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


METHODS
Repeated-measures over a 3-week interval.


METHODS
University hospital.


METHODS
Convenience sample of 65 patients with PPS.


METHODS
Dynamometer testing.


METHODS
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.
Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam, The Netherlands. h.horemans@vumc.nl
Herwin L
HL
Horemans
Anita
A
Beelen
Frans
F
Nollet
David A
DA
Jones
Gustaaf J
GJ
Lankhorst
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D015982:Bias; D018450:Disease Progression; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D008875:Middle Aged; D018908:Muscle Weakness / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D026741:Physical Therapy Modalities / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D016262:Postpoliomyelitis Syndrome / Q000150:complications* / Q000175:diagnosis; D018401:Sample Size; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D013997:Time Factors; D019415:Torque