Effect of varying the ratio of electrically induced muscle contraction time to rest time on serum creatine kinase and perceived soreness.

Supported in part by a North Carolina Physical Therapy Association Student Research Grant. The purpose of this study was to determine whether there were differences in the amount of muscle soreness and serum creatine kinase (CK) produced when ratios of electrically induced muscle contraction time to rest time were varied. Fifteen subjects were randomly assigned to one of three groups, each receiving 10, 15-second electrically induced isometric contractions of the quadriceps femoris muscle with rest periods of 10, 30, and 50 seconds between contractions, respectively. The intensity of the contractions were maintained at 30 percent of an individual's maximum voluntary isometric contraction (MVC). Blood samples for serum CK activity, an indicator of muscle damage, and perceived soreness were collected pretreatment, 24, 48, and 72 hours following the single treatment session. Significant increases in the serum CK and perceived soreness ratings were observed in all groups. Postexercise serum CK increases were found to be significantly different between the 10 seconds and the 30-seconds and 50-seconds rest period groups. Clinically, muscle soreness may result from initial trials of neuromuscular electrical stimulation (NMES) with peak amplitudes sufficient to produce contractions equivalent to 30 percent of the MVC. Contraction time to rest ratios of NMES may influence the amount of muscle damage produced. J Orthop Sports Phys Ther 1991,13(6):310-315.