The influence of air temperature on the EMG/force relationship of the quadriceps.

Surface electromyography (EMG) in the past has been used to estimate the intensity of muscle contraction. These estimates were derived from the EMG/force relationship measured at room temperature. How the surface EMG signal is influenced by varying air temperature as it relates to the EMG/force relationship has yet to be investigated. Thus, this study evaluated the influence of different air temperatures (10, 23 and 40 degrees C) on surface EMG during contractions of the quadriceps muscle. Ten subjects [mean (SD) age 29 (7) years and weight 78.3 (7.8) kg] performed a criterion task of five contractions ranging from 10 to 100% of a maximal voluntary contraction, five times over a 1.5-h period in all conditions. The EMG signals generated from the rectus femoris, and the forces associated with the contractions, were captured on FM tape and subsequently digitized at a sampling rate of 2000 Hz. The relationship between EMG and force was different under the different conditions; EMG was reduced at a given force as temperature increased, and the EMG increased in the 10 degrees C environment over time. The differences that occurred at the various temperatures were believed to be related to fluid distribution in the muscle, muscle conduction velocity and sweating. The data imply that the EMG/force relationship measured using surface electrodes is influenced by ambient temperature.