Key result
Active muscle shortening immediately preceding stretch significantly reduced residual force enhancement compared to pure stretch (11.4% vs 20.6%), an effect that was abolished with a 1-second pause or slower stretch speeds.
Absolute Event Rate: 11.4% vs 20.6%
p-value: p=<0.05
Residual force enhancement following active muscle shortening is time- and speed-dependent, suggesting mechanisms related to cross-bridge recovery or passive structural elements like titin.
Questions the magnitude of residual force enhancement during physiological contractions; leaves open its role in cardiac or skeletal muscle performance.
The steady-state isometric force following active muscle shortening or lengthening is smaller (force depression; FD) or greater (residual force enhancement; RFE) than a purely isometric contraction at the corresponding length. The mechanisms underlying these phenomena are not explained within the context of the cross-bridge theory and are rarely studied in concert. Previous studies have shown RFE to be speed-independent. In the present study, we investigated if RFE preceded by active shortening is time-dependent by electrically evoking RFE in the human adductor pollicis muscle. The results shown that a slow stretch following FD fully re-established RFE compared to higher speeds of stretch. The mechanism(s) responsible for the recovery of RFE following a preceding shortening contraction (FD) might be associated with the recovery of cross-bridge based force and/or the re-engagement of a passive structural element (titin). Voluntary interaction with one's environment involves highly coordinated shortening and lengthening muscle contractions. Therefore comprehending these history-dependent muscle properties in the context of movement control is paramount in understanding the behavior of in vivo motor control.
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Fortuna et al. (2016) studied Healthy (n=24). Active muscle shortening immediately preceding stretch vs. Pure stretch without preceding shortening was evaluated on Steady-state isometric residual force enhancement (RFE) (p=<0.05). Active muscle shortening immediately preceding stretch significantly reduced residual force enhancement compared to pure stretch (11.4% vs 20.6%), an effect that was abolished with a 1-second pause or slower stretch speeds.
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