Skeletal muscle plasticity with marathon training in novice runners.

The purpose of this study was to investigate leg muscle adaptation in runners preparing for their first marathon. Soleus and vastus lateralis (VL) biopsies were obtained from six recreational runners (23 ± 1 years, 61 ± 3 kg) before (T1), after 13 weeks of run training (T2), and after 3 weeks of taper and marathon (T3). Single muscle fiber size, contractile function (strength, speed, and power) and oxidative enzyme activity [citrate synthase (CS)] were measured at all three time points, and fiber type distribution was determined before and after the 16-week intervention. Training increased VO(2max) ∼9% (P<0.05). All soleus parameters were unchanged. VL MHC I fiber diameter increased (+8%; P<0.05) from T1 to T2. VL MHC I V(o) (-12%), MHC I power (-22%) and MHC IIa power (-29%) were reduced from T1 to T2 (P<0.05). No changes in VL single fiber contractile properties were observed from T2 to T3. No change was observed in soleus CS activity, whereas VL CS activity increased 66% (P<0.05). Our observations indicate that modest marathon training elicits very specific skeletal muscle adaptations that likely support the ability to perform 42.2 km of continuous running - further strengthening the existing body of evidence for skeletal muscle specificity.

Effects of age and resistance exercise on skeletal muscle interstitial prostaglandin F(2alpha).

Prostaglandin (PG) F2alpha has been shown to contribute to the anabolic events in skeletal muscle. We measured the skeletal muscle interstitial concentration of PGF2alpha at rest and following a standard bout of resistance exercise in eight young (27+/-2 year) and eight old (75+/-4 year) men. Interstitial PGF2alpha concentration was determined from microdialysate samples obtained from two microdialysis probes placed in the vastus lateralis. Microdialysates were collected 1h pre- and 5-6, 8-9, and 24-25 h postexercise. The exercise bout consisted of 4 exercises (3 sets of 8 replications at 80% 1 RM per exercise) emphasizing the quadriceps. Interstitial PGF2alpha levels were not different (P>0.05) between young and old at rest (1.50+/-0.35 vs. 1.52+/-0.30 ng ml-1) or at any time point following the resistance exercise bout. For the young and old combined there was a change (P<0.05) in PGF2alpha levels at 5-6 h (93%) and 8-9 h (95%), which had returned to preexercise levels by 24-25 h. These results show that PGF2alpha is increased in skeletal muscle following a standard bout of resistance exercise and aging does not alter interstitial levels of this PG at rest or after exercise. These data, coupled with previous findings, suggest that the anabolic factor PGF2alpha should be considered when discussing the complex processes that regulate muscle mass in young and old individuals.

Effects of short-term concentric vs. eccentric resistance training on single muscle fiber MHC distribution in humans.

The purpose of this investigation was to determine the effects of a concentric vs. eccentric resistance training program on single muscle fiber myosin heavy chain (MHC) adaptations in humans. Fifteen sedentary, healthy males were divided into three groups: concentric training (CTG) (n = 6, 24.2 +/- 1.7 y, 181 +/- 2 cm, 82.5 +/- 4.6 kg), eccentric training (ETG) (n = 6, 23.7 +/- 1.6 y, 178 +/- 3 cm, 90.4 +/- 6.1 kg), and control (CTL) (n = 3, 23 +/- 1.5 y, 181 +/- 2 cm, 97 +/- 13.2 kg). The subjects performed 4 sets of 8 unilateral repetitions starting at 80 % of concentric 1-RM, 3 days/week for a total of 4 weeks. Subjects were tested pre- and post-training for concentric 1-RM. Muscle biopsies were obtained from the vastus lateralis pre- and post-training for determination of single fiber MHC isoform distribution using SDS-PAGE/silver staining (100 fibers analyzed/subject pre- and post-training). Fibers expressing more than one MHC isoform (i.e., hybrid fibers) were analyzed for relative MHC isoform proportions via densitometry. The training program resulted in a 19 % 1-RM strength gain for CTG (p < 0.05) with no change in ETG or CTL. MHC-IIx fibers decreased by 7 % in CTG (p < 0.05) and ETG had an 11 % increase in total hybrids (MHC-I/IIa + MHC-IIa/IIx) (p < 0.05). No other differences were noted in MHC distribution among the three groups. Densitometry analysis of hybrid fibers showed no change in relative MHC isoform proportions pre- to post-training for any group. These data suggest that the MHC distribution did not change dramatically as a result of 4 weeks of concentric vs. eccentric resistance training despite the increase in whole muscle strength from concentric muscle actions.

Human soleus muscle protein synthesis following resistance exercise.

AIM: It is generally believed the calf muscles in humans are relatively unresponsive to resistance training when compared with other muscles of the body. The purpose of this investigation was to determine the muscle protein synthesis response of the soleus muscle following a standard high intensity bout of resistance exercise. METHODS: Eight recreationally active males (27 +/- 4 years) completed three unilateral calf muscle exercises: standing calf press/heel raise, bent-knee calf press/heel raise, and seated calf press/heel raise. Each exercise consisted of four sets of 15 repetitions (approximately 15 repetition maximum, RM, or approximately 70% 1RM). Fractional rate of muscle protein synthesis (FSR) was determined with a primed constant infusion of [2H5]phenylalanine coupled with muscle biopsies immediately and 3 h following the exercise in both the exercise and non-exercise (resting control) leg. RESULTS: FSR was elevated (P < 0.05) in the exercise (0.069 +/- 0.010) vs. the control (0.051 +/- 0.012) leg. Muscle glycogen concentration was lower (P < 0.05) in the exercise compared with the control leg (Decrease from control; immediate post-exercise: 54 +/- 5; 3 h post-exercise: 36 +/- 4 mmol kg(-1) wet wt.). This relatively high amount of glycogen use is comparable with previous studies of resistance exercise of the thigh (i.e. vastus lateralis; approximately 41-49 mmol kg(-1) wet wt.). However, the exercise-induced increase in FSR that has been consistently reported for the vastus lateralis (approximately 0.045-0.060% h(-1)) is on average approximately 200% higher than reported here for the soleus (0.019 +/- 0.003% h(-1)). CONCLUSIONS: These results suggest the relatively poor response of soleus muscle protein synthesis to an acute bout of resistance exercise may be the basis for the relative inability of the calf muscles to respond to resistance training programs.

Alterations in single muscle fiber calcium sensitivity with resistance training in older women.

The purpose of this investigation was to determine the effects of a 12-week progressive resistance-training program (PRT) on single muscle fiber calcium sensitivity in six older women (73 +/- 2 years). Muscle biopsy samples of the vastus lateralis were obtained pre- and post-PRT. Chemically skinned single muscle fibers ( n=274) were dissected and studied. The experimental sequence for each fiber was the determination of peak maximal isometric tension ( P(o)) at pCa 4.5 (pCa=-log[Ca(2+)]), and then subsequent submaximal activations of the fiber at nine Ca(2+) concentrations (pCa 6.8 to 4.7). Myosin heavy chain (MHC) I fiber (slow-twitch) diameter increased 16% ( P<0.05) with no change in MHC IIa fibers (fast-twitch) pre- to post-PRT, respectively. P(o) in MHC I fibers increased 34% ( P<0.05) as a result of the training with no change in MHC IIa fibers. The mean MHC I Ca(2+) activation threshold (minimal amount of Ca(2+) necessary to induce tension) increased from 6.83 +/- 0.02 to 6.91 +/- 0.01 ( P<0.05), as did the mean half-maximal activation (pCa(50)), 5.51 +/- 0.02 to 5.71 +/- 0.03 ( P<0.05) with PRT. The slope of the Hill plot above ( n(1)) the pCa(50) for MHC I did not change significantly with the PRT. However, the slope of the Hill plot below ( n(2)) the pCa(50) for MHC I demonstrated an increase ( P<0.05) with training. There were no differences with MHC IIa fibers with PRT for any of the variables measured. In conclusion, the results of this investigation indicate that myofibril Ca(2+) sensitivity and activation properties are altered in MHC I, but not MHC IIa fibers with PRT in older women. The alterations in the MHC I Ca(2+) properties appear to have an effect on the mechanisms involved with skeletal muscle adaptability in older women following PRT.

Reduction in hybrid single muscle fiber proportions with resistance training in humans.

The purpose of this investigation was to examine the effects of 12 wk of progressive resistance training (PRT) on single muscle fiber myosin heavy chain (MHC; I, I/IIa, I/IIa/IIx, IIa, IIa/IIx, IIx) isoform proportions in young individuals. Young, untrained men (YM; n = 6) and women (YW; n = 6) (age = 22 +/- 1 and 25 +/- 2 yr for YW and YM, respectively) received pre- and post-PRT muscle biopsies from the right vastus lateralis for single muscle fiber MHC distribution by electrophoretic analysis (192 +/- 5 pre- and 183 +/- 6 post-fibers/subject analyzed; 4,495 fibers total). Data are presented as percentages of the total fibers analyzed per subject. The PRT protocol elicited an increase in the pure MHC IIa (Delta = + 24 and + 27; YW and YM, respectively; P < 0.05) with no change in the pure MHC I distribution. The hybrid MHC distributions decreased I/IIa/IIx (Delta = -2; YM and YW; P < 0.05), IIa/IIx (Delta = -13 and -19 for YM and YW, respectively; P < 0.05), and total hybrid fiber proportion (I/IIa + I/IIa/IIx + IIa/IIx) decreased (Delta = -19 and -30 for YM and YW, respectively; P < 0.05) with the training, as did the MHC IIx distribution (Delta = -2; YW only; P < 0.05). Alterations in the predominance of MHC isoforms within hybrid fibers (decrease in MHC I-dominant I/IIa and nondominant MHC IIa/IIx, increase in MHC IIa-dominant IIa/IIx; P < 0.05) appeared to contribute to the increase in the MHC IIa proportion. Electrophoresis of muscle cross sections revealed an approximately 7% increase (P < 0.05) in MHC IIa proportion in both groups, whereas the MHC IIx decrease by 7.5 and 11.6% post-PRT in YW and YM, respectively. MHC I proportions increase in YM by 4.8% (P < 0.05) post-PRT. These findings further support previous resistance training data in young adults with respect to the increase in the MHC IIa proportions but demonstrate that a majority of the change can be attributed to the decrease in single-fiber hybrid proportions.