Growth hormone and muscle function responses to skeletal muscle ischemia.
We examined the effects of ischemia (ISC) alone and with low-intensity exercise (ISC+EX) on growth hormone (GH) and muscle function responses. Nine men (22 +/- 0.7 yr) completed 3 study days: an ISC day (thigh cuff inflated five times, 5 min on, 3 min off), an ISC+EX day [knee extension at 20% maximal voluntary contraction (MVC) with ISC], and a control day. MVCs and submaximal contraction tasks (15 and 30% MVC) were performed before and following the perturbations. Surface electromyogram signals were collected from thigh muscles and analyzed for median frequency and root mean square alterations. Blood samples were collected every 10 min (190 min total) and analyzed for GH concentrations. Peak GH concentrations and GH area under the curve were highest (P < 0.01) on the ISC+EX day (7.5 microg/l and 432 microg.l(-1).min(-1), respectively) compared with the ISC (0.9 microg/l and 76.4 microg.l(-1).min(-1)), and CON (1.1 microg/l and 83.8 microg.l(-1).min(-1)) days. A greater GH pulse amplitude, mass/pulse, and production rate were also observed on the ISC+EX day (P < 0.05). Following the intervention, force production decreased on the ISC and ISC+EX days by 16.1 and 55.8%, respectively, and did not return to baseline values within 5 min of recovery. During the submaximal contractions, median frequency shifted to lower frequencies for most of the muscles examined, and root mean square electromyogram was consistently elevated for ISC+EX day. In conclusion, ISC coupled with resistance exercise acutely increases GH levels and reduces MVC, whereas ISC alone decreases force capacity, without alterations in GH levels.
Pierce
Joseph R
JR
Department of Exercise Science, Syracuse University, Syracuse, New York, USA.
Clark
Brian C
BC
Ploutz-Snyder
Lori L
LL
Kanaley
Jill A
JA
D000222:Adaptation, Physiological; D000328:Adult; D013006:Growth Hormone / Q000097:blood*; D006801:Humans; D007511:Ischemia / Q000503:physiopathology*; D007537:Isometric Contraction; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000503:physiopathology*; D010807:Physical Endurance; D005082:Physical Exertion
D013006:Growth Hormone