Comparison between voluntary and stimulated contractions of the quadriceps femoris for growth hormone response and muscle damage

Abstract

NA.Comparison between voluntary and stimulated contractions of the quadriceps femoris for growth hormone response and muscle damage. J Appl Physiol 104: 75-81, 2008. First published November 1, 2007 doi:10.1152/japplphysiol.00335.2007.-This study aimed to compare voluntary and stimulated exercise for changes in muscle strength, growth hormone (GH), blood lactate, and markers of muscle damage. Nine healthy men had two leg press exercise bouts separated by 2 wk. In the first bout, the quadriceps muscles were stimulated by biphasic rectangular pulses (75 Hz, duration 400 s, on-off ratio 6.25-20 s) with current amplitude being consistently increased throughout 40 contractions at maximal tolerable level. In the second bout, 40 voluntary isometric contractions were performed at the same leg press force output as the first bout. Maximal voluntary isometric strength was measured before and after the bouts, and serum GH and blood lactate concentrations were measured before, during, and after exercise. Serum creatine kinase (CK) activity and muscle soreness were assessed before, immediately after, and 24, 48, and 72 h after exercise. Maximal voluntary strength decreased significantly (P Ͻ 0.05) after both bouts, but the magnitude of the decrease was significantly (P Ͻ 0.05) greater for the stimulated contractions (Ϫ22%) compared with the voluntary contractions (Ϫ9%). Increases in serum GH and lactate concentrations were significantly (P Ͻ 0.05) larger after the stimulation compared with the voluntary exercise. Increases in serum CK activity and muscle soreness were also significantly (P Ͻ 0.05) greater for the stimulation than voluntary exercise. It was concluded that a single bout of electrical stimulation exercise resulted in greater GH response and muscle damage than voluntary exercise. neuromuscular electrical stimulation; isometric strength; blood lactate; creatine kinase; muscle soreness IN RECENT YEARS, THE ACUTE effects of neuromuscular electrical stimulation (NMES) on neuromuscular and metabolic responses have received attention (16,28,33,37,39). It has been reported in several studies that electrically evoked contractions result in greater strength loss and greater increases in oxygen consumption and blood lactate compared with voluntary contractions at the same intensity (16,28,33,37,39). It has been speculated that the specific recruitment pattern of motor units during NMES is mainly attributed to the phenomena (16,28,37,39). Indeed, it is documented that the recruitment of motor units during stimulated contractions is different from voluntary contraction such that fast-twitch fibers could be activated at relatively low force levels (i.e., random/nonselective motor unit recruitment) (10,17,20,30).It is known that acute voluntary resistance exercise increases growth hormone (GH) secretion (for review see 22); however, limited information is available for acute GH responses to NMES. To the best of our knowledge, only two studies have reported GH responses to NMES. Greisen et al. (11) showed a significant increa...

GH responses to two consecutive bouts of neuromuscular electrical stimulation in healthy adults

“…The present study confirms that NMES administered at the same frequency (75 Hz) and intensity (w26% MVC force), but for a shorter period (9 min versus 18 min) than in our previous study (13), is able to induce significant GH responses. These results indicate that GH responsiveness to NMES is strictly dependent on the duration of the stimulus.…”

“…We have recently demonstrated that a single bout of NMES exercise is able to induce markedly higher GH responses than those obtained with voluntary contractions of the same intensity (13). This finding is probably related to the higher degree of muscle fatigue, higher blood lactate concentration and pain induced by electrical muscle stimulation.…”

“…In the last few years, NMES has been used in rehabilitation, geriatric and sport medicine (for review, (9, 10)), with the general objectives to a) minimize the effects of prolonged immobilization or disuse on skeletal muscle structure and function and b) improve neuromuscular function parameters in healthy individuals. More recently, the acute effects of NMES on neuromuscular, metabolic and hormonal responses have also received attention (11)(12)(13). We have demonstrated that a single bout of NMES exercise is able to show GH responsiveness in healthy subjects (13).…”

“…The quadriceps femoris muscles of both legs were exercised simultaneously using standard surface NMES techniques (13). Two bouts of 20 isometric NMES contractions (9-min duration) were administered separated by a 2-h interval.…”

“…More recently, the acute effects of NMES on neuromuscular, metabolic and hormonal responses have also received attention (11)(12)(13). We have demonstrated that a single bout of NMES exercise is able to show GH responsiveness in healthy subjects (13). However, GH response after a series of 40 stimulated contractions was lower than that observed after pharmacological and/or voluntary exercise stimuli (4,8).…”