Muscle fatigability measured with Pneumatic and Hydraulic handgrip systems are not interchangeable

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.

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; GW_BW = 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 GW_BW 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.

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, GW_BW deviated less from reference group in MA compared to OLD and HOSP. In OLD, GW_BW deviated less from reference group than HOSP, independent of sex and system.

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 GW_BM-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.