Progressive resistance-loaded voluntary wheel running increases hypertrophy and differentially affects muscle protein synthesis, ribosome biogenesis, and proteolytic markers in rat muscle.

We examined if 6 weeks of progressive resistance-loaded voluntary wheel running in rats induced plantaris, soleus, and/or gastrocnemius hypertrophy and/or affected markers of translational efficiency, ribosome biogenesis, and markers of proteolysis. For 6 weeks, 8 male Sprague-Dawley rats (~9-10 weeks of age, ~300-325 g) rats were assigned to the progressive resistance-loaded voluntary wheel running model (EX), and ten rats were not trained (SED). For EX rats, the wheel-loading paradigm was as follows - days 1-7: free-wheel resistance, days 8-15: wheel resistance set to 20%-25% body mass, days 16-24: 40% body mass, days 25-32: 60% body mass, days 33-42: 40% body mass. Following the intervention, muscles were analysed for markers of translational efficiency, ribosome biogenesis, and muscle proteolysis. Raw gastrocnemius mass (+13%, p < .01), relative (body mass-corrected) gastrocnemius mass (+16%, p < .001), raw plantaris mass (+13%, p < .05), and relative plantaris mass (+15%, p < .01) were greater in EX vs. SED rats. In spite of gastrocnemius hypertrophy, EX animals presented a 54% decrease in basal muscle protein synthesis levels (p < .01), a 125% increase in pan 4EBP1 levels (p < .001) and a 31% decrease in pan eIF4E levels (p < .05). However, in relation to SED animals, EX animals presented a 70% increase in gastrocnemius c-Myc protein levels (p < .05). Most markers of translational efficiency and ribosome biogenesis were not altered in the plantaris or soleus muscles of EX vs. SED animals. Gastrocnemius F-box protein 32 and poly-ubiquinated protein levels were approximately 150% and 200% greater in SED vs. EX rats (p < .001). These data suggest that the employed resistance training model increases hind limb muscle hypertrophy, and this may be mainly facilitated through reductions in skeletal muscle proteolysis, rather than alterations in ribosome biogenesis or translational efficiency.

High-intensity interval training has positive effects on performance in ice hockey players.

In spite of the well-known benefits that have been shown, few studies have looked at the practical applications of high-intensity interval training (HIIT) on athletic performance. This study investigated the effects of a HIIT program compared to traditional continuous endurance exercise training. 24 hockey players were randomly assigned to either a continuous or high-intensity interval group during a 4-week training program. The interval group (IG) was involved in a periodized HIIT program. The continuous group (CG) performed moderate intensity cycling for 45-60 min at an intensity that was 65% of their calculated heart rate reserve. Body composition, muscle thickness, anaerobic power, and on-ice measures were assessed pre- and post-training. Muscle thickness was significantly greater in IG (p=0.01) when compared to CG. The IG had greater values for both ∆ peak power (p<0.003) and ∆ mean power (p<0.02). Additionally, IG demonstrated a faster ∆ sprint (p<0.02) and a trend (p=0.08) for faster ∆ endurance test time to completion for IG. These results indicate that hockey players may utilize short-term HIIT to elicit positive effects in muscle thickness, power and on-ice performance.

ß2 Adrenoceptor signaling-induced muscle hypertrophy from blood flow restriction: is there evidence?

Skeletal muscle hypertrophy and increases in muscular function have been observed following low intensity/load exercise with blood flow restriction (BFR). The mechanisms behind these effects are largely unknown, but have been hypothesized to include a metabolic accumulation induced increase in muscle activation, elevations in growth hormone, and improvements in muscle protein balance. However, many of the aforementioned mechanisms are not present with BFR in the absence of exercise. In these situations, signaling through the ß2 adrenoceptor has been hypothesized to possibly contribute to the positive muscle adaptions, possibly in concert with muscle cell swelling. Signaling through the ß2 adrenoceptor has been shown to stimulate both muscle protein synthesis and an inhibition of protein degradation through increasing cyclic adenosine monophosphate (cAMP) or signaling via the Gßγ subunit, especially in situations where the basal rates of protein synthesis are already reduced. Every study that has investigated the catecholamine response to BFR in the absence of exercise or in combination with exercise has shown a significant increase above resting conditions. However, from the available evidence, it is unlikely that the norepinephrine response from BFR, particularly with exercise, is playing a prominent role with muscle adaptation in skeletal muscle that is not immobilized by a cast or joint injury.