Normalized force, activation, and coactivation in the arm muscles of young and old men

Abstract

The purpose of this study was to determine whether the loss of muscle strength in the elderly could be explained entirely by a decline in the physiological cross-sectional area (PCSA) of muscle. Isometric force, muscle activation (twitch interpolation), and coactivation (surface electromyograph) were measured during maximal voluntary contractions (MVCs) of the elbow flexors (EFs) and extensors (EEs) in 20 young (23 +/- 3 yr) and 13 older (81 +/- 6 yr) healthy men. PCSA was determined using magnetic resonance imaging, and normalized force (NF) was calculated as the MVC/PCSA ratio. The PCSA was smaller in the old compared with the young men, more so in the EEs (28%) compared with the EFs (19%) (P < 0.001); however, the decline in MVC (approximately 30%) with age was similar in the two muscle groups. Muscle activation was not different between the groups, but coactivation was greater (5%) (P < 0.001) in the old men for both muscles. NF was less (11%) in the EFs (P < 0.01) and tended to be unchanged in the EEs of the old compared with young subjects. The relative maintenance of NF in the EEs compared with the EFs may be related to age-associated changes in the architecture of the triceps brachii muscle. In conclusion, although the decline in PCSA explained the majority of strength loss in the old men, additional factors such as greater coactivation or reduced specific tension also may have contributed to the age-related loss of isometric strength.

Physiological elevation of endogenous hormones results in superior strength training adaptation

“…The findings of increased CSA at the part of elbow flexors with largest CSA in L+A could be due to the acute elevation of anabolic hormones during the strength training. Furthermore, it has been observed that the largest CSA of a muscle determines the maximum strength of the muscle (Bamman et al 2000;Klein et al 2001), and consequently the increase in CSA in the L+A arm is the likely mechanism behind the superior 1RM improvement in L+A. The findings of increased CSA and strength after strength training without any acute elevations in circulatory hormones are in agreement with the findings of Wilkinson et al (2006).…”

Age-related differences in pre-movement antagonist muscle co-activation and reaction-time performance

“…They also reported a similar increase in M. Triceps Brachii co-activation during elbow flexion in their elderly participants (Klein et al, 2001). Contrary to their findings, in our study the coactivation of the M. Triceps Brachii during elbow flexion was equal in both groups and comparable to the co-activation level of the M Biceps Brachii during elbow extension in the young subjects.…”

“…In the elderly subjects we observed a significantly higher M. Biceps Brachii co-activation during maximal isometric extension of the elbow compared to the young ones (8±3% higher, p<0.01). Also Klein et al reported a +/-5% higher M. Biceps Brachii co-activation in elderly compared to young subjects during maximal isometric elbow extension (Klein et al, 2001). …”

“…Higher antagonist co-activation has been reported in elderly persons for both isometric and dynamic contractions (Izquierdo et al, 1999;Klein et al, 2001;Macaluso et al, 2002). It is assumed that this might be a physiologic compensation for age-related muscle weakness in order to increase joint stiffness and maintain joint stability (Hortobagyi and DeVita, 2000).…”

Mentally represented motor actions in normal agingI. Age effects on the temporal features of overt and covert execution of actions

“…It is well known that normal aging influences cognitive functions [2,13,24,40,41] and sensorimotor control of actions [22,43,44]. The state of musculoskeletal system, in particular that of muscular mechanics and structure, is also modified [17,23,26,32,46,47,49]. At the neural level, clear differences emerge when comparing brain's activation between elderly and young people during the performance of motor or cognitive tasks.…”