Effects of six weeks isokinetic eccentric training (and detraining) on plantarflexor muscle-tendon mechanics in older adults

Introduction: Joint range of motion (ROM) is compromised as a result of ageing and in numerous neurological conditions where muscle stretching techniques often provide limited improvements in flexibility [1]. However, large increases in ROM (10-15°) with concomitant increases in muscle strength have been reported in young adults after eccentric-only training programmes [2,3]. Therefore, the present study examined the impact of a 6-week isokinetic eccentric plantarflexor and dorsiflexor training programme (and 8 weeks of detraining) on a range of musculoskeletal characteristics in older adults.

Methods: Maximal isometric and eccentric plantarflexor torque, Achilles tendon and gastrocnemius medialis (GM) stiffness, GM architecture, and dorsiflexion ROM were measured in 11 participants (age [mean ± SD] = 67.4 ± 5.6 y, mass = 70.5 ± 15.6 kg, height = 1.6 ± 0.1 m) before and after the 6-week training programme using dynamometry and sonography. All measures were then re-examined 8 weeks later to quantify detraining effects. Training was performed twice weekly, which consisted of 5 sets of 12 maximal plantarflexor and dorsiflexor isokinetic eccentric contractions, performed at a velocity of 10°·s-1 through 20° plantarflexion to 10° dorsiflexion ROM.

Results:Significant (P < 0.05) increases in isometric (22.4 ± 19.5%) and eccentric (40.1 ± 15.3%) plantarflexor strength, Achilles tendon stiffness (20.4 ± 6.2%), GM thickness (8.5 ± 5.5%) and fascicle length (7.8 ± 6.1%), alongside decreases in MTU (16.4 ± 16.0%) and GM (22.9 ± 19.5%) stiffness were detected immediately after the 6-week training programme. No change in GM pennation angle (0.1 ± 0.8° [0.8 ± 4.6%]) was detected. Eight weeks later, no significant regression in any measure was detected, which remained significantly different to baseline.

Conclusion:The concomitant improvements in ROM, tendon stiffness, muscle strength and size after eccentric exercise, with limited regression eight weeks after the cessation of training, is indicative of substantive and prolonged functional benefit. As eccentric-only exercise has a lower metabolic cost and perceived exertion than other contraction modes [4], it is ideally suited to older adults where cardiovascular comorbidity may limit exercise tolerance. Thus, as older adults are prone to musculoskeletal decline and periods of inactivity, these findings have important implications for clinical exercise prescription.

References
1. Katalinic et al. (2011). Phys Ther. 91(1):11-24.
2. Kay et al. (2016). Med Sci Sport Exerc. 48(7):1388-1396.
3. Nelson & Bandy (2004). J Athl Train. 39(3): 254-258.
4. LaStayo et al. (1999). Am J Physiol. 276(2):611-615.