Strength Development: It's So Simple
By Steven Scott Plisk
When looking for the best way to strength-train athletes go back to your high school physics class and recall:
Power = Force x Velocity
A critical velocity or power output is required to execute any skill. Depending on the movement, power production usually peaks at 30-50% of maximum force or velocity. (Figure 1)
Impulse = Force x Time
In order to executive athletic movements, the object must be rapidly moved through an acceleration path with peak force applied for a very short time (typically about 0.1-0.2 second, whereas absolute max force development requires 0.6-0.8 second. (Figure 2) Brief explosive force production is what separates the good athletes from the not-so-good ones.
Force = Mass x Acceleration
Once the weight is determined, maximal force (relative to one’s strength capabilities) and motoneural activity are only generated if it is maximally accelerated. In fact, since any movement is essentially an act of defying gravity, the central issue becomes - what’s being moved and how fast?
The operative concept in each case is speed-strength. Many believe that speed is independent from strength, when in fact, velocity is the result of explosive force that makes sense if you think about any sport skill in simple mechanical terms.
Swing a bat, throw a football, drive off the ground while running or jumping - all are based on the same principles: the athlete briefly gets into a “power position” and then accelerates into action as explosively as possible. Use the same criterion to gauge the usefulness of any training exercise. This is the reason that movements like olympic-style lifts, plyometrics and medicine ball drills are so effective and the reason they deserve high priority in training.
Two Other Important Points
1. Rate of force production is as important and trainable as amplitude.
A basic goal of most athletic skills is to minimize the time required to execute them, which in turn dictates the amount of force that can be generated. Some believe that rate of force development is only relevant during ballistic movements, but not during basic weight training exercises (where the object is not released).
2. The intent to move explosively can be more important than actual velocity achieved.
Full volitional effort - a deliberate attempt to maximally accelerate the resistance, even if it’s too heavy to move rapidly - yields the greatest neuromuscular excitation and subsequently adaptive response.
Anyway you slice it, submaximal levels of force production and motoneural activation - which are exactly what occurs if the weight isn’t accelerated to the limits of one’s ability, simply don’t make sense as a means of training.
1. Newton R.U., Kraemer W.J. Developing explosive muscular power: implications for a mixed methods training strategy. Strength & Conditioning 16 (5): 20-31, 1994.
Steven Plisk, M.S.,C.S.C.S., is Director of Sports Conditioning at Yale University.