Power

Curtin University of Technology

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

Proposition for Debate - by Rahul Madan

Statement of the Topic

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

Power: Definition and Types

Power and physical performance have been closely related and investigated by various investigators using different protocols. The ability of an athlete to produce high forces at high velocity is an important component of the physical performance and functional capacity. There is no agreement in the literature over the definition of power. However, power has been defined as the product of force (or torque) and velocity, ie, rate of doing work (Thomas et al 1997). It is of two types, aerobic or endurance and anaerobic.

According to Brukner and Khan (2001), power is the equivalent of explosive strength. Young and Bilby (1993) have used the term "speed-strength" synonymous with power. Paavolaienen et al (1999) have suggested that muscle power is the ability of neuromuscular system to produce power during maximal exercise when glycolytic and oxidative energy production is high and muscle contractility may be limited.

Schmidtbleicher (1992) has defined power as the ability of neuromuscular system to produce greatest possible impulse in a given time period, which depends on resistance of the load, and organisation of the acceleration. The latter parameter is influenced by the sport played by the athlete. There are others factors as well, which are pertinent for power generation. The exploration of these factors is important for understanding the alterations in the power production under different conditions.

Factors Influencing Power

Maximal velocity of shortening has a significant influence on power output. It is dependent on intrinsic speed of the muscle contraction. The proportion of the muscle fibre type and length of the muscle determine the maximal velocity. Type-I muscle fibres generate less power than type-II. Muscle shorter in length has few sarcomeres in series and hence, generates less power. Maximal velocity can not be changed by training.

Maximal isometric strength is directly proportional to power output. Determination of appropriate external resistance for maximum power can be used to establish adequate training stimulus to train muscle power. There is controversy in the literature as to maximum external resistance against which muscle power can be generated. According to Thomas et al (1997), training to improve maximal power output should be done at 56-78% of the maximum dynamic strength. Although there is no agreement for the various training protocols to achieve this objective but cross sectional area and neural adaptations of muscles in response to training must be addressed.

Muscle strength and power are inseparable variables and have direct confluence on physical performance. According to Sale (1991), muscle strength is the peak force developed during a maximal voluntary contraction under a given set of conditions. These conditions comprise of speed of movement, posture, and patterns and mode of contraction. The role of different modes of muscle contraction like isometric, isotonic and isokinetic, and their relation with power has not been accounted for and is beyond the scope of this debate.

Neuromuscular characteristics as a determinant of power and hence, physical performance was interpellated by Paavolainen et al (1999). They found that force-time characteristics differed with different muscle fibre types. Force output of muscle contraction was reported to depend on the rate and force of myofibrillar cross-bridge cycle activity, and effective storage and release of elastic energy during stretch - shortening cycle.

Anaerobic characteristics have also been reported to impair muscle contraction on the inchoation of fatigue which results in increased H+ ion concentration and increased blood lactate concentration thereby impeding muscles' physiological process (Paavolainen et al 1999).

Power and physical performance

Paavolaienen et al (1999) investigated neuromuscular characteristics and their relation with muscle power and physical performance. The important findings are shown in Table 1.

Table 1. Correlation coefficients for the selected aerobic power and running economy variables and the distance and treadmill running performance. (p <>

	VO2 max demand	RE track	RE tread	VO2 max	RCT
V5k	0.78	-0.69	-0.53	0.56	0.74
VO2 max demand	1	-0.66	-0.57	0.57	0.73

V5k

mean velocity of 5 km trial

VO2 max demand

peak treadmill running performance expressed as maximal O2 demand

VO2 max

treadmill max O2 uptake

RCT

respiratory compensation threshold

Paavolaienen et al (1999) found that peak treadmill running performance was a good predictor of track running performance. There was a significant correlation between V5k and VO2 max demand .Maximal velocity of maximal anaerobic running test was found to be significantly correlated with V5k. Therefore, maximal velocity of maximal anaerobic running test was reported to be a staunch implicit indicator of muscle power.

Chelly et al (2001) have reported a significant correlation between the maximal track running velocity and treadmill velocity (r=0.84, p < r="0.62,">

According to Thomas et al (1996) who studied the relation of leg power with the body composition, strength and function in young women; double leg press showed a significant correlation with vertical jump (R2 = 0.584, p <>

Controversies and Loopholes

There was a lack of a comprehensive, precise and absolute definition of power in the literature. There was no agreement over the methods of assessing power and various physical performances. There was a variable subject population with inhomogeniety evident in their sports, level of involvement in sports, age, body composition and stature. There is also a paucity of evidence in the literature for reliable and valid techniques for power evaluation. Some studies could have used better study design to answer the hypothesis.

The key components like muscle strength were acknowledged but not assessed in some studies. Few outcome variables, which were utilised to assess power, were not accepted as gold standard. Following examples are quoted in favour of above-mentioned controversies and loopholes.

Thomas et al (1997) recruited sedentary untrained female subjects in their study. Hence, the results can not be generalised to elite population. Two different kinds of equipment were utilised to assess muscle power namely, double leg press and leg extensor power rig. Given that the two machines used to evaluate power involved the similar group of muscles, there was no agreement between two outputs. It may be because double leg press measures the power output through the full range of motion and requires the subject to overcome the initial inertia of the flywheel to which it is attached. On the other hand, leg extensor power rig uses pneumatic piston and evaluates the individual�s ability to generate power internally against a relatively low resistance. Muscle strength was not assessed though it has been mentioned to be the key component of power development.

There was an oversimplification of assumptions by Chelly et al (2001) in calculating hopping stiffness by spring mass model. This model did not account for harmonic oscillation during running performance. They also considered leg muscle volume to be an indicator of muscle strength and muscle power, which is in contrast to the findings of Maylia et al (1999).

Maylia et al (1999) conducted a study on 11 subjects and measured thigh muscle bulk, and knee extensor and flexor peak torque using an isokinetic dynamometer. They reported that there was no correlation between muscle power and thigh girth individually or as a group. Chelly et al (2001) failed to address the issue of muscle strength and its relationship with power. They used simple ergometric treadmill to evaluate and assess muscle power rather than accurate equipment like high-speed cameras and long force platforms used by other investigators. It could have biased the power assessment allowing the error factor to influence the final results.

Conclusion

Muscle power & physical performance are inseparable, mutually related entities, which can be used to assess an athlete's physical performance in sports. However, there is a lack of agreement in the literature over the power being the most important factor in assessing a person's capacity for performance in sport.

References

Brukner P and Khan K (2001)

Clinical Sports Medicine. (2nd ed.) McGraw-Hill Book Co. Sydney

Chelly SM and Denis C (2001)

Leg power and hopping stiffness: relationship with sprint running performance. Medicine and Science in Sports and Exercise 33:326-333.

Maylia E, Fairclough JA, Nokes LD and Jones MD(1999)

Can muscle power be estimated from thigh bulk measurements? A preliminary study. Journal of Sports Rehabilitation 8:50-59.

Paavolainen LM, Numella AT and Rusko HK (1999)

Neuromuscular characteristics and muscle power as determinants of 5-km running performance.Medicine and Science in Sports and Exercise 31:124-130.

Sale D (1991)

Testing strength and power. In J MacDougall, H Wegner and H.Green (eds), Physiological Testing of the High Performance Athlete (2nd ed.). (pp21-106). Champaign: Human Kinetics Publishers.

Schmidtbleicher D (1992)

Training for power events. In P. Komi (Ed.) Strength and Power in Sport, Vol 3, IOC Medical Commision Publication.

Thomas M, Fiatarone MA and Fielding RA (1997)

Leg power in young women: relationship to body composition, strength, and function. Medicine and Science in Sports and Exercise 29:1321-1326.

Young WB and Bilby GE (1993)

The effect of voluntary effort to influence speed of contraction on strength, muscular power, and hypertrophy development. Journal of Strength Conditioning 7:172-172.