Power, in physics, is the "rate at which work is performed," i.e. work is the "product of force and distance" (Work = Force x Distance). [1]
In mechanics, the work done on an object is related to the forces acting on it by
where
- F is force
- Δs is the displacement of the object.
What this usually translates to is the ability to exert maximum muscular contraction instantly in an explosive burst of movement, ie. the ability of a muscular unit, or combination of muscular units, to apply maximum force in minimum time.[2] The two components of power are strength and speed, as with power exercises. (e.g. jumping or a sprint start, snatch, clean and jerk, etc.) [3] Power is a vital component of motor fitness, and is applicable especially to a myriad of athletic activities, and therefore it should not be neglected. Despite the importance of power for athletics and function, the ability to produce powerful muscle contractions decreases with age, more so than other components, such as cardiorespiratory endurance. This decline also appears despite persistent training and otherwise good health.[4]
For a program which includes power training to achieve maximum effectiveness, a strong initial focus should be on maximizing strength. For example, to experience the greatest improvement in speed and explosiveness when undertaking an explosive-type training program which includes plyometrics, athletes should first have a strong strength base. Undertaking a plyometric program without first developing greater levels of strength may make an athlete more explosive and quicker but not to the extent if the program had first focuses on increased levels of strength.[5] One must also take into consideration, however, the force-velocity curve when considering a optimum balance between strength, speed, and power. Most athletic movements do not involve slow contractions at near maximum force, but are characterised by mid-to-high velocity.
[edit] Measuring Power
As mentioned, power is a product of force times distance over time. To quantify power output, numbers need to be consistent in the form of SI units, and the result is measured in watts. SI units are as follows:
Distance in Meters
Mass in Kilograms
Force in Newtons
(A newton is the force required to accelerate 1kg 1 meter per second per second. For practical purposes, this equals 9.8kg)
Time in Seconds
Work in Joules (newton * meters)
Power in Watts (joules/seconds)
Example: Determine the power output of an athlete who lifts a 50kg weight, a height of one meter, for eight reps, in 40 seconds:
Newtons = (50kg*9.8m/s) = 490n
Joules = (490*1m)= 490nm
Watts = 490nm/40s = 122.5 * 8reps = 980w
(When measuring watts through a rotatary activity, work is expressed as torque (in newton meters) times the angular displacement in radians (1rad = 180/π). The distance unit is the length of the moment arm.)
Using the formulation for wattage, different activities can be compared one to the other in similar terms.
[edit] Enhancing Power
Many methods have been employed in attempts of enhancing power; some methods include incorporation of explosive lifts, such as Olympic Lifts, into routines to incorporation of plyometrics. Plyometrics exercises are based on the understanding that a concentric (shortening) muscular contraction is much stronger if it immediately follows an eccentric (lengthening) contraction of the same muscle. In addition to this, plyometric drills can closely mimic both the movement pattern and the speed of execution of actual sports performance, as opposed to traditional resistance training.[6]
[edit] Plyometrics
With regards to integrating plyometrics into programs, studies have shown that contrast loading or "complex training", which involves lifting at >85% of 1RM on a strength exercise followed by an explosive exercise or load of around 40% 1RM, is more effective at producing enhanced power output than constant loading (when the weights stay the same).[7] Some authorities recommend that an athlete should be able to half squat at least 1.5 times their body weight before undergoing a plyometric program, but other claim this may be excessive.[6] Plyometric training can also be periodized just like any other type of training.
Resistance training plays a vital role to play in laying the foundations for greater power (power = strength x velocity) and pre-conditioning an athlete for plyometrics. Resistance training can facilitate a larger and stronger muscle, which will be able to generate greater force plyometrically; additionally, strengthened tendons and muscles will be less prone to strains and pulls.[6]
The volume of plyometrics training during a session is inversely proportionate to the intensity of the plyometric exercises (intensity measured in foot contacts); the more dynamic the move and the greater the power generated, the fewer foot contacts are required.[6]
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