Effect of resistance training on the completeness of muscle activation

We examined the completeness of quadriceps activation in resistance trained and untrained men performing maximal voluntary isometric contractions (MVICs). Thirty-eight subjects, aged between 18 and 45 years took part in the study. Eighteen had resistance trained for at least one year whilst 20 had no prior resistance training. All subjects performed at least three unilateral MVIC’s from a seated position with the dominant leg at the knee angle of 1200. Movement of the trunk and pelvis was minimised by the use of a tight five-point harness. MVICs were separated by two minutes of rest. Muscle activation (MA) was determined by applying twin stimuli to the muscle during MVIC’s and five seconds afterwards when the muscle was relaxed. MA was determined from the formula; MA (%) = (1 – SR / RR) * 100, where SR = superimposed response (the force increment noted during the MVC at the time of stimulation) and RR is the response evoked in relaxed muscle. Electrical stimulation (ES) was delivered via two oval shaped self-adhesive electrodes (12*7 cm) placed proximally and distally over the quadriceps. Individual pulses, delivered via a constant-current stimulator (Digitimer, DS7AH), were 50 ms long and separated by 9.5 ms intervals. Despite being significantly stronger, resistance trained men achieved no greater muscle activation than their untrained counterparts (trained = 88.9 + 4.8%, untrained = 89.8 + 5.2%, p = 0.6). Our results suggest that whilst there appears to be scope for improving MA of the knee extensors during MVICs, assessing MA during such contractions is of limited value when assessing the possible neural adaptations arising from resistance training. Improvements in muscle activation after resistance training may be highly specific to the training tasks or non-existent.