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Brent Raiteri, Leon Lauret, Daniel Hahn

• Residual force depression (rFD) following active muscle shortening is assumed to correlate most strongly with muscle work, but this has not been tested during voluntary contractions in humans. Using dynamometry, we compared steady-state ankle joint torques (\(\it N\) = 16) following tibialis anterior (TA) muscle–tendon unit (MTU) lengthening and shortening to the time-matched torque during submaximal voluntary fixed-end dorsiflexion reference contractions (REF) at a matched MTU length and EMG amplitude. Ultrasound revealed significantly reduced (\(\it P\) < 0.001) TA fascicle shortening amplitudes during MTU lengthening without a preload over small and medium amplitudes, respectively, relative to REF. MTU lengthening with a preload over a large amplitude significantly (\(\it P\) < 0.001) increased fascicle shortening relative to REF, as well as stretch amplitudes relative to MTU lengthening without a preload (\(\it P\) = 0.001). Significant (\(\it P\) = 0.028) steady-state fascicle force enhancement relative to REF was observed following MTU lengthening, and was similar among MTU lengthening-hold conditions (3–5%). MTU shortening with and without a preload over small and large amplitudes significantly (\(\it P\) < 0.001) increased positive fascicle and MTU work relative to REF, but significant (\(\it P\) = 0.006) rFD was observed following MTU shortening with a preload (7–10%) only. rFD was linearly related to positive MTU work [\(r_{rm}\)(47) = 0.48, \(\it P\) < 0.001], but not positive fascicle work [\(r_{rm}\)(47) = 0.16, \(\it P\) = 0.277]. Our findings indicate that MTU lengthening without substantial fascicle stretch enhances steady-state force output, which might arise from less shortening-induced rFD. Our findings also indicate similar rFD following different amounts of positive fascicle/MTU work, which cautions against using work to predict rFD during submaximal voluntary contractions.