Differences in the log-transformed electromyographic–force relationships of the plantar flexors between high- and moderate-activated subjects

The present study examined the log-transformed electromyographic amplitude (EMG) versus force relationships for the medial gastrocnemius (MG) and soleus (SOL) in high- and moderate-activated subjects. Twenty-five (age = 21 ± 2 year; mass = 62 ± 12 kg) participants performed six submaximal contractions (30–90% maximal voluntary contraction [MVC]) with the interpolated twitch technique (ITT) performed at 90% MVC to calculate percent voluntary activation (% VA). Sixteen participants with > 90% VA at 90% MVC were categorized high-activated group; the remaining nine were the moderate-activated group. Linear regression models were fit to the log-transformed EMG–force relationships. The slope (b value) and the antilog of the Y-intercept (a value) were calculated. The b values from the MG EMG–force relationships were higher (P < 0.05) for the high-activated group (1.27 ± 0.13) than the moderate-activated group (0.88 ± 0.06). The a values and p–p M-wave amplitude values (collapsed across twitches [superimposed and potentiated]) were larger (P < 0.05) for the MG (1.17 ± 0.40 and 8.98 ± 0.46 mV) than the SOL (0.24 ± 0.07 and 4.48 ± 0.20 mV) when collapsed across groups. The b value from the log-transformed EMG–force relationships is an attractive model to determine if a subject has the ability to achieve high activation of their MG without muscle or nerve stimulation.