Reproducibility of maximal quadriceps strength and its relationship to maximal voluntary activation in postpoliomyelitis syndrome

Horemans, Herwin L., Beelen, Anita, Nollet, Frans, Jones, David A. and Lankhorst, Gustaaf J. (2004) Reproducibility of maximal quadriceps strength and its relationship to maximal voluntary activation in postpoliomyelitis syndrome. Archives of physical medicine and rehabilitation, 85 (8). pp. 1273-8. ISSN 0003-9993

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Abstract

OBJECTIVES: To determine what changes in maximal isometric strength can be detected in a symptomatic quadriceps muscle in patients with postpoliomyelitis syndrome (PPS) and to investigate the association between the variability in maximal strength and maximal voluntary activation (MVA). DESIGN: Repeated-measures over a 3-week interval. SETTING: University hospital. PATIENTS: Convenience sample of 65 patients with PPS. INTERVENTION: Dynamometer testing. MAIN OUTCOME MEASURES: Maximal voluntary contraction (MVC) torque of the quadriceps was measured with a Kin-Com dynamometer and MVA was determined by twitch interpolation. RESULTS: The mean difference between the 2 consecutive measurements was -0.7+/-12.8 Nm (95% confidence interval [CI], -3.9 to 2.5). The test-retest reliability was excellent for MVC torque (intraclass correlation coefficient [ICC]=.96; 95% CI,.93-.98) and moderate for MVA (ICC=.73; 95% CI,.56-.85). The smallest detectable change in MVC torque was 25% for an individual. The variability in MVA explained 18% of the variability in maximal strength. CONCLUSIONS: Variability in maximal quadriceps strength, measured with a fixed dynamometer, was large and partly related to variability in MVA. This implies that even with optimally standardized strength testing, a follow-up of many years is required to objectify progression of quadriceps weakness in an individual patient with PPS. To demonstrate changes in strength in groups of patients in follow-up or intervention studies, feasible sample sizes are required.