While there may be some exceptions to this rule (i.e. sports such as skateboarding, skiing, and snowboarding, where athletes may land on unstable surfaces), true functional balance training for athletes would rely on interventions on stable surfaces to best simulate the demands of the athletic endeavor. Muscle Recruitment Patterns and UST The question of functional carryover also extends to the concern for altered muscular recruitment patterns and reduced force output under unstable conditions. Behm and colleagues (2002) compared knee extensor and plantarflexor activity under stable (seated in a chair) and unstable (seated on a stability ball) conditions.
34 The investigators found that force production under stable conditions was significantly greater than under unstable conditions for both the knee extensor and plantarflexor tests. Stable knee extensor and plantarflexor forces were 70.5% and 20.2% greater than under unstable conditions. Mean quadriceps activation under unstable conditions was 44.3% less than with stable conditions, whereas the plantarflexor deficit was only 2.9% (not statistically significant). EMG analyses of the antagonist muscles revealed that hamstring and tibialis anterior activity increased by 29.1% and 30.3% under unstable conditions as compared to stable conditions (7). More concisely, there was less force and activation of the prime movers and increased activation of the antagonists. The researchers noted that the change in muscular recruitment patterns was likely due to "excess stress associated with the increased postural demands" and "the dispersion of concentration (neural drive) in attempting to control 2 limbs with differing responsibilities (balance and force)" (7). While increased antagonist co-contraction may assist in maintaining joint stability and coordinating movement, it is generally perceived as counterproductive, especially in strength tasks. You shouldn’t be doing leg extensions, but if for some reason you must, your hamstrings shouldn’t be going crazy.
35 Torque developed by the antagonists decreases net torque in the desired direction of movement, and – through the process of reciprocal inhibition - may also impair an individual’s ability to completely activate the agonists (62). Therefore, it can be argued that unstable surface training creates a hesitant athlete for whom stability is gained at the expense of mobility and force production. Sale (2003) noted that two muscular activation alteration patterns have emerged in longitudinal resistance training studies. In some studies, there has been “a decrease in absolute antagonist activation in conjunction with either an increase or no change in agonist activation” (62). In other studies, there was no change in “absolute antagonist activation but increased agonist activation, decreasing the antagonist/agonist ratio” (62). The acute muscular activation patterns observed with unstable surface training work contrary to both of these outcomes, which were observed in
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- Fall '19