Author(s): TECCHIO, P., RAITERI, B.J., HAHN, D., Institution: RUHR UNIVERSITY BOCHUM, Country: GERMANY, Abstract-ID: 2226

INTRODUCTION:
Adaptations of the muscle-tendon unit to concentric (CON) versus eccentric (ECC) training remain debated. Surprisingly, CON and ECC training has not yet been compared in a randomized controlled trial [1] and previous research lacked appropriate mechanical matching of CON and ECC training. Further, only 2D ultrasound (US) has been used to evaluate architectural adaptations and no studies investigated adaptations to the aponeurosis despite its crucial role in force transmission. Thus, we conducted a randomized controlled trial comparing CON and ECC training adaptations following comparable mechanical training stimuli using a torque-angle-time matching strategy. Tibialis anterior (TA) adaptations were assessed based on changes to its force-length relation (FLR), muscle architecture and central aponeurosis properties quantified by freehand 3DUS.
METHODS:
Twenty-three participants were randomly allocated to a control (CTRL, N = 10; 6W; 26±3yr [mean±SD]; 67.4±8.3kg; 174±8cm) or training group (N = 13; 5W; 26±2yr; 71.6±10.7kg; 175±9cm). The training group completed an 8-week contralateral intervention, with CON and ECC training randomly assigned to the legs. Training and assessments were done on a dynamometer with participants seated in a reclined position (~70° backrest, 90° knee flexion) and the foot secured to a modified footplate attached to the crank arm. 3DUS tests were conducted in a supine position with the knee near full extension. During each training session, participants received real-time torque feedback and were asked to match predefined torque-angle-time traces that progressively changed. Ankle joint kinematics were constrained by the dynamometer and activation timing was set to result in active fascicle shortening (CON) and lengthening (ECC) only. FLRs were derived from five ankle angles (5° dorsiflexion (DF) to 35° plantar flexion (PF) in 10° increments; 0° = 90° between footplate and tibia). Muscle architecture and central aponeurosis properties were quantified by 3DUS at three ankle angles (5° DF, 15° and 35° PF) during fixed-end contractions at 0, 30, and 60% of the maximal muscle force determined pre-training.
RESULTS:
Linear mixed-effects models revealed significant but similar strength gains of ~7% following CON and ECC training relative to CTRL. Also, active fascicle lengths increased similarly following CON and ECC training relative to CTRL, resulting in a rightward shift of TA’s FLR. Both aponeurosis length and apparent aponeurosis stiffness did not significantly change in any group over time.
CONCLUSION:
This study provides the first randomized controlled trial evidence that mechanically matched CON and ECC training resulted in comparable strength gains and architectural and aponeurosis adaptations. This disagrees with previous research showing greater strength gains following ECC training. Consequently, contraction type does not seem to stimulate specific mechanical or morphological adaptions.

[1] A. J. Blazevich et al.,2026, JSHS,10.1016/j.jshs.2025.101090