Isometric Measurement of Hamstrings and Quadriceps Strength in Multiple Sclerosis Patients: Sensitivity and Variability

The use of mechanized testing of quadriceps and hamstrings strength in isometric contraction in multiple sclerosis patients has not been previously reported. To determine the utility of such testing in clinical trials, two studies were carried out First, to assess variability both within a testing session and between testing sessions, twenty-four MS patients with leg weakness that had been stable for at least two months were evaluated every eight weeks over a sixteen-week period. Quadriceps and hamstrings strength were measured in isometric contraction in triplicate at each testing session. The intraclass correlation coefficient for the mean strength determinations done every eight weeks for sixteen weeks was 0.99 and the coefficients of variation were 7.81 +/- 6.97% for hamstrings and 5.97 +/- 4.03% for quadriceps. Only four series of determinations out of eighty-six had coefficients of variation greater than 20%. In the second study, patients undergoing symptomatic treatment with an experimental drug, 4-aminopyridine, were rested to determine whether treatment-related changes were seen, and these changes were compared with the results of conventional manual muscle strength testing. Isometric test results appeared to be more sensitive to drug-related changes than manual motor testing. These results suggest that quantitative isometric strength testing may be useful in clinical trials of MS patients.