appears that isoinertial testing allows a useful prediction of performance over many sporting activities (Abernethy et al 1995).

Finally isokinetic assessment has a further advantage that there is high measurement reliability and objectivity (Dvir 1995). Average or peak power measures and velocity-power curves can be produced but criticism still exists regarding the relationships to sporting tasks. Despite this, correlation does exist between isokinetic testing and performance in sprint and vertical jump tests (Perrine and Edgerton 1975).

Despite the large amounts of research using dynamometry there is still relatively limited information relating power measurements to athletic performance. More research is shown relating strength measures to sporting achievements. Dynamometry still remains useful in monitoring training effects and in strength and power diagnosis of specific muscle groups but no one protocol exists to provide all information regarding athletic pursuits. It can be used as a component of the multiple factors contributing to overall sporting perfromance.

Conclusion

In reviewing the topic of power in respect to predicting performance many factors need to be considered. The integration of energy systems, muscular strength and sports specificity are the main factors creating a difficult form of assessment. Power is a term that is used regularly and incorrectly at times in the assessment of performance and because all sporting tasks require a form of power as an assessment tool it appears very appropriate. Specificity is another term that must be realised. To achieve the most appropriate measure of ones performance and capacity for performance then all testing procedures used should relate to the requirements of the task.

Performance is a complex mix of physiological, psychological and technical abilities so assessment should also address all these issues and in light of the debate power should always form part of the assessment of performance.

References

Abernethy P, Wilson G and Logan P (1995)
Strength and power assessment: issues, controversies and challenges. Sports Medicine 19:401-417.
Brukner, P.& Khan, K. (1993)
Clinical sports medicine. Sydney: McGraw-Hill
Dvir Z (1995)
Isokinetics: muscle testing, interpretation and clinical applications. New York: Churchill Livingstone.
Ellis L, Gastin P, Lawrence S, Savage B and Sheales A (1998) Testing protocols for the physiological assessment of team sport players. In Gore J (Ed) Test Methods Manual (3rd Ed). Canberra: Australian Sports Commission.
Grabe SA and Widule CJ (1988)
Comparative biomechanics of the jerk in Olympic weight lifting. Research Quarterly for Exercise and Sport 59:1-8.
Green S and Dawson B (1993)
Measurement of anaerobic capacities in humans: definitions, limitations and unsolved problems. Sports Medicine 15: 312-327.
Hagan RD, Smith MG and Gettman LR (1981)
Marathon performance in relation to maximal aerobic power and training indices. Med Sci Sports Exerc 13:185-9.
Hawley JA and Noakes TD (1992)
Peak power output predicts maximal oxygen uptake and performance time in trained cyclists. Eur J Appl Physiol 65:79-83.
Hill DW (1993)
The critical power concept. A review. Sports Medicine 16:237-54.
Horswill CA (1992)
Applied physiology of amateur wrestling. Sports Medicine 14:114-143.
Hopkins SR and McKenzie DC (1994)
The laboratory assessment of endurance performance in cyclists. Can J Appl Physiol 19:266-74.
Houmard JA, Costill DL, Mitchell JB, Park SH and Chenier TC (1991)
The role of anaerobic ability in middle distance running performance. Eur J Appl Physiol 62:40-3.
Marsh AP and Martin PE (1997)
Effect of cycling experience, aerobic power, and power output on preferred and most economical cycling cadences. Med Sci Sports Exer

Short Answer Review Questions

  1. Fully define the term power.
  2. List and describe the factors affecting sports performance.
  3. Describe the limitations of the energy systems and relate it to sporting examples.
  4. Indicate different tests used to assess aerobic and anaerobic power.
  5. Discuss the advantages and disadvantages of dynamometry for measurement of power.
  6. Provide examples of power assessment indicating performance within sport.
  7. Discuss the term specificity in relation to power assessment
  8. Outline areas for improvement for the use of power in predicting performance in sport.

Exercise Physiology Educational Resources 1999