Power and performance

Power and a person’s capacity to perform sport

i’ve copied this article below and have added my comments in italics and highlighted key parts in bold.

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 (how the body works) 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.

 The golf swing and bench press are both power movements, but the golf swing uses hight speed and low force, where as the bench press uses high force and low speed.

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 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.

Because power is closely related to strength the many factors influencing maximal strength will also relate to the development of maximal power performance.  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.

 My example- a sprinter who needs power over 100m but who can’t provide enough energy over that period might tie up at 60m

 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 (best 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 , like goal kicking. which is completely different to the marathon runner who relies mainly on muscular endurance and aerobic capacity.

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 (this is important for goal kicking) 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.

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.

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.Power Indicating Performance (literature)

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.

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.