RESUMEN
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 controls (Y, <30 y, 24 ± 3 y, 54% women), middle-aged (MA, 30-65 y, 47 ± 11 y, 54% women), and older (OLD, >65 y, 77 ± 7 y, 50% women) community-dwelling persons, and hospitalized geriatric patients (HOSP, 84 ± 5 y, 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% to 75% and from 75% to 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., 1/5,000 s) 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 = 50.1 s [95% CI: 47.9-52.4], r2 = 0.48; Hydr mean difference = 28.4 s [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 = 32.1 kPa*s/kg [95% CI: 30.6-33.6], r2 = 0.72; Hydr mean difference = 8.1 kg*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 (10.2 ± 0.6 kPa*s/kg against 7.1 ± 1.2 kPa*s/kg, respectively). 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.
RESUMEN
BACKGROUND: Fatigue resistance (FR) was here defined as the time during which grip strength (GS) drops to 50% of its maximum during sustained contraction. Since different GS systems exist, we compared FR obtained with Pneumatic (Pneu) and Hydraulic (Hydr) handgrip systems. Hand pain induced by both systems was also investigated since this might influence FR-outcomes. METHODS: 618 young controls (Y: reference group), 426 middle-aged (MA) and 234 old community-dwelling adults (OLD), and 50 hospitalized patients (HOSP) participated. FR was recorded with Pneu and Hydr. Grip work corrected for body weight (area under the strength-time curve; GWBW = 0.75 ∗ maximal GS ∗ FR / body weight) was calculated. We corrected for body weight since heavier or more obese participants will have to engage more strength and sustain the effort over time. Thereafter GWBW was expressed as T-scores representing the deviation from the mean score of the sex-specific reference group. Experienced pain, its intensity and whether pain hindered participants to sustain the contraction were questioned. RESULTS: Overall, although significant correlation between FR measured with both systems was found (r = 0.418, p < 0.001), FR measured by Pneu (55.7 ± 35.0 s) was higher compared to Hydr (34.2 ± 18.4 s). There was a proportional difference in FR measured with both systems (R2 = 0.36, p < 0.001), highlighting the longer participants could sustain FR test, the higher the difference in FR measured with both systems. Overall, there was no difference in pain variables between both systems. Independent of sex and system, GWBW deviated less from reference group in MA compared to OLD and HOSP. In OLD, GWBW deviated less from reference group than HOSP, independent of sex and system. CONCLUSION: Participants were unable to sustain the contraction with Hydr as long as with Pneu. Hydr seems less able to identify subjects with higher levels of muscle endurance. Based on the GWBM-scores we can conclude that either system can be used for assessing muscle fatigability, but Pneu may be more sensitive as differences can be detected more easily.
