Prolonged cycling lowers subsequent running mechanical efficiency in collegiate triathletes

Background

A significant challenge that non-elite collegiate triathletes encounter during competition is the decline in running performance immediately after cycling. Therefore, the purpose of this study was to determine if performing a 40-km bout of cycling immediately before running would negatively influence running economy and mechanical efficiency of running during simulated race conditions in collegiate triathletes.

Methods

Eight competitive club-level collegiate triathletes randomly performed two trials: cycling for 40 km (Cycle-Run) or running for 5 km (Run–Run), immediately followed by a four-minute running economy and mechanical efficiency of running test at race pace on an instrumented treadmill. Blood lactate, respiratory exchange ratio, mechanical work, energy expenditure, and muscle glycogen were also measured during the four-minute running test.

Results

Mechanical efficiency of running, but not running economy, was significantly lower in Cycle-Run, compared to Run–Run (42.1 ± 2.5% vs. 48.1 ± 2.5%, respectively; p = 0.027). Anaerobic energy expenditure was significantly higher in the Cycle-Run trial, compared to the Run–Run trial (16.3 ± 2.4 vs. 7.6 ± 1.1 kJ; p = 0.004); while net (151.0 ± 12.3 vs. 136.6 ± 9.6 kJ; p = 0.204) and aerobic energy expenditure (134.7 ± 12.3 vs. 129.1 ± 10.5 kJ; p = 0.549) were not statistically different between trials. Analysis of blood lactate, respiratory exchange ratio, mechanical work, and changes in muscle glycogen revealed no statistically significant differences between trials.

Conclusions

These results suggest that mechanical efficiency of running, but not running economy, is decreased and anaerobic energy expenditure is increased when a 40-km bout of cycling is performed immediately before running in collegiate triathletes.

Ajuga turkestanica increases Notch and Wnt signaling in aged skeletal muscle

BACKGROUND

The declining myogenic potential of aged skeletal muscle is multifactorial. Insufficient satellite cell activity is one factor in this process. Notch and Wnt signaling are involved in various biological processes including orchestrating satellite cell activity within skeletal muscle. These pathways become dysfunctional during the aging process and may contribute to the poor skeletal muscle competency. Phytoecdysteroids are natural adaptogenic compounds with demonstrated benefit on skeletal muscle.

AIM

To determine the extent to which a phytoecdysteroid enriched extract from Ajuga turkestanica (ATE) affects Notch and Wnt signaling in aged skeletal muscle.

MATERIALS AND METHODS

Male C57BL/6 mice (20 months) were randomly assigned to Control (CT) or ATE treatment groups. Chow was supplemented with either vehicle (CT) or ATE (50 mg/kg/day) for 28 days. Following supplementation, the triceps brachii muscles were harvested and immunohistochemical analyses performed. Components of Notch or Wnt signaling were co-labelled with Pax7, a quiescent satellite cell marker.

RESULTS

ATE supplementation significantly increased the percent of active Notch/Pax7+ nuclei (p = 0.005), Hes1/Pax7+ nuclei (p = 0.038), active B-catenin/Pax7+ nuclei (p = 0.011), and Lef1/Pax7+ nuclei (p = 0.022), compared to CT. ATE supplementation did not change the resting satellite cell number.

CONCLUSIONS

ATE supplementation in aged mice increases Notch and Wnt signaling in triceps brachii muscle. If Notch and Wnt benefit skeletal muscle, then phytoecdysteroids may provide a protective effect and maintain the integrity of aged skeletal muscle.

Non-passaged muscle precursor cells from 32-month old rat skeletal muscle have delayed proliferation and differentiation

OBJECTIVES

The systemic environment and satellite cell dysfunction have been proposed as important contributors in the development of sarcopenia and impaired skeletal muscle regrowth with ageing. In the present study, we investigated effects of serum age on proliferation of muscle precursor cells (MPCs) isolated from skeletal muscles of young and old rats.

MATERIALS AND METHODS

We examined proliferation and subsequent differentiation of non-passaged MPCs isolated from skeletal muscles of 1-, 3- and 32-month old rats over a 72-h time course, using a serum cross-over design.

RESULTS AND CONCLUSIONS

We found no effect of serum age on MPC proliferation, but we did discover that MPCs isolated from skeletal muscle of 32-month old rats had delayed onset of, and exit from proliferation, compared to MPCs isolated from skeletal muscle of 1-month old rats. Delayed proliferation of MPCs from 32-month old rats was associated with delayed p38 MAPK phosphorylation, and MyoD and p21(Cip1) protein expression. We also demonstrate that MPCs from 32-month old rats exhibited lower levels of muscle creatine kinase mRNA compared to 1-month old rats, but elevated levels of myogenin mRNA, when stimulated to differentiate after 36 h proliferation. These findings suggest that delayed entry and exit of the cell cycle observed in MPCs from 32-month old rats may compromise their ability to respond to differentiation stimuli and subsequently impair myogenic potential of 32-month old skeletal muscle, in this model.

Basic concepts about genes, inactivity and aging

Remarkably, 80-year-old humans who have partaken in lifelong aerobic or strength training have maximal aerobic capacities or muscle strengths comparable with that of sedentary individuals aged 50 or 55-year-old, respectively. Such delays in functional aging are clinically significant because lower aerobic and lower strength capacities increase the risk of premature death. In this short review, we speculate that the lack of daily physical activity induces evolutionarily selected mechanisms to use or lose, one of which is related to nutritional status.

Soleus, plantaris and gastrocnemius VEGF mRNA responses to hypoxia and exercise are preserved in aged compared with young female C57BL/6 mice

AIMS

In humans, skeletal muscle capillarization and the vascular endothelial growth factor (VEGF) mRNA response to acute exercise are lower in aged compared with young. The exercise-induced increase in VEGF mRNA has been proposed to involve hypoxic regulation of VEGF and is believed to be fibre type-dependent. We hypothesized that attenuated VEGF mRNA responses to hypoxia and exercise with advanced age would be greatest in oxidative vs. glycolytic muscles.

METHODS

3- and 24-month-old female C57BL/6 mice were exposed to acute hypoxia (FI O2 = 0.06) or performed a single exercise (65% of maximum treadmill running speed) bout. Capillarization and VEGF mRNA were analysed in the soleus, plantaris and gastrocnemius muscles.

RESULTS

In each muscle, VEGF mRNA was greater in aged compared with young, while the VEGF mRNA response to acute hypoxia or acute exercise was similar between young and aged. Morphological analysis revealed that type IIA fibre percentage and type IIB capillarization in the plantaris were greater and type IIB fibre cross-sectional area (FCSA) in the gastrocnemius was smaller in aged compared with young.

CONCLUSIONS

These findings suggest that ageing does not impair the potential for non-pathological angiogenesis in mice and that acute exercise increases VEGF mRNA in the soleus, plantaris and gastrocnemius muscles, which differ considerably in fibre type percentage.