Thirty-five healthy men were matched and randomly assigned to one of four training groups that performed high-intensity strength and endurance training (C; n = 9), upper body only high-intensity strength and endurance training (UC; n = 9), high-intensity endurance training (E; n = 8), or high-intensity strength training (ST; n = 9). The C and ST groups significantly increased one-repetition maximum strength for all exercises (P < 0.05). Only the C, UC, and E groups demonstrated significant increases in treadmill maximal oxygen consumption. The ST group showed significant increases in power output. Hormonal responses to treadmill exercise demonstrated a differential response to the different training programs, indicating that the underlying physiological milieu differed with the training program. Significant changes in muscle fiber areas were as follows: types I, IIa, and IIc increased in the ST group; types I and IIc decreased in the E group; type IIa increased in the C group; and there were no changes in the UC group. Significant shifts in percentage from type IIb to type IIa were observed in all training groups, with the greatest shift in the groups in which resistance trained the thigh musculature. This investigation indicates that the combination of strength and endurance training results in an attenuation of the performance improvements and physiological adaptations typical of single-mode training.

ripheral blood concentrations of testosterone in males FLECK. Hormonal and growth factor responses to heavy resist-(9, 13, 19, 29). Furthermore, it has been suggested that ance exercise protocols. J. Appl, Physiol. 69(4): 1442-1450, training may influence resting values of testosterone (14-1990.-To examine endogenous anabolic hormone and growth training m a i lun ingivale t estosterone (14-factor responses to various heavy resistance exercise protocols 16). Limited data also indicate that human growth hor-(HREPs), nine male subjects performed each of six randomly mone may increase in response to an acute bout of assigned HREPs, which consisted of identically ordered exer-resistance exercise (25, 29, 33). VanHelder et al. (33) cises carefully designed to control for load [5 vs. 10 repetitions have demonstrated that human growth hormone elevamaximum (RM)], rest period length (1 vs. 3 min), and total tions may be dependent on specific exercise characteriswork effects. Serum human growth hormone (hGH), testoster-tics such as the load utilized and frequency of lifting one (T), somatomedin-C (SM-C), glucose, and whole blood exercise. To our knowledge, no data exist regarding solactate (HLa) concentrations were determined preexercise, matomedin-C responses to heavy resistance exercise promidexercise (i.e., after 4 of 8 exercises), and at 0, 5, 15, 30, 60, tocols. The purpose of this investigation was to deter-90, and 120 min postexercise. All HREPs produced significant mine the impact of load, rest period length, and total (P < 0.05) temporal increases in serum T concentrations, min te ima toftload, rest p rod th andmtota although the magnitude and time point of occurrence above work on serum testosterone, human growth hormone, resting values varied across HREPs. No differences were ob-and somatomedin-C response patterns during and after served for T when integrated areas under the curve (AUCs) different heavy resistance exercise protocols. were compared. Although not all HREPs produced increases in serum hGH, the highest responses were observed consequent METHODS to the H10/1 exercise protocol (high total work, 1 min rest, 10-RM load) for both temporal and time integrated (AUC) reNine healthy male subjects gave informed written consponses. The pattern of SM-C increases varied among HREPs sent to participate in this investigation. The physical and did not consistently follow hGH changes. Whereas tem-characteristics of the subjects were the following: age, poral changes were observed, no integrated time (A T "-) differ-24.66 ± 4.27 (SD) yr; height, 178.41 ± 7.77 cm; body ences between exercise protocols occurred. These data indicate that the release patterns (temporal or time integrated) observed mass, 81.08 l 12.03 kg; maximal oxygen consumption, are complex functions of the type of HREPs utilized and the 54.17 ±4.63 ml.kg-min-; and body fat 1596+4.18%. physiological mechanisms involved with determining periph-All subjects had recreational experience with resistance era] circulatory concentrations (e.g., clearance ...

An 8-wk progressive resistance training program for the lower extremity was performed twice a week to investigate the time course for skeletal muscle adaptations in men and women. Maximal dynamic strength was tested biweekly. Muscle biopsies were extracted at the beginning and every 2 wk of the study from resistance-trained and from nontrained (control) subjects. The muscle samples were analyzed for fiber type composition, cross-sectional area, and myosin heavy chain content. In addition, fasting blood samples were measured for resting serum levels of testosterone, cortisol, and growth hormone. With the exception of the leg press for women (after 2 wk of training) and leg extension for men (after 6 wk of training), absolute and relative maximal dynamic strength was significantly increased after 4 wk of training for all three exercises (squat, leg press, and leg extension) in both sexes. Resistance training also caused a significant decrease in the percentage of type IIb fibers after 2 wk in women and 4 wk in men, an increase in the resting levels of serum testosterone after 4 wk in men, and a decrease in cortisol after 6 wk in men. No significant changes occurred over time for any of the other measured parameters for either sex. These data suggest that skeletal muscle adaptations that may contribute to strength gains of the lower extremity are similar for men and women during the early phase of resistance training and, with the exception of changes in the fast fiber type composition, that they occur gradually.

Effects of a 10-week progressive strength training program composed of a mixture of exercises for increasing muscle mass, maximal peak force, and explosive strength (rapid force production) were examined in 8 young (YM) (29+/-5 yrs) and 10 old (OM) (61+/-4 yrs) men. Electromyographic activity, maximal bilateral isometric peak force, and maximal rate of force development (RFD) of the knee extensors, muscle cross-sectional area (CSA) of the quadriceps femoris (QF), muscle fiber proportion, and fiber areas of types I, IIa, IIb, and IIab of the vastus lateralis were evaluated. Maximal and explosive strength values remained unaltered in both groups during a 3-week control period with no training preceding the strength training. After the 10-week training period, maximal isometric peak force increased from 1311+/-123 N by 15.6% (p <.05) in YM and from 976+/-168 N by 16.5% (p <.01) in OM. The pretraining RFD values of 4049+/-791 N*s(-1) in YM and 2526+/-1197 N*s(-1) in OM remained unaltered. Both groups showed significant increases (p < .05) in the averaged maximum IEMGs of the vastus muscles. The CSA of the QF increased from 90.3+/-7.9 cm2 in YM by 12.2% (p <.05) and from 74.7+/-7.8 cm2 in OM by 8.5% (p <.001). No changes occurred in the muscle fiber distribution of type I during the training, whereas the proportion of subtype IIab increased from 2% to 6% (p < .05) in YM and that of type IIb decreased in both YM from 25% to 16% (p < .01) and in OM from 15% to 6% (p < .05). The mean fiber area of type I increased after the 10-week training in YM (p < .001) and OM (p < .05) as well as that of type IIa in both YM (p < .01) and OM (p < .01). The individual percentage values for type I fibers were inversely correlated with the individual changes recorded during the training in the muscle CSA of the QF (r=-.56, p < .05). The present results suggest that both neural adaptations and the capacity of the skeletal muscle to undergo training-induced hypertrophy even in older people explain the gains observed in maximal force in older men, while rapid force production capacity recorded during the isometric knee extension action remained unaltered during the present mixed strength training program.

Transgenic mice lacking a functional myostatin (MSTN) gene demonstrate greater skeletal muscle mass resulting from muscle fiber hypertrophy and hyperplasia (McPherron, A. C., A. M. Lawler, and S.-J. Lee. Nature 387: 83–90, 1997). Therefore, we hypothesized that, in normal mice, MSTN may act as a negative regulator of muscle mass. Specifically, we hypothesized that the predominately slow (type I) soleus muscle, which demonstrates greater atrophy than the fast (type II) gastrocnemius-plantaris complex (Gast/PLT), would show more elevation in MSTN mRNA abundance during hindlimb unloading (HU). Surprisingly, MSTN mRNA was not detectable in weight-bearing or HU soleus muscle, which atrophied 42% by the 7th day of HU in female ICR mice. In contrast, MSTN mRNA was present in weight-bearing Gast/PLT muscle and was significantly elevated (67%) at 1 day but not at 3 or 7 days of HU. However, the Gast/PLT muscle had only atrophied 17% by the 7th day of HU. Because the soleus is composed only of type I and IIa fibers, whereas the Gast/PLT expresses type IId/x and IIb in addition to type I and IIa, it was necessary to perform a more careful analysis of the relationship between MSTN mRNA levels and myosin heavy-chain (MHC) isoform expression (as a marker of fiber type). A significant correlation ( r = 0.725, P < 0.0005) was noted between the percentage of MHC isoform IIb expression and MSTN mRNA abundance in several muscles of the mouse hindlimb. These results indicate that MSTN expression is not strongly associated with muscle atrophy induced by HU; however, it is strongly associated with MHC isoform IIb expression in normal muscle.