Reliability and validity of hand-held dynamometry for assessing lower limb muscle strength

BACKGROUND: Hand-held dynamometry (HHD) is used to assess muscle strength in various patient populations, but many variations in protocols exist. OBJECTIVE: First, to systematically develop a protocol of HHD for all lower limb muscle groups and evaluate intra-rater reliability; second, to validate HHD with fixed dynamometry for the knee flexor and extensor muscles. METHODS: Thirty healthy young adults (women: men - 15:15) participated in two testing sessions. HHD of 12 lower limb muscle groups was performed in both sessions, while fixed dynamometry of knee muscle groups was performed only in the second session. RESULTS: The intra-rater reliability of HHD was good for five muscle groups and excellent for seven muscle groups (ICC3, k = 0.80-0.96). The criterion validity of HHD ranged from very good to excellent for the knee flexors (r = 0.77-0.89) and from good to very good for the knee extensors (r = 0.65-0.78). However, peak moment values for the knee extensor muscles were underestimated by 32% (p < 0.001). CONCLUSIONS: The proposed HHD protocol provides reliable and valid measurements of lower limb muscle isometric strength in healthy adults, which may also be used to test patients with mild muscle strength deficits. However, possible underestimation of absolute strength must be considered when interpreting the results of knee extensors or other large muscles.