Author(s): KAY, A., BAROSS, A., BAXTER, B., BLAZEVICH, A., Institution: THE UNIVERSITY OF NORTHAMPTON, Country: UNITED KINGDOM, Abstract-ID: 1002

INTRODUCTION:
Chronic increases in joint range of motion (ROM) are usually achieved through various muscle stretching modes, however a recent meta-analysis revealed large increases (g = 0.86) in ROM after eccentric resistance training programmes [1]. While the chronic effects of eccentric training have been examined, the acute and repeated bout effects on ROM and muscle-tendon mechanics remain unknown. Therefore, the present study compared the acute and repeated bout effects of static stretching and eccentric contractions on plantarflexor ROM and muscle-tendon mechanics.
METHODS:
Using a randomised, crossover design, 18 recreationally active subjects completed four trials under two experimental conditions (static stretches [SS1, SS2]; eccentric contractions [EC1, EC2]), with each trial separated by 48-72 h. During SS trials, participants performed 5 sets of 30-s static stretches, whilst EC trials consisted of 5 sets of 10 repetitions of 3-s isokinetic eccentric contractions (total loading matched at 150 s). Before and after the trials, passive dorsiflexion ROM and passive gastrocnemius medialis and Achilles tendon stiffness were recorded using isokinetic dynamometry and ultrasonography.
RESULTS:
Acute effects: Significant increases in ROM (SS1 = 2.2 ± 2.9°, d = 0.76; EC1 = 6.0 ± 3.6°, d = 2.00) and decreases in muscle stiffness (SS1 = 10.7 ± 14.5% [0.17 ± 0.28 Nm·mm-1], d = 0.59; EC1 = 6.1 ± 22.2% [0.15 ± 0.40 Nm·mm-1], d = 0.38) occurred after the initial trials in both conditions, with Achilles tendon stiffness also reduced after the EC1 condition (12.0 ± 9.2% [0.91 ± 0.79 Nm·mm-1], d = 1.15). Repeated bout effects: Baseline ROM was significantly greater after two bouts of eccentric contractions (7.1 ± 4.6°, d = 1.55) whereas no significant change occurred after two bouts of static stretching. No significant change occurred after two bouts of either condition for baseline muscle stiffness or tendon stiffness.
CONCLUSION:
The greater (~threefold mean increase) acute increases in ROM following eccentric contractions and concomitant reductions in muscle (both conditions) and tendon stiffness (eccentric contraction condition only) may have important practical implications for warm-up design. Furthermore, the significant increase in baseline ROM after only two bouts (i.e. 1 week) of eccentric contractions also demonstrate the potential for a more rapid adaptive profile than muscle stretching (i.e. current practice), data consistent with large increases in ROM reported after as few as four weeks of eccentric training [2,3]. Collectively, these data indicate that eccentric contractions may deliver a more potent stimulus to increase ROM by influencing muscle and tendon stiffness simultaneously than current muscle stretching techniques.

References
1. Kay et al. (2023). Med Sci Sport Exerc. 55(4):710-21.
2. Aune et al. (2019). J Sports Sci. 37(2):138-45.
3. Leslie et al. (2017). Appl Physiol Nutr Metab. 42(10):1044-53.