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.

Stimuli for Adaptations in Muscle Length and the Length Range of Active Force Exertion—A Narrative Review

“…Interestingly, both Franchi et al (2014) and Seger et al (1998) found regional hypertrophy in the central region of the VL ACSA (11%) and total quadriceps ACSA (3.4%) after CT, respectively. Increases in quadriceps muscle volume were also observed by Quinlan et al (2021) after only 4 weeks of submaximal CT performed for 8 weeks with a leg press in young (mean age: 23.3 years) and older males (mean age: 69.1 years).…”

“…In contrast, no change in Achilles tendon stiffness was reported after 6 weeks of a heel-drop regimen (Morrissey et al, 2011). In the previous studies, the Patella tendon CSA and length remained unchanged (Malliaras et al, 2013;Quinlan et al, 2021), while increases in Patella tendon CSA (+14.9%) were found after a 12-week CT performed with whey protein supplementation (Farup et al, 2014b).…”

“…There is evidence that concentric-only strength training (CT) leads to increases in muscle strength and enhanced muscle size as reported for several muscles (e.g., VL, quadriceps, biceps brachii) after 8-12 weeks of training (Higbie et al, 1996;Housh et al, 1996;Seger et al, 1998;Farthing and Chilibeck, 2003;Moore et al, 2012;Franchi et al, 2014;Farup et al, 2014b;Quinlan et al, 2021). For instance, Franchi et al (2014) found VL muscle volume increases of 8% after 10 weeks of CT and increases in VL ACSA in the muscle's mid and distal portions (11 and 2%, respectively).…”

“…After 12 weeks of CT, Patellar tendon stiffness and Young's modulus were reported to increase by 75.7% (Malliaras et al, 2013). Similarly, Patella tendon stiffness and Young's modulus were already significiantly increased after 4 weeks of CT in young as well as older males (Quinlan et al, 2021). Quinlan et al further showed that while the observed changes in tendon mechanical properties stayed constant in the young males, they continued to increase from week 4 to week 8 in the older males suggesting a delayed response.…”

“…Despite observed increases in VL fascicle lengths of 2% after 4 weeks of CT (Franchi et al, 2015) and around ~6% after 10 weeks of CT (Blazevich et al, 2007;Franchi et al, 2014), decreases in fascicle lengths of 11.8% and ~ 11.7% were reported for the biceps femoris and supraspinatus after the performance of isokinetic CT (Kim et al, 2015;Timmins et al, 2016). Regarding changes in fascicle PA after CT, studies consistently showed increases in the VL (ranging from 13-30%), biceps femoris (21.1%) and supraspinatus (~22.7%; Blazevich et al, 2007;Franchi et al, 2014;Kim et al, 2015;Timmins et al, 2016;Quinlan et al, 2021). In this context, Quinlan et al reported significant increases in VL PA already after 2 weeks of submaximal CT in both young and older males.…”