FURTHER IMPAIRMENT OF MUSCLE PHOSPHATE KINETICS BY LENGTHENING EXERCISE IN DMD BMD CARRIERS - AN IN-VIVO P-31-NMR SPECTROSCOPY STUDY

We used phosphorus magnetic resonance spectroscopy (P-31-MRS) to study the effect of exercise-induced muscle injury in the calf muscle of 7 DMD/BMD carriers and 6 non-carrier females. All subjects performed 50- 80 lengthening contractions with the right calf muscles. 48 h after le ngthening exercise non-carriers showed increased sensitivity to pressu re in their gastrocnemius accompanied by increased T2 relaxation times and by elevated P(i)/PCr ratios at rest. DMD/BMD carriers did not sho w any effect of lengthening exercise on these measurements. In-magnet exercise revealed in all carriers a reduced initial rate of P(i) recov ery and an increased time to fully recover the resting value of intrac ellular pH. Lengthening exercise further decreased the initial rate of P(i) recovery. Non-carriers did not show any variation attributable t o lengthening exercise either during in-magnet work or during recovery from exercise. We found that lengthening exercise contractions causes : (1) less muscle injury in carriers compared to non-carriers, (2) eve n slower rate of P(i) recovery, but (3) no effect on P(i) recovery in non-carriers. The use of lengthening exercise and measurements of P(i) recovery may be a useful method to evaluate the disease process in DM D/BMD.