Influence of Intensive Cycling Training on Heart Rate Variability During Rest and Exercise

The current study examined whether changes in heart rate variability (HRV) following intensive cycling training contribute to the mechanism of training-induced bradycardia. Thirteen healthy untrained subjects, ages 18-27 years, underwent recordings of heart rate (HR) and [Formula: see text] before and after 8 weeks of cycling, 25-60 min/day, 5 days/week at > 80% maximum HR (HRmax). Heart rate recordings were obtained during supine rest and submaximal exercise and were analysed for the following components of HRV: low frequency (LF, 0.041-0.15 Hz); high frequency (HF, 0.15-0.40 Hz); LF/HF ratio and total power (TP, 0-0.40 Hz). At posttraining, VO2max was significantly increased while HR was significantly reduced at rest and all absolute exercise work rates. Training-induced lower HR was accompanied by significantly greater HF and TP during rest as well as LF, HF, and TP during all absolute exercise work rates. Posttraining HR and the majority of HRV measures were similar to pretraining values at the same relative exercise intensity (% HRmax). These results indicated that 8 weeks of intensive cycling training increased HRV and cardiac vagal modulation during rest and absolute exercise work rates but had little effect during relative exercise work rates. Increased vagal modulation resulting from intensive exercise training may contribute to the mechanism of training-induced bradycardia. Key words: exercise training, autonomic nervous system, bradycardia, vagal modulation

Glycogen Storage in Fetuses of Trained Pregnant Rats

The purpose was to determine if running 30 m/min on a 10° incline, 60 min/day for 5 days/week altered fetal glycogen storage in prepregnancy trained rats. Animals that exercised for 3 weeks prior to pregnancy either continued the same exercise program until Day 19 of gestation (pregnant running group [PR]), or ceased exercising at conception (pregnant controls [PC]). A separate set of animals did not exercise either before or during pregnancy (pregnant nonrunning control group [PNRC]). On Day 20 of gestation, fetal organs and placenta were weighed and analyzed for glycogen concentration. Glycogen concentrations were not different in either fetal liver, heart, or placenta of PR rats compared to PNRC animals. However, fetal liver glycogen concentration was significantly lower in the fetal heart and liver of PC animals compared to glycogen measured in both PNRC and PR animals (p < .0.5). These results suggest that exercise of this intensity does not compromise fetal glycogen storage in trained pregnant rats. However, chronic prepregnancy exercise and then abrupt cessation of exercise at conception may compromise fetal growth and development. Key words: exercise training, pregnancy, fetal glycogen

Is Increased Voluntary Motor Activity Beneficial or Detrimental During the Period of Motor Nerve Regeneration/Reinnervation?

A model of partial denervation of the rat lateral gastrocnemius was used to investigate the effects of daily activity (treadmill plus voluntary wheel exercise) on the regeneration/reinnervation of motoneurons recovering from nerve crush. It appears that increased activity has no effect on axon regeneration rate, but may be detrimental to the reinnervation process. Key words: exercise, training, denervation, motoneuron, axotomie