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Effects of resistance training on tendon mechanical properties and rapid force production in prepubertal children
1Centre for Sports Medicine and Human Performance, Brunel University, London, United Kingdom; and.
Insights
Resistance training improves Achilles tendon stiffness and reduces electromechanical delay in children. However, these adaptations did not significantly enhance the rate of force development, impacting movement efficiency.
Area of Science:
- Pediatric exercise science
- Musculoskeletal adaptation
- Biomechanics
Background:
- Children exhibit lower muscle force and rate of force production compared to adults.
- Strength training in children requires concurrent tendon adaptation for efficient force transmission and injury prevention.
Purpose of the Study:
- To investigate the effects of resistance training on Achilles tendon mechanical properties and electromechanical delay in prepubertal children.
- To determine if tendon adaptations influence force production characteristics.
Main Methods:
- A 10-week resistance training program involving plantar flexion exercises was administered to prepubertal children.
- Measurements included Achilles tendon properties (e.g., stiffness, Young's modulus), electromechanical delay (EMD), rate of force development (RFD), and rate of electromyographic increase (REI).
Main Results:
- Resistance training significantly increased Achilles tendon stiffness and Young's modulus in the training group.
- A significant decrease in electromechanical delay (EMD) was observed post-training, correlating with increased tendon stiffness.
- No significant changes were found in the rate of force development (RFD) or rate of electromyographic increase (REI).
Conclusions:
- The Achilles tendon adapts to resistance training in prepubertal children, showing increased stiffness and altered EMD.
- While tendon adaptations occur, they may not be sufficient to enhance the rate of force development in this age group.
- Findings highlight the importance of tendon adaptation for movement efficiency and injury risk management in pediatric resistance training.
Abstract:
Children develop lower levels of muscle force, and at slower rates, than adults. Although strength training in children is expected to reduce this differential, a synchronous adaptation in the tendon must be achieved to ensure forces continue to be transmitted to the skeleton with efficiency while minimizing the risk of strain-related tendon injury. We hypothesized that resistance training (RT) would alter tendon mechanical properties in children concomitantly with changes in force production characteristics. Twenty prepubertal children (age 8.9 ± 0.3 yr) were equally divided into control (nontraining) and experimental (training) groups. The training group completed a 10-wk RT intervention consisting of 2-3 sets of 8-15 plantar flexion contractions performed twice weekly on a recumbent calf-raise machine. Achilles tendon properties (cross-sectional area, elongation, stress, strain, stiffness, and Young's modulus), electromechanical delay (EMD; time between the onset of muscle activity and force), rate of force development (RFD; slope of the force-time curve), and rate of electromyographic (EMG) increase (REI; slope of the EMG time curve) were measured before and after RT. Tendon stiffness and Young's modulus increased significantly after RT in the experimental group only (∼29% and ∼25%, respectively); all other tendon properties were not significantly altered, although there were mean decreases in both peak tendon strain and strain at a given force level (14% and 24%, respectively; not significant) which may have implications for tendon injury risk and muscle fiber mechanics. A decrease of ∼13% in EMD was found after RT for the experimental group, which paralleled the increase in tendon stiffness (r = -0.59); however, RFD and REI were unchanged. The present data show that the Achilles tendon adapts to RT in prepubertal children and is paralleled by a change in EMD, although the magnitude of this change did not appear to be sufficient to influence RFD. These findings are of importance within the context of the efficiency and execution of movement.
