Measurement of quadriceps strength in patients with COPD using a rig-supported handheld dynamometer

Background Quadriceps strength (QS) predicts prognosis in COPD. Measurement using a non portable isokinetic dynamometer (ID) is the gold standard. Handheld dynamometers (HHD) are portable, but measurements of QS obtained using unsupported HHD may be affected by operator strength. We therefore constructed a portable rig that can be bolted to a chair to support a HHD, and evaluated its performance in measurement of QS in COPD patients. Objectives To determine whether use of a rig to support a HHD reduces inter-observer variability in QS measurement, and generates data which correlate with those obtained using an ID. Methods Two operators (A-male, BMI 25.5 kg/m2; B-female, BMI 19.3 kg/m2) measured QS using unsupported HHD (12 patients) and rig-supported HHD (15 patients); values obtained for each patient were compared between operators. QS was then measured in 30 patients using both rig-supported HHD and ID; values obtained for each patient were compared between methods. Results Measurements of QS obtained using unsupported HHD differed between operator A vs. B (mean QS 49.5 kg vs 35.3 kg respectively; 95% CI for difference 5.9 to 22.6, p=0.003). Inter-observer variation was eliminated by use of the portable rig to support the HHD (mean QS 32.1 kg vs. 32.1 kg for operators A vs. B respectively; 95% CI for difference -1.4 to 1.5, p=0.96). Measures of QS using rig-supported HHD vs. ID were highly correlated (r = 0.92; 95% CI 0.76 to 0.97, p Conclusions Use of a portable rig to support a HHD in the measurement of QS in COPD patients eliminates observer effects, and generates values which correlate highly with those obtained using the gold standard methodology.