Reliability and Diurnal-Fatigability Effects on Force–Time Characteristics During Maximal Voluntary Handgrip Contractions

Single-effort isometric handgrip strength tests are widely used as a proxy of overall muscular strength. While using peak force (PF) is practical and meaningful, additional force-time characteristics could provide insight into muscle function. The purpose of this study was to assess test-retest reliability of force-time characteristics for maximal voluntary handgrip contractions (Analysis 1) and assess the influence of fatigability and time-of-day (Analysis 2). Nineteen participants completed Analysis 1 (23.5 ± 5.7 years, 168.7 ± 8.3 cm, 75.4 ± 14.0 kg) and 18 participants completed Analysis 2 (23.4 ± 5.9 years, 168.7 ± 10.4 cm, 77.6 ± 14.6 kg). For both analyses, participants completed three 4-s maximal voluntary handgrip contractions with 1-min rest periods. For Analysis 2, participants completed the maximal voluntary handgrip contractions before and after a fatiguing handgrip intervention at three separate times-of-day. Variables included PF, time to PF, time to 90% PF (TT90), area under the curve deficit (AUC Deficit), plateau force coefficient of variation, and plateau derivative root mean square. Using point estimates, all dependent variables demonstrated moderate-excellent relative reliability. A Time-of-day × Fatigability interaction was observed for TT90, AUC Deficit, and force coefficient of variation. Main effects of fatigability were observed for all variables, excluding plateau derivative root mean square. Time-of-day did not demonstrate an impact to any dependent variable. While task specific, an adequate warm-up may mitigate time-of-day impact to performance previously reported. TT90 and force maintenance variables, such as AUC Deficit, and force coefficient of variation, appear to be sensitive to the interaction between time-of-day and fatigability. Force maintenance variables may provide further insight beyond PF when examining maximal effort handgrip strength.