Effects of electromyostimulation training and home-based exercise on hamstring and quadriceps muscle strength and steadiness in older adults
Bezerra, P, Zhou, S, Crowley, Z & Baglin, R 2008, 'Effects of electromyostimulation training and home-based exercise on hamstring and quadriceps muscle strength and steadiness in older adults', International Convention on Science, Education and Medicine in Sport, Guangzhou, China, 1-5 August, ICSEMIS Organizing Committee, vol. 3, p. 337.
Resistance training has shown to delay or reverse the effects of ageing on neuromuscular function, with improvements in muscle strength and steadiness in force production. Electromyostimulation alone or superimposed over voluntary contraction (E-V) has been used in sport training and physiotherapy. However, its effect on control of force production in older adults has not been thoroughly examined. The aim of this study was to examine whether an E-V training would affect muscle strength (MVC) and steadiness (ST) differently to a home-based exercise (HBE) program, in older adults.
Sixty healthy volunteer participants, in age range of 60 to 77 years, were randomly allocated into three groups, with 10 males and 10 females in each of the control group (CG), HBE group (HBEG) and E-V group (E-VG). The training groups exercised 3 sessions per week for 6 weeks, while the CG maintained normal daily activities. Within each training session, E-VG performed 3 sets of 10 repetitions of isometric MVC in bilateral isometric knee extension and flexion exercises. The MVC was superimposed with electrical stimulation of 100 Hz at the intensity of maximal tolerance, with a duty cycle of 5 s contraction followed by 5 s rest and 1 min recovery between sets. The HBEG performed 3 sets of dynamic (sit and rise, leg curl) and isometric (push wall, hold ball between thigh and calf) exercises, each for 5 s, at moderate to strong intensity, with incremental number of repetitions (5 to 20), and 1 to 2 min recovery between sets and exercises. The MVC of quadriceps (Quads) and hamstrings (Hams) muscles was assessed in static knee extension and flexion, pre and post the 6-week training. ST was assessed under isometric conditions at 25% (ST25), 15% (ST15) and 5% (ST5) of MVC and quantified as absolute (standard deviation, SD) and normalized (coefficient of variation, CV) fluctuation of force. General linear model multivariate analysis with group and gender as fixed factors was performed to compare the between-group MVC and ST differences. Bivariate correlations were used to examine the relationship between MVC and ST in both muscles. Statistical significance was set at p < 0.05.
MVC increased significantly after training in Quads and Hams in both E-VG and HBEG. The interaction of time by group showed that the increase in HBEG (8.8% Quads) and E-VG (12.6% Quads, 16.9% Hams) were significantly greater than that in CG (2.1% Quads, 0.2% Hams). No significant training effects were found on the CV of Quads at all force levels, neither between- nor within-groups. In VG, males showed significantly greater Hams´ CV25 and CV15 than females before training but not after training. Males also showed significant greater SD than females, pre and post training, at all force levels in Quads and Hams. Moderate to strong correlations were found between Quads MVC and SD (r =0.49 to 0.67), and between Hams MVC and SD at ST25 and ST15 (r =0.28 to 0.34) pre and post training. No correlations were found between the training-induced changes in MVC and ST.
Both the E-V and HBE training programs were effective in increasing MVC and muscle steadiness of older adults. Males in general showed greater variations in submaximal force production than female counterparts, which was positively correlated to MVC. However, the training-improved performance in steadiness did not appear to be associated with the increased MVC in both males and females.