Muscle strength and muscle characteristics in monozygous and dizygous twins.

Muscle strength and electrical activity were investigated on 31 pairs of young male and female monozygous (MZ) and dizygous (DZ) twins. The measurements included leg forces, force-time, running velocity, muscular power, maximal integrated electromyographic activity (IEMG) and chronaximetry of the quadriceps muscle group. In each parameter the intrapair variance was computed and the differences were tested between the MZ and DZ twins. The variance ratio (MZ vs. DZ) was statistically significant only for muscular power confirming an earlier finding which has demonstrated a genetic component for the variable. In addition to the various performance variables several key enzymes involved in ATP turnover during muscle contraction and in glucose residue metabolism were analyzed from the muscle biopsy samples (m. vastus lateralis). A genetic component could not be observed in any of their activities or their relationships to performance variables.