Barry A. Turnbull

Induction of Menstrual Disorders by Strenuous Exercise in Untrained Women

We performed a prospective study of 28 initially untrained college women with documented ovulation and luteal adequacy to determine whether strenuous exercise spanning two menstrual cycles would induce menstrual disorders. To ascertain the influence, if any, that weight loss might exert, we randomly assigned the subjects to weight-loss and weight-maintenance groups. Subjects were expected to run 4 miles (6.4 km) per day, progressing to 10 miles (16.1 km) per day by the fifth week, and to engage daily in 31/2 hours of moderate-intensity sports. The normalcy of the menstrual cycles during the period of exercise was judged independently according to clinical and hormonal criteria, the latter comprising serial measurements of gonadotropin and sex-steroid excretion. A higher percentage of abnormalities proved to be detectable by hormonal means (P less than 0.02). Only four subjects (three in the weight-maintenance group) had a normal menstrual cycle during training. In the weight-loss group, the number of women who had luteal abnormalities as compared with those who lost the surge in luteinizing hormone altered significantly over time, the latter occurring more frequently (P less than 0.01) as training progressed. Within six months of termination of the study, all subjects were again experiencing normal menstrual cycles. We conclude that vigorous exercise, particularly if compounded by weight loss, can reversibly disturb reproductive function in women.

Strenuous exercise with caloric restriction: effect on luteinizing hormone secretion.

To test whether strenuous exercise with and without caloric restriction alters LH secretion, and whether these changes are apparent in the immediate post-exercise period, LH pulse parameters were studied in four moderately trained eumenorrheic women over three successive menstrual cycles. Blood samples were obtained 5 h before and 5 h after 90 min of running at 74% VO2max. Each test was preceded by a 7-d treatment of controlled diet and exercise (74% VO2max). During CONTROL, subjects were eucaloric on days 1-7, and performed no exercise on days 5-7. During STTI (short-term training increase), subjects were eucaloric and completed 90 min runs on days 5-7. During DIET/STTI, subjects consumed 60% of the calories necessary to maintain weight on days 1-7, and exercised as in STTI. A significant decrease in overall (0700-1830 h) LH pulse frequency during DIET/STTI compared with CONTROL and STTI treatments was observed. No changes were found in mean serum LH levels or peak amplitude. These results suggest that high-volume training combined with caloric restriction may predispose one to exercise-induced changes in LH pulse frequency, while adequate caloric intake may prevent these changes.

Effects of short-term strenuous endurance exercise upon corpus luteum function.

PURPOSEnThe present study tested whether short-term, abruptly initiated training can cause corpus luteum dysfunction when exercise is limited to either the follicular or luteal phase of the cycle.nnnMETHODSnReproductive hormone excretion and menstrual characteristics were studied in sedentary women who exercised only during the follicular (N = 5) or the luteal (N = 4) phase. Six women served as controls, three of whom exercised at a low volume and three who remained sedentary. Weekly progressive increments in exercise volume continued until either ovulation (follicular group) or menses (luteal group) occurred. Physical activity and nutrient intake were closely monitored with the intent to maintain body weight.nnnRESULTSnNo luteal phase disturbances occurred in any of the control subjects, whereas 40% of follicular and 50% of luteal exercisers experienced luteal defects. The proportion of menstrual cycles disrupted was not different between luteal and follicular exercisers (50% vs 30%, respectively) but was significantly greater than the proportion of cycles disrupted in control subjects (P < 0.05).nnnCONCLUSIONSnThese results suggest that exposure to abrupt onset of training can alter luteal function, regardless of the menstrual cycle phase in which exercise occurs. This study also demonstrates that a relatively low volume of exercise suffices to induce mild disturbances in luteal function.

Effects of follicular phase exercise on luteinizing hormone pulse characteristics in sedentary eumenorrhoeic women

OBJECTIVE Current studies reveal little regarding the Inception of exercise‐induced LH changes during physical training. This study aimed to assess the susceptibility of the hypothalamic–pituitary axis to the acute physical stress of exercise in untrained, physically inactive women. The acute effects of submaximal endurance exercise upon the pulsatile LH secretion in the follicular phase were compared with those accompanying leisurely strolling for a similar time period.

The effects of submaximal endurance exercise upon LH pulsatility.

The acute effects of submaximal endurance exercise (three consecutive 20‐min runs on a treadmill at 50,60 and 70% of the subjects maximum oxygen uptake) upon the pulsatile release of LH were compared with those accompanying leisurely strolling for a similar period in seven normally menstruating young women. All trials were conducted during the early to mid‐luteal phase, as determined by body temperature patterns, ultrasonic scans of the ovaries, detection of the LH surge in first morning urine specimens, and serial measurements of plasma progesterone. Blood was sampled every 10 min via an indwelling cannula for 8 h before and 12 h after exercise and serum LH measured by radioimmunoassay. LH pulsations were analysed by a time series method. Following cannulation, mean LH levels declined but then rose to reach a maximum 2 h before the beginning of the exercise bout. LH concentrations remained virtually unchanged during exercise itself, and exhibited a declining trend throughout the post‐exercise period. The findings in the two groups were similar in all respects, except that in the control study the rate of LH pulsatility was significantly diminished (P<0.05) during the first 2 h of sampling as compared with the subsequent 2‐h period. The approximate half‐life of LH varied from 27 to 57 min, with a mean of 41 min.

The Detection of Peaks in Luteinizing Hormone Secretion

Fluctations in luteinizing hormone are believed to consist of irregularly spaced sharp increases separated by periods of exponential decay. A simple method is presented for analysing such fluctuations when the data consist of uniformly sampled observations of hormone. Specific allowance for the exponential decay in the absence of pulses is made via a time series model before assessing the number and extent of pulses. All calculations are done using MINITAB regression programs. The results have been compared with those obtained by three established models and are in general agreement.