Acta physiol. scand. 1976. 98. 232-236 From the Department of Physiology, Gymnastik- och idrottshogskolan, Stockholm, Sweden, and the Kinesiology Laboratory, University of Jyvaskyla, Finland
Effect of Strength Training on EMG of Human Skeletal Muscle BY
A. THORSTENSSON, J. KARLSSON, J. H. T. VIITASALO, P. LUHTANEN and P. V. KOMI Received 17 March 1976
Abstract THORSTENSSON, A., J. KARLSSON, J. H. T. VIITASALO, P. LUHTANEN and P. V. KOMI.Effect of strength training OIZ EMG of human skeletal muscle. Acta physiol. scand. 1976. 98. 232-236. The effects of an 8 weeks period of systematic progressive strength training on the EMG activity of the leg extensor muscles (vastus lateralis and rectus fernoris) were investigated in 8 healthy male subjects (2231 yrs). After training there were indications (n.s.) of a decline in integrated E M G (IEMG) during maximal isometric knee extension a s well as in the IEMG vs isometric force relationship. The averaged motor unit potential (AMUP) did not demonstrate any significant changes due to the strength training regimen. In conformity with earlier findings no or only minor alterations were observed i n anthropometrics, muscle enzyme activities and fibre composition. The fibre area ratio indicated a specific effect of the training stimuli on the fast twitch muscle fibres. Thus, EMG-analyses, as employed in the present study, did not provide any conclusive additional explanation as to the mechanisms behind the well established gains in niuscle strength performance induced by the applied strength training program.
Improvement of muscular strength with training may occur in several components of the muscle function, e.g. muscle fibre composition, enzymatic activity, innervation pattern, and elastic component. In our previous study of 8 weeks of systematic progressive strength training, marked improvements in muscular strength were accompanied by slight changes in body composition but no or only minor alterations in e.g. fibre characteristics and enzyme activities (Thorstensson et al. 1976). The present investigation was undertaken to extend our study to deal also with electrical parameters involved in the neuromuscular function by including various EMG analyses in the testing schedule.
Material and methods 8 healthy male students of physical education, with no previous experience of systematic strength training, participated in the study. The mean age, height, and weight (before training) (fS. E. ) were 2 4 2 1 yrs, 1801- 2 cm and 76.9 3.0 kg, respectively. The training program has been described earlier (Thorstensson et a[. 1976). Briefly, it consisted of 3
training sessions a week over an 8 weeks period. The subjects performed primarily squats,l but also vertical Squats= knee bending and extension with weights on the shoulders.
232
STRENGTH TRAINING ON EMG
233
TABLE 1. Results of the various tests applied before and after 8 weeks of strength training.
1 R M in squats, kg Vertical jump, cm Standing broad jump, cm Total leg force (90"), N Total leg force (73"), N Quadriceps force, N Max. I EM G rectus femoris, pV Max I E M G vastus lateralis, pV Body weight, kg Thigh girth, c m Calf girth, cm Lean body mass, kg Total body K+, g Muscle mass, kg FT, FT/ST area ratio Mg2+ stim. ATPasea M yo k I ]laseu Creatine phosphokinase' (lo
Before
After
116 5 4 57 i 2 238 & 5 1814 i 8 5 3 109 k 2 1 2 843 k 5 9 601.3260 6 628.3 i62.3 76.9 2.2 54.5k 1.1 38.0+_0.7 64.8 5 1.7 155.4 4. I 29.61 I .3 55 *4 1.20 k0.05 0.075 +O.OlZ 1.30 + O . l l 1.07 i O . 1 1
201 i 7 * * * 64 +1** 249 i2** 2 109 *70*** 4 0 9 0 +269*** 878 i 5 3 524.7138.0 539.9k53.5 77.8k3.2 55.4+ 1.1* 38.150.8 66.7 2 2.2 160.2k5.4 31.3j1.5 56 i 4 1.37 50.06* 0.084f 0.013 1.36 2 0 . 0 9 1.00 k 0 . 0 7
*
'Enzyme activities are expressed
in moles x 10W ,\ 9-l ,' min-'. Intraindividual differences were tested by the paired Student's t-test, * = p < O . O 5 , * * = p - ; O . O I , and ***=p
Effect of Strength Training on EMG of Human Skeletal Muscle BY
A. THORSTENSSON, J. KARLSSON, J. H. T. VIITASALO, P. LUHTANEN and P. V. KOMI Received 17 March 1976
Abstract THORSTENSSON, A., J. KARLSSON, J. H. T. VIITASALO, P. LUHTANEN and P. V. KOMI.Effect of strength training OIZ EMG of human skeletal muscle. Acta physiol. scand. 1976. 98. 232-236. The effects of an 8 weeks period of systematic progressive strength training on the EMG activity of the leg extensor muscles (vastus lateralis and rectus fernoris) were investigated in 8 healthy male subjects (2231 yrs). After training there were indications (n.s.) of a decline in integrated E M G (IEMG) during maximal isometric knee extension a s well as in the IEMG vs isometric force relationship. The averaged motor unit potential (AMUP) did not demonstrate any significant changes due to the strength training regimen. In conformity with earlier findings no or only minor alterations were observed i n anthropometrics, muscle enzyme activities and fibre composition. The fibre area ratio indicated a specific effect of the training stimuli on the fast twitch muscle fibres. Thus, EMG-analyses, as employed in the present study, did not provide any conclusive additional explanation as to the mechanisms behind the well established gains in niuscle strength performance induced by the applied strength training program.
Improvement of muscular strength with training may occur in several components of the muscle function, e.g. muscle fibre composition, enzymatic activity, innervation pattern, and elastic component. In our previous study of 8 weeks of systematic progressive strength training, marked improvements in muscular strength were accompanied by slight changes in body composition but no or only minor alterations in e.g. fibre characteristics and enzyme activities (Thorstensson et al. 1976). The present investigation was undertaken to extend our study to deal also with electrical parameters involved in the neuromuscular function by including various EMG analyses in the testing schedule.
Material and methods 8 healthy male students of physical education, with no previous experience of systematic strength training, participated in the study. The mean age, height, and weight (before training) (fS. E. ) were 2 4 2 1 yrs, 1801- 2 cm and 76.9 3.0 kg, respectively. The training program has been described earlier (Thorstensson et a[. 1976). Briefly, it consisted of 3
training sessions a week over an 8 weeks period. The subjects performed primarily squats,l but also vertical Squats= knee bending and extension with weights on the shoulders.
232
STRENGTH TRAINING ON EMG
233
TABLE 1. Results of the various tests applied before and after 8 weeks of strength training.
1 R M in squats, kg Vertical jump, cm Standing broad jump, cm Total leg force (90"), N Total leg force (73"), N Quadriceps force, N Max. I EM G rectus femoris, pV Max I E M G vastus lateralis, pV Body weight, kg Thigh girth, c m Calf girth, cm Lean body mass, kg Total body K+, g Muscle mass, kg FT, FT/ST area ratio Mg2+ stim. ATPasea M yo k I ]laseu Creatine phosphokinase' (lo
Before
After
116 5 4 57 i 2 238 & 5 1814 i 8 5 3 109 k 2 1 2 843 k 5 9 601.3260 6 628.3 i62.3 76.9 2.2 54.5k 1.1 38.0+_0.7 64.8 5 1.7 155.4 4. I 29.61 I .3 55 *4 1.20 k0.05 0.075 +O.OlZ 1.30 + O . l l 1.07 i O . 1 1
201 i 7 * * * 64 +1** 249 i2** 2 109 *70*** 4 0 9 0 +269*** 878 i 5 3 524.7138.0 539.9k53.5 77.8k3.2 55.4+ 1.1* 38.150.8 66.7 2 2.2 160.2k5.4 31.3j1.5 56 i 4 1.37 50.06* 0.084f 0.013 1.36 2 0 . 0 9 1.00 k 0 . 0 7
*
'Enzyme activities are expressed
in moles x 10W ,\ 9-l ,' min-'. Intraindividual differences were tested by the paired Student's t-test, * = p < O . O 5 , * * = p - ; O . O I , and ***=p
