Q: What do you think using weight vests for plyometric exercises[. . .]“

A: First of all, you need to establish why you are doing plyometrics and if they are going to benefit you. Many people haphazardly throw plyometrics into their programming hoping it will get them explosive, or often times because they want some kind of metabolic effect from the plyometrics (usually by people “under”fit using high volume plyos). With plyometric sessions, we’re looking at about 15-25 foot total foot contacts per day, 3-4 days per week.

So on to the benefits of plyometrics (don’t worry, I’ll address the weight vest in a second)…We are trying to develop a increase in specific neuromuscular qualities; namely, starting strength, acceleration strength, and explosive strength and on the mechanical end, improve the storage and restitution of elastic energy. With respect to motor units we need to ask “how fast” and “how many”. How fast can we recruit the motor units, and how many can we recruit them? With plyometrics there is limited time to develop force because you are going to leave the ground or an objects, such as a med ball, may be leaving your hands.

In order to develop as much power as possible there are few things on consider. Putting the most force into the ground during the time you have contact will allow you to generate more force, but increasing the time inherently decreases power. This would seem like a plus for the weight vest because it allows you to increase the time on the ground–more weight needs more total force to leave the ground. This could be beneficial at low loads but as the load increases the dependency on force develop shifts more toward a dependence on maximal strength, not explosive strength–essentially nullifying the intended effect of the exercise.

Moreover, when landing the increased load will have an additional accelerative effect (increased kinetic energy due to increased mass). This increase acceleration necessitates a need for greater deceleration, or eccentric muscle activity. The transition from eccentric to concentric is a brief isometric period of elastic energy storage known as the amortization phase. With the increased load, this time interval of this transition increases which allows the stored energy to dissipate as heat. This, in effect, limits the reactive ability.

Can small loads be useful? Certainly to some extent, but remember increased eccentric action will also lead to increased soreness so use caution with volume (or limit other areas of programming). For those not properly conditioned to attenuate accelerated landing this can lead to serious joint pain. My general recommendation is to find other ways to increase intensity and work through a steady progression of plyometrics before considering a weight vest.

–
Ryan