DOI: 10.1249/mss.0000000000004052 ISSN: 0195-9131

High- and Low-Load Resistance Training Produce Distinct Skeletal Muscle Growth but Similar Changes in Tendon Morphology

William B. Hammert, Yujiro Yamada, Robert W. Sallberg, Enrique N. Moreno, Emily E. Metcalf, Evan W. Young, Ryo Kataoka, Jeremy P. Loenneke
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Purpose:

To compare the effects of high- versus low-load isotonic resistance training performed to task failure on skeletal muscle growth and distal biceps brachii tendon thickness, while incorporating a time-matched non-exercise control group.

Methods:

201 non-resistance trained individuals [20.9 (3.0) years] were randomly assigned to one of four groups: High-Load ( n =45), Low-Load ( n =48), Mid-Point ( n =54), or Control ( n =54). High- and Low-Load completed 4 sets of unilateral elbow flexions to task failure 3x/week for 6-weeks (8-12RM and 20-30RM, respectively). Mid-Point completed pre- and post-testing, plus a 1RM test at 3-weeks, whereas Control performed pre- and post-testing only. Muscle thickness of the elbow flexors and distal biceps brachii tendon thickness (short- and long-head regions) were assessed via B-mode ultrasound before and after the intervention. Group differences in pre- to post-intervention changes were evaluated using Bayesian ANCOVA with informative hypotheses, supplemented by Bayesian regression models to estimate adjusted between-group differences.

Results:

Low-Load produced greater increases in muscle thickness than High-Load (~0.30 cm versus ~0.20 cm), with both exceeding changes observed in Mid-Point and Control. In contrast, distal biceps brachii tendon thickness demonstrated small increases at the short-head across all training groups (High-Load, Low-Load, and Mid-Point; ~0.02-0.03 cm) relative to Control, whereas no detectable changes occurred at the long-head.

Conclusions:

When resistance exercise is performed to task failure, skeletal muscle and tendon tissues demonstrate distinct adaptation patterns; muscle growth may be augmented by low-load failure training, whereas tendon morphological adaptations may be driven more by localized strain exposure rather than the external load lifted per repetition.

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