Biomedical subjects

Nathan K LeBrasseur

Publications and source records attributed to Nathan K LeBrasseur.

3 recordsLinked to original sources

PubMed2003

Differential activation of mTOR signaling by contractile activity in skeletal muscle.

The cellular mechanisms by which contractile activity stimulates skeletal muscle hypertrophy are beginning to be elucidated and appear to include activation of the phosphatidylinositol 3-kinase signaling substrate mammalian target of rapamycin (mTOR). We examined the time course and location of mTOR phosphorylation in response to an acute bout of contractile activity. Rat hindlimb muscle contractile activity was elicited by high-frequency electrical stimulation (HFES) of the sciatic nerve. Plantaris (Pla), tibialis anterior (TA), and soleus (Sol) muscles from stimulated and control limbs were collected immediately or 6 h after stimulation. HFES resulted in mTOR phosphorylation immediately after (3.4 +/- 0.9-fold, P < 0.01) contractile activity in Pla, whereas TA was unchanged compared with controls. mTOR phosphorylation remained elevated in Pla (3.6 +/- 0.6-fold) and increased in TA (4.6 +/- 0.9-fold, P < 0.05) 6 h after HFES. Interestingly, mTOR activation occurred predominantly in fibers expressing type IIa but not type I myosin heavy chain isoform. Furthermore, HFES induced modest ribosomal protein S6 kinase phosphorylation immediately after exercise in Pla (0.4 +/- 0.1-fold, P < 0.05) but not TA and more markedly 6 h after in both Pla and TA (1.4 +/- 0.4-fold vs. 2.4 +/- 0.3-fold, respectively, P < 0.01). Akt/PKB phosphorylation was similar to controls at both time points. These results suggest that mTOR signaling is increased after a single bout of muscle contractile activity. Despite reports that mTOR is activated downstream of Akt/PKB, in this study, HFES induced mTOR signaling independent of Akt/PKB phosphorylation. Fiber type-dependent mTOR phosphorylation may be a molecular basis by which some fiber types are more susceptible to contraction-induced hypertrophy.

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PubMed2003

Changes in function and disability after resistance training: does velocity matter?: a pilot study.

OBJECTIVE: To compare the effects of high- and low-velocity resistance training on functional performance and disability outcomes in physically limited older women. DESIGN: A total of 16 wk of high-velocity resistance training or traditional low-velocity resistance training consisting of knee extension and leg press exercises was performed three times per week by 30 women with self-reported disability to compare their effect on functional performance and disability. Tests of dynamic balance, stair-climb time, chair-rise time, and gait velocity were used to assess changes in functional performance. Changes in disability were assessed using the Medical Outcomes Study Short Form. RESULTS: Dynamic balance and stair-climb time improved 8% and 10%, respectively, with training. Self-reported disability, physical functioning, role physical, and mental health improved 11, 9, and 5% with training, respectively. There were no significant differences between high- and low-velocity training groups. CONCLUSIONS: High- and low-velocity training achieved similar improvements in functional performance and disability. Improvements in functional performance and disability were modest compared with robust increases in strength and power. Specific modes of training or behavioral strategies may be necessary to optimize improvements in these outcomes.

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PubMed2002

High-velocity resistance training increases skeletal muscle peak power in older women.

OBJECTIVES: Peak power declines more precipitously than strength with advancing age and is a reliable measure of impairment and a strong predictor of functional performance. We tested the hypothesis that a high-velocity resistance-training program (HI) would increase muscle power more than a traditional low-velocity resistance-training program (LO). DESIGN: Randomized controlled trial. SETTING: University-based human physiology laboratory. PARTICIPANTS: Thirty women with self-reported dis-ability (aged 73 + 1, body mass index 30.1 + 1.1 kg/mn). INTERVENTION: We conducted a randomized trial comparing changes in skeletal muscle power and strength after 16 weeks of HI or LO. Training was performed three times per week, and subjects completed three sets (8-10 repetitions) of leg press (LP) and knee extension (KE) exercises at 70% of the one-repetition maximum (IRM). MEASUREMENTS: One-repetition maximum (1 RM) and peak power for KE and LP. RESULTS: LP and KE relative training force and total work were similar between groups (P > .05). However, HI generated significantly higher power during training sessions than LO for LP (3.7-fold greater, P < .001) and KE (2.1-fold greater, P < .001). Although LP and KE 1RM muscle strength increased similarly in both groups asa result of the training (P < .001), LP peak power increased significantly more in HI than in LO (267 W vs 139 W, P < .001). Furthermore, HI resulted in a significantly greater improvement in LP power at 40%, 50%, 60%,70%, 80%, and 90% of the 1 RM than did LO (P <.05). CONCLUSIONS: HI improved 1RM strength similarly and was more effective in improving peak power than was traditional LO in older women. Improvements in lower extremity peak power may exert a greater influence on age-associated reductions in physical functioning than other exercise interventions.

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