Thigh anthropometric changes in response to six weeks of voluntary and electromyostimulation-superimposed voluntary training in young men
Zhou, S, Bezerra, P & Crowley, Z 2008, 'Thigh anthropometric changes in response to six weeks of voluntary and electromyostimulation-superimposed voluntary training in young men', International Convention on Science, Education and Medicine in Sport, Guangzhou, China, 1-5 August, ICSEMIS Organizing Committee. p. 138.
It is known that several weeks of unilateral voluntary contraction (VC) and electromyostimulation (EMS) can induce strength gain not only in the exercised limb, but also in the unexercised contralateral limb. The muscle strength gain can be due to either an improved neural control or increased muscle cross sectional area (CSA), or a combination of the two. In the literature various methods and techniques have been employed in assessment of muscle CSA, however, magnetic resonance imaging (MRI) technique has been regarded as the golden standard. The aims of this study were to determine CSA of thigh muscles and fats using MRI technique, and to assess the relationships between the changes in muscle CSA, thigh circumference and skinfold, and strength gain, in the trained limb and unexercised contralateral limbs in response to six weeks of unilateral VC or EMS-superimposed-on-VC (E-V) training.
Thirty-one healthy male subjects, in age range of 18-33 years and without resistance training in the past six months, were randomly assigned into control (CG, n=10), voluntary training (VG, n=10) and E-V training (E-VG, n=11) groups. The VG and E-VG groups followed a program consisting of 30 maximal contractions per session, three sessions per week for six weeks, isometric knee extension training on the right leg, while the CG maintained normal daily activities. The maximal voluntary contraction (MVC) torque in knee extension and the anthropometric measurements were taken pre and post training. The anthropometric measurements were taken at mid-thigh, and 5 cm above (upper) and 5 cm below (lower) the mid-thigh levels, including CSA of the thigh (CSA-thigh), quadriceps muscle (CSA-quadriceps), and fat (CSA-fat), assessed by MRI analysis; thigh circumference; and front thigh skinfolds. ANOVA with repeated measures was used to determine the interactions between training, locations of measurement, and legs, by groups. Post-hoc analysis with Bonferroni adjustment was used to determine the differences between mean values. Pearson product-moment correlation coefficient was used to evaluate the correlations between the measured variables.
Results indicated that the six weeks of training caused significant increases in MVC of the right leg in VG and E-VG (both p<0.01), while the E-VG also demonstrated a strength gain in the unexercised left leg (p<0.01). The CG showed no significant change in MVC (p>0.05). The strength gain was accompanied by a significant increase in CSA-quadriceps (p<0.01) measured at all three locations in the exercised leg, but no significant change was found in the unexercised leg. The CSA-thigh did not change significantly whilst the CSA-fat decreased at the upper and lower levels (p<0.05). Moderate correlation was found between improvement of MVC and variations of CSA-quadriceps measured at mid-thigh level (r=0.46, p<0.05) in the right leg, but not in the left leg. Moderate correlations were also found between variations in MVC and thigh circumference of the right leg measured at upper (r=0.52, p<0.01) and mid-thigh (r=0.44, p<0.05) levels, but not in the left leg. Skinfolds demonstrated significant and moderate correlations to the CSA-fat (r=0.83-0.93, p<0.01) and thigh circumference (r=0.72-0.87, p<0.01). The variations of skinfolds measured showed better correlations to CSA-fat at mid thigh levels (r=0.39-0.52, p<0.05) than that at upper and lower levels (mostly p>0.05).
Discussion and conclusion
The major findings in this study included that:
1) the six weeks of VC and E-VC training significantly improved muscular strength of the trained limb, while the E-VC also caused strength gain in the contralateral limb that further confirmed the effectiveness of electrical stimulation in inducing cross education;
2) the strength gain observed in the trained limb could be partially explained by muscle hypertrophy as indicated by increased CSA of the quadriceps;
3) the strength gain observed in the unexercised contralateral limb was not correlated to muscle CSA changes, therefore would be mainly due to neural adaptations;
4) MRI analysis of muscle and fat CSA provided more accurate assessments for muscle hypertrophy in response to training, and the images taken at the three locations demonstrated similar trend of changes;
5) the thigh circumferences taken at the upper and mid thigh levels demonstrated moderate correlations to strength variation; and
6) skinfolds taken at the selected locations demonstrated significant correlations to CSA of fat and thigh circumference, particularly at mid thigh level, however were not correlated to the strength gain.
The information obtained in this study would be useful in selection of valid measurements for neuromuscular adaptations to resistance training in future investigations.