Author(s): MUIRHEAD, P., ZAMBOLIN, F., MCPHEE, J., Institution: MANCHESTER METROPOLITAN UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 2782

INTRODUCTION:
Eccentric resistance training elicits pronounced neuromuscular and architectural adaptations, but delivering true eccentric overload is constrained by the concentric strength “bottleneck.” Adaptive Resistance Training Machines (ARTMs) use software-controlled, real-time load adjustment to facilitate eccentric overload, yet their efficacy for upper-limb strength and muscle architecture compared with traditional free-weight training remains unclear.
Purpose
To compare changes in eccentric elbow-flexor strength and biceps brachii architecture after 6 weeks of unilateral training with an ARTM versus traditional dumbbell loading.
METHODS:
Methods
Seventeen healthy adults (18–35 years) completed a 6-week unilateral elbow-flexor training intervention following baseline testing. For each participant, one arm trained with an ARTM implementing eccentric overload and the contralateral arm trained the same exercise with dumbbells without eccentric overload; arm–condition allocation (ARTM vs dumbbell) was counterbalanced between left and right. External load for dumbbell training was derived from elbow-flexor MVC by converting torque (N·m), calculated using forearm length, into an equivalent mass, and set at 50% of maximal eccentric MVC; the ARTM prescription was matched to this concentric load, with eccentric load progressed to 110–130% of concentric across the intervention. All repetitions were performed to a 60 bpm metronome to standardise movement tempo. Training was performed twice weekly for 6 weeks. Primary outcome was maximal eccentric elbow-flexor torque at 30°·s⁻¹, assessed bilaterally using isokinetic dynamometry. Secondary outcomes were biceps brachii fascicle length, pennation angle, and muscle thickness assessed by ultrasound. Two-way repeated-measures ANOVA (time × group) was conducted separately for each arm.
RESULTS:
Results
Eccentric MVC increased over time in both arms (right: F(1,15) = 20.09, p = 0.0004; left: F(1,15) = 53.68, p < 0.0001), with mean within-arm improvements of 7.6 ± 7.0 Nm (right) and 9.6 ± 6.1 Nm (left). A significant time × group interaction was observed for the left arm (F(1,15) = 5.72, p = 0.030), indicating a modest side-specific difference between training conditions, whereas no interaction was present for the right arm (p = 0.27). Fascicle length increased in both arms (right: F(1,15) = 21.58, p = 0.0003; left: F(1,15) = 19.23, p = 0.0005) and pennation angle also increased (right: F(1,15) = 7.03, p = 0.018; left: F(1,15) = 8.01, p = 0.013), with no significant time × group interactions for any architectural variable (all p ≥ 0.59). Muscle thickness did not change significantly in either arm (all time and interaction p ≥ 0.37).
CONCLUSION:
Conclusion
Unilateral elbow-flexor training with either ARTM-based eccentric overload or traditional dumbbells over 6 weeks produced significant gains in eccentric strength and increases in fascicle length and pennation angle, with largely similar adaptations between modalities. The isolated side-specific interact