Reliability and validity of trunk flexor and trunk extensor strength measurements using handheld dynamometry in a healthy athletic population.

OBJECTIVES

To investigate reliability and validity of handheld dynamometry (HHD) strength tests to accurately measure isometric trunk flexion and extension strength.

DESIGN

Test-retest design and comparative analysis to investigate reliability and validity respectively.

SETTING

Isometric trunk flexion and extension strength, measured with a handheld dynamometer, was compared to isometric strength testing on a stationary isokinetic dynamometer. Different test positions were examined for the HHD measurements for trunk flexion and extension strength.

MAIN OUTCOME MEASURES

Trunk muscle strength was calculated in newton metres (Nm) for both devices. Results of both devices were compared with Pearson correlations and agreement between both methods was explored with Bland-Altman plots. ICC values were calculated to assess HHD intra- and inter-tester reliability.

RESULTS

Reliability was good to excellent for all HHD tests (ICC = 0.67-0.93). High correlations were found between the HHD tests and stationary dynamometer tests (r = 0.65-0.86). Bland-Altman plots showed agreement between both methods for the trunk flexion test, supported in 30° trunk flexion and for the trunk extension test in a prone position in 0° trunk flexion.

CONCLUSION

Handheld dynamometry is reliable and a clinically applicable valid method to evaluate isometric trunk flexion and extension strength.