Recovery of muscular performance by rewarming exercise in the cold

The effect of exercise on muscular performance and EMG-activity of the cooled lower leg muscles was studied. Eight voluntary male subjects (age 26 +/- 4 years (mean +/- SD), weight 72 +/- 6 kg, height 175 +/- 8 cm and body fat 15 +/- 3%) dressed in shorts and jogging shoes participated in the study. They were exposed to 27 degrees C and 10 degrees C for 60 min. After the 60 min exposure to 27 degrees C the subjects performed two maximal drop-jumps (stretch-shortening cycle) from a 40 cm bench onto a force plate. The flight time was analysed and the jump with longer flight time was chosen as thermoneutral reference. Also the duration of the contact phase, force production, takeoff velocity and the electromyographic activity (EMG) of the working agonist-antagonist muscle pair (m. triceps surae and m. tibialis anterior) were measured. After the exposure to 10 degrees C the subjects performed one drop-jump. To study the effect of exercise on the performance the subjects were thereafter allowed to walk on a treadmill at 10 degrees C for 5 min with a speed of 1.4 m . s(-1) (5 km . h(-1)) and after each walking bout they repeated the drop-jump. This cycle was repeated until the thermoneutral reference value in the flight time was achieved. One subject reached the thermoneutral flight time value after three walking bouts, four subjects after four bouts and three subjects after five bouts. Thermoneutral level in the duration of the contact phase, average force production during shortening and takeoff velocity were attained at the latest after the fifth walking bout. Muscle (m. gastrocnemius medialis) temperature was returned to thermoneutral level on the average after two walking bouts. Calf and shin skin temperatures rose significantly along the walking bouts but did not reach thermoneutral level. The walking bouts did not affect mean skin or rectal temperature. When compared to EMG-activity at 27 degrees C during the shortening phase, cooling decreased the integrated EMG-activity (IEMG) and mean power frequency (MPF) of the agonist muscle but increased the IEMG-activity of the antagonist muscle. These changes vanished along with repetitive walking bouts and thermoneutral level of EMG-activity was gained. It is concluded that a relatively small amount of low intensity exercise is required to recover muscle temperature, muscular performance and EMG-activity of the cooled muscles. The reversible changes in EMG-activity of the agonist-antagonist muscle pair correlated with the increased force production and thus increase in the flight time.