Muscle and tendon adaptations to moderate load eccentric vs. concentric resistance exercise in young and older males

Abstract

Resistance exercise training (RET) is well-known to counteract negative age-related changes in both muscle and tendon tissue. Traditional RET consists of both concentric (CON) and eccentric (ECC) contractions; nevertheless, isolated ECC contractions are metabolically less demanding and, thus, may be more suitable for older populations. However, whether submaximal (60% 1RM) CON or ECC contractions differ in their effectiveness is relatively unknown. Further, whether the time course of muscle and tendon adaptations differs to the above is also unknown. Therefore, this study aimed to establish the time course of muscle and tendon adaptations to submaximal CON and ECC RET. Twenty healthy young (24.5 ± 5.1 years) and 17 older males (68.1 ± 2.4 years) were randomly allocated to either isolated CON or ECC RET which took place 3/week for 8 weeks. Tendon biomechanical properties, muscle architecture and maximal voluntary contraction were assessed every 2 weeks and quadriceps muscle volume every 4 weeks. Positive changes in tendon Young's modulus were observed after 4 weeks in all groups after which adaptations in young males plateaued but continued to increase in older males, suggesting a dampened rate of adaptation with age. However, both CON and ECC resulted in similar overall changes in tendon Young's modulus, in all groups. Muscle hypertrophy and strength increases were similar between CON and ECC in all groups. However, pennation angle increases were greater in CON, and fascicle length changes were greater in ECC. Notably, muscle and tendon adaptations appeared to occur in synergy, presumably to maintain the efficacy of the muscle-tendon unit.

Keywords: Ageing; Eccentric; Muscle; Submaximal RET; Tendon.

Fig. 1

Time course of the patellar tendon biomechanical adaptation in response to submaximal CON (A, C, E) or ECC RET (B, D, F). N values for groups were as follows: YC, n = 10; YE, n = 9; OC, n = 8; and OE, n = 8. P values for time point vs baseline in respective group * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001. P values for week 4 vs week 8 in respective group, ## P < 0.01. P values for young vs old at respective time point §§ P < 0.01, §§§ P < 0.001

Fig. 2

Time course of quadriceps’ muscle volume adaptation in response to submaximal CON (A + C) or ECC (B + D) RET. N values for groups were as follows: YC, n = 10; YE, n = 10; OC, n = 8; and OE, n = 8. P values for time point vs baseline in respective group * P < 0.05, ** P < 0.01, *** P < 0.001. P values for week 4 vs week 8 in respective group, # P < 0.05, ## P < 0.01. P values for CON vs ECC in respective age group and time point ¥ P < 0.05

Fig. 3

Time course of the vastus lateralis fascicle length adaptation in response to submaximal CON (A + C) or ECC (B + D) RET. N values for groups were as follows: YC, n = 10; YE, n = 9; OC, n = 8; and OE, n = 9. P values for time point vs baseline in respective group * P < 0.05, **** P < 0.0001. P values for week 4 vs week 8 in respective group, # P < 0.05. P values for young vs old at respective time point § P < 0.05

Fig. 4

Time course of the vastus lateralis pennation angle adaptation in response to submaximal CON (A + C) or ECC (B + D) RET. N values for groups were as follows: YC, n = 10; YE, n = 9; OC, n = 8; and OE, n = 9. P values for time point vs baseline in respective group * P < 0.05, ** P < 0.01, *** P < 0.001. P values for week 4 vs week 8 in respective group, # P < 0.05. P values for young vs old at respective time point §§§§ P < 0.0001

Fig. 5

Time course of knee extension MVC_peak adaptation in response to submaximal CON (A + C) or ECC (B + D) RET. N values for groups were as follows: YC, n = 10; YE, n = 10; OC, n = 8; and OE, n = 9. P values for time point vs baseline in respective group * P < 0.05. P values for P values for young vs old at respective time point § P < 0.05, §§ P < 0.01

Fig. 6

The angle–torque relationship in YC (A) and YE (B) at week 0 and week 8. N values for groups were as follows: YC, n = 10; YE, n = 9. P values between week 0 and week 8 in respective group * P < 0.05