Comparison between two different handgrip systems and protocols on force reduction in handgrip assessment

INTRODUCTION Fatigue resistance (FR) can be assessed as the time during which grip strength (GS) drops to 50% of its maximum during a sustained maximal voluntary contraction. For the first time we compared force-time characteristics during FR test between two different handgrip systems, and investigated age- and clinical-related differences in order to verify if a briefer test protocol (i.e. until 75%) could be sufficiently informative. METHODS A cohort of young healthy (Y, <30y, 24±3y, 54% women), middle-aged (MA, 30-65y, 47±11y, 54% women) and older (OLD, >65y, 77±7y, 50% women) community-dwelling persons, and hospitalized patients (HOSP, 84±5y, 50% women) performed the FR test. For this purpose, an adapted Vigorimeter (original rubber bulb of the Martin Vigorimeter connected to a Unik 5000 pressure gauge) here defined as "pneumatic handgrip system" (Pneu) and Dynamometer G200 system (original Jamar Dynamometer handle with an in-build strength gauge) here defined as "hydraulic handgrip system" (Hydr) were used. Force-time curves were analysed from 100%-75% and from 75%-50% of the initial maximal GS during the FR test. The area under the curve (GW) was calculated by integrating the actual GS at each time interval (i.e. 1/5000s) and corrected for body weight (GW/body weight). RESULTS For both systems we found fair associations between FR100-50 and FR100-75 (Pneu mean difference=50.1s (95%CI:47.9-52.4), r2=0.48; Hydr mean difference=28.4s (95%CI:27.0-29.7), r2=0.52, all p<0.001), and also moderate associations between GW(100-50)/body weight and GW(100-75)/body weight (Pneu mean difference=32.1kPa*s/kg (95%CI:30.6-33.6), r2=0.72; Hydr mean difference = 8.1kg*s/kg (95%CI:7.7-8.6), r2 = 0.68, all p<0.001). Between MA and OLD we found a significant age-related difference in the GW results in the first 25% strength decay for Pneu (respectively 10.2±0.6kPa*s/kg against 7.1±1.2kPa*s/kg). DISCUSSION/CONCLUSION The brief test protocol is valid. Differences within the first 25% strength decay in GW between OLD and HOSP were identified when using Pneu, but not when using Hydr. Therefore, a brief FR test protocol using a continuous registration of the strength decay seems to be sufficiently informative in a clinical setting to appraise muscle fatigability, however, only when using a Pneu system.