EFFECTS OF FOLLICULAR PHASE EXERCISE ON LUTEINIZING-HORMONE PULSE CHARACTERISTICS IN SEDENTARY EUMENORRHEIC WOMEN

OBJECTIVE Current studies reveal little regarding the inception of exe rcise-induced LH changes during physical training. This study aimed to assess the susceptibility of the hypothalamic-pituitary axis to the a cute physical stress of exercise in untrained, physically inactive wom en. The acute effects of submaximal endurance exercise upon the pulsat ile LH secretion in the follicular phase were compared with those acco mpanying leisurely strolling for a similar time period. SUBJECTS All s ubjects were eumenorrhoeic, as determined by biphasic temperature patt erns, detection of the urinary LH surge, and mid-luteal serum progeste rone levels. Subjects were not physically active and had little histor y of strenuous exercise (VO(2)max = 38.0 +/- 1.8) (mean +/- SEM) ml/kg /min). DESIGN All women completed a 13.5-hour pulsatility test which i ncluded three consecutive 20-minute runs on a treadmill at 50, 60 and 70% of the subjects' maximum oxygen uptake (n=16). Six of these same s ubjects completed a separate test on another occasion in which one hou r of leisurely strolling was substituted for exercise. Blood was sampl ed every 10 minutes via an indwelling cannula for 4.5 hours before and 8 hours after one hour of exercise and or strolling. MEASUREMENTS A p ulse algorithm (Pulsar) was used to quantify LH pulse characteristics. RESULTS Exercise produced no significant effects upon LH pulse freque ncy or mean serum LH concentration. However, exercise of moderate inte nsity caused a significant increase in LH pulse amplitude (P < 0.05). Strolling produced no significant changes in LH secretion. CONCLUSION Acute exercise of moderate Intensity in the follicular phase of untrai ned women is an insufficient stimulus to inhibit the GnRH pulse genera tor in the post-exercise period, yet may produce a slight stimulatory effect on the amount of LH released per pulse.