Supplementary Material for: 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.

引言
疲劳耐力（Fatigue Resistance, FR）可定义为：受试者在持续最大自主收缩过程中，握力（Grip Strength, GS）降至其最大值50%时所用的时长。本研究首次比较了两种握力测试系统在疲劳耐力测试中的力-时间特性，并探究了年龄与临床相关的差异，以验证缩短版测试方案（即直至握力降至初始最大值的75%）是否具备足够的评估价值。

方法
本研究纳入了社区居住的青年健康人群（Y组，年龄<30岁，平均24±3岁，女性占比54%）、中年人群（MA组，年龄30~65岁，平均47±11岁，女性占比54%）、老年人群（OLD组，年龄>65岁，平均77±7岁，女性占比50%）以及住院患者（HOSP组，平均84±5岁，女性占比50%），所有受试者均完成疲劳耐力测试。
为此，本研究采用了两套测试系统：一是改装版握力计（将Martin Vigorimeter的原装橡胶球与Unik 5000型压力计相连，本研究中将其定义为“气动握力系统（Pneu）”）；二是Dynamometer G200系统（采用Jamar握力计的原装手柄，内置测力传感器，本研究中将其定义为“液压握力系统（Hydr）”）。
本研究对疲劳耐力测试过程中，初始最大握力从100%降至75%、以及从75%降至50%阶段的力-时间曲线进行分析。通过对每个时间间隔（即1/5000秒）内的实际握力进行积分，计算曲线下面积（Area Under the Curve, GW），并以受试者体重进行校正（GW/体重）。

结果
两套测试系统均显示，FR100-50与FR100-75之间存在尚可的相关性（气动系统：平均差值=50.1s，95%置信区间[47.9, 52.4]，r²=0.48；液压系统：平均差值=28.4s，95%置信区间[27.0, 29.7]，r²=0.52，所有p<0.001）；同时GW(100-50)/体重与GW(100-75)/体重之间也存在中等程度的相关性（气动系统：平均差值=32.1kPa·s/kg，95%置信区间[30.6, 33.6]，r²=0.72；液压系统：平均差值=8.1kg·s/kg，95%置信区间[7.7, 8.6]，r²=0.68，所有p<0.001）。
在中年组与老年组之间，采用气动系统测试时，前25%握力衰减阶段的GW值存在显著的年龄相关差异（中年组为10.2±0.6kPa·s/kg，老年组为7.1±1.2kPa·s/kg）。

讨论与结论
缩短版测试方案具备有效性。采用气动系统测试时，老年组与住院患者组在前25%握力衰减阶段的GW值存在显著差异，而液压系统测试未发现该差异。因此，在临床场景中，采用连续记录握力衰减的缩短版疲劳耐力测试方案可有效评估肌肉易疲劳性，但该结论仅适用于气动握力系统。