Aetiological approach of female reproductive physiology in lactational amenorrhoea.

The duration of postpartum amenorrhea and return of ovulation varies on an individual and population basis. In 1980, in Senegal, the relationship of chronic malnutrition and female fertility was investigated for 2 years. The stability of the female body regarding weight and arm circumference despite a heavy annual workload was a surprising finding. The mean female body mass index was higher for lactating women in amenorrhea than required for restoring menstruation in European women. The mean duration of postpartum amenorrhea was 18.2 +or- .6 months. The difference between those who resumed menstruation (20.9 +or- .9 months) and who still had amenorrhea (25.4 +or- 2.2 months) was significant. The duration of breast feeding determined the duration of amenorrhea. Studies have found a link between ovarian dysfunction and women in harsh third world environments and sportswomen under intensive training with both showing irregular menstruation and amenorrhea. Long duration of cycles in New Guinean women, high amount of anovulation in Zairian forest women, and suppression of testosterone and estradiol levels in hunter-gatherers were found. In affluent Europeans and urbanized women in developing countries postpartum amenorrhea dropped drastically. Long distance runners are often vegetarians with low calorie consumption and with a high degree of menstrual trouble owing to low body fat and weight-for-height. The role of beta-endorphins in the hypothalamic blockade of the gonadotropin releasing hormone pulse generator and high stress or physical training is proven. The functioning of the hypothalamo-pituitary-ovarian axis can be hurt by intensive training. Short-term fasting also suppressed the pulsatile luteinizing hormone and testosterone secretion. The protocol and methodology of an etiological study is outlined regarding the factors of this hypothesis on amenorrhea.     

Effects of testosterone on sexual behavior and morphology in adult female leopard geckos, Eublepharis macularius.

The leopard gecko, Eublepharis macularius, is a species in which testosterone (T) is the primary circulating sex hormone in adults of both sexes. There are, however, sex differences in T physiology. Whereas males have prolonged periods with high T levels, T levels cycle in accord with follicular development in females. Specifically, T concentration increases during vitellogenesis, drops after ovulation, and then remains at previtellogenic levels until eggs are laid and the next follicular cycle begins. To determine the function of T in females, we manipulated both the level and the duration of T elevation using Silastic implants in intact, adult female leopard geckos. Females had low ( approximately 1 ng/ml), medium ( approximately 100 ng/ml), or high ( approximately 200 ng/ml) T levels for either a short (8 days) or a long (35 days) duration. Behavior tests with males were conducted on days 1-5 in the short-duration group or on days 29-33 in the long-duration group. For both short- and long-duration groups, T treatment decreased attractivity in females with medium and high T levels compared to females with low T levels. In contrast, females with a medium T level were more receptive than females with a low T level in the short-duration group. Females in the long-duration group were unreceptive regardless of T level. Females treated for a long duration also displayed more aggression toward and evoked more aggression from males than short duration females. Short-duration T treatment had no masculinizing effect on female morphology, whereas medium and high T levels for a long duration induced development of hemipenes. Overall, these results suggest that T can both increase and decrease sexual behaviors in the female leopard gecko.     

Postpartum lactational amenorrhoea as a means of family planning in the Sudan: a study of 500 cases

The lactational histories of 500 Sudanese women were studied retrospectively to examine postpartum lactational amenorrhea as a method of family planning. Particular attention was given to the factors affecting postpartum lactational amenorrhea, including supplementary feeding and the use of modern contraceptive methods. Breast-feeding was overwhelmingly practised (90%) among this sample, which was roughly representative of the Sudanese population as a whole. The prevalence of amenorrhea among this group of lactating women was quite high (73%). Duration of lactational amenorrhea ranged from 2 to 36 months with a median of 12 months. Introduction of supplementary feeding had little effect on lactational amenorrhea up to the 9th month of breastfeeding. Beyond the 12th month of breastfeeding, lactational amenorrhea was significantly prolonged by postponing the introduction of supplementary feeding until the 4th month or later. Ovulation, and hence conception, during lactational amenorrhea was unpredictable. It occurred as early as the 3rd or as late as the 36th month postpartum. Conceptions interrupting lactational amenorrhea soon after delivery (3-9 months) were more frequent among primiparous women. The failure rate of lactational amenorrhea as a contraceptive was 8.4%. Though extremely high compared to that of the pill, lactational amenorrhea was more useful as a fertility control mechanism because, in this study, a high proportion of women initiated pill use, but soon discontinued it because of side effects. Modern contraceptive practice was not prevalent. Amenorrheic mothers accepted the pill after the 6th month postpartum (41%, compared to lactating mothers whose menses had returned who started much earlier. 49% of the women studied relied completely on the protection of lactational amenorrhea. 57% of all lactating women who used the combined pill reported a reduction in milk production. Knowledge of modern contraception was poor and incorrect in many cases, leading to several policy implications, including usage of sterilization.     

Social and seasonal influences on the reproductive cycle in female mandrills (Mandrillus sphinx)

We present 12 years of perineal swelling data for a semifree-ranging colony of mandrills (Mandrillus sphinx), and evaluate the influence of rank, parity, and seasonality on reproductive parameters. Female sexual swellings showed a seasonal pattern, with August the median month of ovulation. Overlapping periovulatory periods did not decrease the likelihood of conception. Females showed their first genital swelling at age 3.6 years (n = 28; range, 3.2-4.6 years), and higher-ranking females experienced their first swelling earlier than low-ranking females. Median postpartum amenorrhea (PPA) duration was 208 days (n = 92; range, 74-538 days). PPA was longer in primiparous females than in multiparous females, but PPA duration was unrelated to female rank. Median follicular phase duration was 24 days for the first cycle after parturition (n = 84; range, 12-40 days), shortening to 17 days in subsequent cycles (n = 55; range, 6-39 days). The follicular phase was longer in nulliparous females than in parous females, but was unrelated to female rank. Median cycle length (from one sexual swelling breakdown to the next) was 38 days (n = 57; range, 18-108 days). Eighty-seven percent of conceptions occurred within two cycles, and half of the nulliparous females conceived during their first swelling cycle. Lower-ranking females were more likely to require more cycles to conceive than higher-ranking females. The cycling phase was significantly longer in nulliparous females than in parous females, and was also significantly longer in lower-ranking females than in higher-ranking females. We discuss the influence of provisioning on female reproductive parameters, the influence of parity and rank on the different phases of the interbirth interval, and the evolution of long and variable follicular phases in mandrills.     

Resumption of menstruation among urban post-partum women in Bangladesh.

To investigate the return of menstruation among postpartum women in Dacca, a random sample of 360 women (1-12 months postpartum) was selected from 4 Dacca hospitals for a cross-sectional study; another random sample of 200 women ( 1 month postpartum at time of interview) was selected from the same hospitals for prospective follow up. Many of the women were from rural areas who left the city after delivering their babies; most were under 25 years old at the time of interview. Results of the cross sectional study showed that 63% started menstruating by the 6th postpartum month; 10% were still amenorrhoeic by the 12th postpartum month; 46% were breastfeeding their infants by the 4th month; 90% resumed sexual relations, and 48% were using contraceptives, by the 6th month. Results of the prospective study showed that slightly more than half of the women started menstruating by the end of the 5th postpartum month; almost half stopped breastfeeding by the 5th month, 88.8% were having sexual relations with their husbands, and about 50.5% were on some form of birth control. The findings suggest a much shorter duration of lactational amenorrhea than has been claimed for a rural area of Bangladesh; they also suggest that urban women start menstruating earlier because of their primary reliance on supplementary feeding. The contraceptive effectiveness, as well as health benefits to infants, of prolonged and intensive lactation should be promoted to urban mothers.     

Blood flow response to muscle contractions is more closely related to metabolic rate than contractile work.

The magnitude of the blood flow response to exercise has been linked to both the contractile work performed and the metabolic cost of the activity. Under certain conditions, contractile work and metabolic cost may be dissociated. This study examined the blood flow response to trains of contractions when contraction duration was manipulated under conditions of similar tension-time indexes (isometric analog of work). Previous investigations have shown that trains of short-duration contractions have a greater ATP utilization, which may result from an augmented ion transport required for muscle activation and relaxation. On the basis of these findings, we hypothesized that the blood flow response would be greater to a train of short-duration contractions than a train of long-duration contractions. Canine gastrocnemius-plantaris muscle (n = 8) was isolated, and blood flow assessed with an ultrasound flow probe placed around the popliteal artery. The sciatic nerve was stimulated to produce two contraction protocols that resulted in similar contraction-to-rest ratios: short duration: 0.25 s/0.75 s vs. long duration: 1 s /3 s. In accord with the design of the experiment, the tension-time indexes were identical for the two contraction protocols (short: 18.6 +/- 1.0 vs. long: 18.6 +/- 1.0 kN.s). Steady-state oxygen consumption was greater in the short-duration contractions (17.2 +/- 0.9 ml.100 g(-1).min(-1)) than in the long-duration contractions (11.7 +/- 0.7 ml.100 g(-1).min(-1)). Similarly, the steady-state blood flow was greater in contractions of short duration (125 +/- 7 ml/min) compared with long-duration contractions (92 +/- 7 ml/min). Contractions of short duration resulted in significantly higher oxygen consumptions and blood flows compared with contractions of long duration despite the same total contractile work. The blood flow response to muscle contraction appears to be more closely associated with muscle metabolism than contractile work performed.     

Nutrition, infant feeding and post-partum amenorrhoea in rural Bangladesh

The extent to which differences in the duration of postpartum amenorrhea among chronically malnourished women in rural Bangladesh are related to seasonal patterns of food supply, maternal nutrition, education, and patterns of infant feeding was investigated by application of multivariate hazards models with time-varying covariates. The data were derived from the Birth Interval Dynamics study in Matlab and covered close to 1800 births. Parity, education, season of birth, maternal weight, and infant supplementation all were found to affect the duration of postpartum amenorrhea among these women. Education of 5 or more years had a positive effect on the resumption of menses. Higher parity women, who were older, had longer periods of amenorrhea, as did women who gave birth in October-December. As a measure of nutritional status, the woman's weight at pregnancy termination showed a highly significant positive coefficient, indicating that improved maternal nutrition increased the likelihood of resuming menstruation. Food supplementation, which tends to decrease breastfeeding, also significantly increased the risk of resuming menstruation and had an effect independent of the other variables. When the data were analyzed by season, the most striking finding was the strong influence of education on children born during October-December (who are too young to be directly affected by the larger food supply at birth during the harvest season). The other seasons showed weaker effects of education and a stronger effect of supplementation, perhaps because these infants are older during the harvest season and thus can benefit from supplements.     

Development of dominant follicles and length of ovarian cycles in post-partum dairy cows

The resumption of ovarian activity after normal calvings was studied in 18 lactating Friesian cows. Since, in 17 cows, first post-partum ovulation occurred without overt oestrous behaviour being detected, the resultant cycles were called 'ovarian cycles'. The mean (+/- s.d.) length of the ovarian cycles was 21.0 +/- 8.7 days. The duration of cycles tended to be normal (18-24 days) or long (greater than or equal to 25 days) when the ovulatory dominant follicles were identified before Day 10 post partum; they were consistently short (9-13 days) when dominant follicles identified after Day 20 post partum ovulated. When such follicles were detected between Days 10 and 20 post partum, long, normal and short ovarian cycles were detected. The number of waves of follicular growth with associated dominant follicles observed during the ovarian cycles tended to be related to cycle length; short cycles had 1 dominant follicle, normal cycles predominantly 2, and long cycles mostly 3 dominant follicles. The mean (+/- s.d.) duration of 13 oestrous cycles studied was 23.1 +/- 2.1 days. Of these cycles, 7 had 3 and 6 had 2 dominant follicles. The oestrous cycles with 3 dominant follicles had a mean (+/- s.d.) duration of 24.0 +/- 1.2 days and the respective dominant non-ovulatory follicles reached maximum sizes on Days 8 and 18, respectively; oestrous cycles with 2 dominant follicles were 22.2 +/- 2.6 days in duration, and the dominant non-ovulatory follicle reached maximum size by Day 8. Ovarian follicular development during the first 45 days of pregnancy was characterized by the growth and regression of successive dominant follicles, each lasting 10-12 days. These results show that the first ovarian cycle was predominantly short when the ovulatory dominant follicle was first detected after Day 20 post partum.     

Reproductive function in aged female chimpanzees.

Reproductive function was evaluated in ten female chimpanzees (Pan troglodytes) aged 35-48 years. Forty-eight years is the longevity record for the chimpanzee. Data on cycle frequency and duration was available for seven animals. Most were cycling regularly until death, and all had experienced at least one menstrual cycle within one year of death. After exclusion of periods when the animals were pregnant or in postpartum amenorrhea, the mean cycle frequency (+/- standard error)/year was 9.54 +/- 0.20 in seven animals aged 15-25 (432 cycles analyzed) compared to 8.6 +/- 0.76 in the same animals at age 35 + years (405 cycles analyzed); this effect approached significance (p = 0.072, Mann-Whitney U-test). Cycle length of 16 cycles in each of seven animals aged 15-25 was 32.23 +/- 0.38 days. The same animals when aged over 35 had mean cycle lengths of 35.59 +/- 0.73. This difference was not significant, although cycle lengths clearly increased with age in some individual animals. In five aged animals for which mating data was available, appropriate exposure to a male occurred in 52 cycles, but only two pregnancies occurred; one pregnancy resulted in a live birth at age 38, the other in a stillbirth at age 40. This conception rate was 3.85% compared with 20% in the same animals aged 15-25. These data suggest greatly reduced fertility after age 35, although menstrual cycle frequency remained high. The persistence of menstrual cyclicity until death, which occurred due to natural causes at latest in the fifth decade, is in striking contrast to the human female in which menopause occurs in the fifth decade and death is often postponed for several more decades.     

Nursing practices and lactation amenorrhoea

The purpose of this study is to test the hypothesis that nursing behavior is an independent underlying factor of importance in duration of amenorrhea. Multivariate analysis is applied to information on frequency and duration of nursing practices, maternal age, and nutritional status assessed by weight for height in a sample of 32 middle-class American women with a wide range of nursing behavior. The mothers were followed for 2 years postpartum, data being collected during 8 home visits by interview and by nursing records kept by the mothers. Amenorrhea lasted 1.3 to 27.1 months in the sample as a whole. Those women who nursed frequently (8/day) during exclusive breastfeeding remained amenorrheic longer than infrequent nursers, introduced supplements later, and did not resume menses as promptly thereafter. They continued an hour or more of night nursing during supplemented nursing. Duration of exclusive nursing and night nursing after supplementation were the major influences on duration of amenorrhea. This strong association favors the hypothesis that the underlying factor is nursing behavior. Mother's age, weight-for-height, and nursing frequency before supplementation showed no significant effect. Those women who introduced supplements late and maintained at least an hour of night nursing had a prolonged period of amenorrhea. The median for this group was 6-10 months longer than that for those who started supplements early and/or reduced subsequent night nursing to less than an hour. The recommendation that women must suckle their babies at least 5 times a day with a total suckling duration of more than 65 minutes per day is not sufficient. The findings reported here suggest that if women nurse exclusively for the 1st half year, maintaining night nursing after introducing supplements is important. If they supplement earlier, then they will lose the contraceptive protection of lactation, irrespective of how they nurse.     

Impact of lactation upon fertility in the New World primate capuchin monkey (Cebus apella)

In the present paper, we have studied the impact of lactation upon fertility in the capuchin monkey, Cebus apella, under laboratory conditions. Nursing females (ten females, 12 postpartum periods) presented lactational amenorrhea (first menses at 159.2 +/- 9.0 vs 42.6 +/- 5.8 days postpartum in five non-nursing females, seven postpartum periods). Plasma estradiol and progesterone concentrations during lactational amenorrhea were lower than those during the follicular phase of the menstrual cycle. Prolactin was higher than in non-nursing females at 31-60 days postpartum. Interbirth interval, studied in three non-nursing (four intervals) and six nursing females (eight intervals) lasted for 349.5 +/- 11.8 and 613.4 +/- 30.8 days, respectively. In non-nursing females, early recovery of the menstrual cycle was followed by a residual infertility (mating but no pregnancy) lasting 152.8 +/- 7.9 days. In nursing females, recovery of the menstrual cycle was followed by an extended residual infertility of 301.5 +/- 22.7 days. Thus, in the capuchin monkey, nursing prolongs the interbirth interval by inducing lactational amenorrhea and extending the residual infertility period.     

Fishing and fertility: a study of a Nova Scotia fishing village.

The relationship between fertility and occupation is compared for: 1) deep-sea fishermen who are away from home as long as 21 days at a time with short rests between; 2) in-shore fishermen who are away at sea most nights; and 3) plant workers in the locality, used as controls. Particular attention was given to the families of fishermen who had done the same job since marriage. The population was old, relatively speaking, due to outmigration of younger people. 73% of the wives were over 30 years of age. Deep-sea fishermen are younger and have higher incomes than in-shore men (42.1 years vs 49.7 and $3544 vs $2900). Among women 15-44 years of age mean number of children for deep-sea fishermen was 3.35; in-shore, 3.60; plant workers, 3.62. Among those whose husbands had held the same job since marriage the variation was greater: deep-sea, 2.54; in-shore, 3.46; plant workers, 3.35. Among women over 45-years-old whose husbands had held the same job since marriage the number of children was 2.61, 3.94, and 4.27, respectively. 33% of plant workers had more children than desired and 66.7% said they had as many as desired. However, 25.9% of in-shore fishermen and 50% of deep-sea fishermen had fewer than desired. Interval between births was similar for all occupational groups (23.5-26.7 months) but the wives of deep-sea fishermen terminated childbearing earlier. Contraception was used only by the younger women, usually coitus interruptus or rhythm. Sterilization may have been important but it was hard to find out whether the 15% of wives who reported operations which made further childbearing impossible intended sterilization. 35.7% of deep-sea fishermens' wives reported such operations, generally women with larger families.     

Weaning, body weight, and postpartum amenorrhea duration in pigtailed macaques (Macaca nemestrina)

Early permanent infant separation or weaning decreases the time interval between pregnancies and interbirth intervals for many female primates. At least part of the interpregnancy interval consists of postpartum amenorrhea, a period of non-menstruation lasting from the time of birth until the female begins to ovulate. This study investigated the effects of weaning age and dam's body weight on the duration of the interval between pregnancies, the duration of postpartum amenorrhea, and the number of cycles to conception in a year-round breeder. Female pigtailed macaques (Macaca nemestrina) have an observable perineal swelling that fluctuates throughout the menstrual cycle and provides a means of detecting ovulation. The perineal swelling records of socially housed pigtailed macaques were studied from July 1996 to September 1998. Postpartum amenorrhea data were obtained on 44 females who gave birth to normal, viable infants. As weaning age increased and dam's weight decreased, postpartum amenorrhea, and consequently the interval between pregnancies, increased in duration. The interpregnancy interval consisted almost entirely of the postpartum amenorrhea phase. Our finding that a higher dam's body weight decreased the length of postpartum amenorrhea duration lends support to the hypothesis that a minimum body weight is necessary for menstrual cycles to occur. Most females became pregnant on their first ovulation regardless of weaning age and whether or not they were carrying an infant. As the weaning age of the infant and the dam's weight increased, ovulation went from occurring after separation to occurring before separation.     

The diving behavior of blue and fin whales: is dive duration shorter than expected based on oxygen stores?

Many diving seabirds and marine mammals have been found to regularly exceed their theoretical aerobic dive limit (TADL). No animals have been found to dive for durations that are consistently shorter than their TADL. We attached time-depth recorders to 7 blue whales and 15 fin whales (family Balaenopteridae). The diving behavior of both species was similar, and we distinguished between foraging and traveling dives. Foraging dives in both species were deeper, longer in duration and distinguished by a series of vertical excursions where lunge feeding presumably occurred. Foraging blue whales lunged 2.4 (+/-1.13) times per dive, with a maximum of six times and average vertical excursion of 30.2 (+/-10.04) m. Foraging fin whales lunged 1.7 (+/-0.88) times per dive, with a maximum of eight times and average vertical excursion of 21.2 (+/-4.35) m. The maximum rate of ascent of lunges was higher than the maximum rate of descent in both species, indicating that feeding lunges occurred on ascent. Foraging dives were deeper and longer than non-feeding dives in both species. On average, blue whales dived to 140.0 (+/-46.01) m and 7.8 (+/-1.89) min when foraging, and 67.6 (+/-51.46) m and 4.9 (+/-2.53) min when not foraging. Fin whales dived to 97.9 (+/-32.59) m and 6.3 (+/-1.53) min when foraging and to 59.3 (+/-29.67) m and 4.2 (+/-1.67) min when not foraging. The longest dives recorded for both species, 14.7 min for blue whales and 16.9 min for fin whales, were considerably shorter than the TADL of 31.2 and 28.6 min, respectively. An allometric comparison of seven families diving to an average depth of 80-150 m showed a significant relationship between body mass and dive duration once Balaenopteridae whales, with a mean dive duration of 6.8 min, were excluded from the analysis. Thus, the short dive durations of blue whales and fin whales cannot be explained by the shallow distribution of their prey. We propose instead that short duration diving in large whales results from either: (1) dispersal behavior of prey; or (2) a high energetic cost of foraging.     

A comparative study of the estrogenic potential of two synthetic estrogens (mestranol and ethinylestradiol)

The purpose of this study was to establish the relative estrogenicity of ethinylestradiol and mestranol and to establish .05 and .1 mg of mestranol as standard reference preparations for the comparative study of other compounds. Patients were selected from a large group of primary amenorrhea, secondary amenorrhea, and postmenopausal women. All required hormonal replacement therapy. Patients with chromosomal abnormalities or those with diminished or abnormal response were excluded. Vaginal cytology was used as the main method for the assessment of the response. Before treatment all had either an atrophic pattern (Maturation Index = 50-50-0) or a hypertrophic pattern (MI=5-95-0) with a mean value of 10-87-3 for patients with primary amenorrhea and 18-79-3 in the other 2 groups. Patients with a proliferative intermediate cell pattern and postmenopausal women thought to have continuing endogenous estrogen activity were omitted. Ethinylestradiol or mestranol were given orally in doses of .025, .05, and .1 mg for a period of 10 days during which frequent vaginal smears were made. When cell patterns showed extremely marked cytolysis of the glycogen-containing intermediate cells and a low percentage of karyopyknotic superficial cells these patients were excluded. 40 women were finally included. The effects of estrogen on the vaginal epithelium in all 40 women after 10 days therapy were quite uniform. In those cases showing delayed regression of estrogenic effects 4 mg of chlormadinone acetate was given daily for 10 days. These patients then showed a reduction in the superficial cell percentage accompanied by a shift to the left in the maturation index such as 0-40-60 before to 0-95-5 after treatment. A few women had an insignificant reduction in the superficial cell percentages. Changes in the percentages of the intermediate type of cells were not significant. The regression was considered to be complete when the smear contained mainly small intermediate cells and parabasal cells with numerous leukocytes and some necrotic debris. Both estrogen preparations produced the same vaginal response at .05 mg doses. Tablets of .05 and .1 mg mestranol were chosen for further study. The increase in the superficial cell index to 30 (SD plus or minus 18.5) following treatment with .05 mg and the increase to 54.1 (SD plus or minus 26.7) following .1 mg have been adopted as standard vaginal responses. The term estrogenic effect used in vaginal cytology is taken to mean the local vaginal effect induced by estrogens.     

Determinants of natural fertility in Sudan

The population of Sudan (North) is at a very early stage of fertility transition and experiences high, stable fertility at a close to natural level. The high observed fertility is found to be a function of the high proportion of married women and ineffective contraceptive procedures. The data used in this study were drawn from the 1979 Sudan Fertility Survey (SUDFS), in which 3115 ever-married women 50 years old from 12,028 households were interviewed. 90% of Sudanese women breast fed for at least 6 months and 80% for at least 12. The main inhibitor of fertility is perceived to be lactational amenorrhea averaging about 11.8 months, which is reported to be high, although among younger women the duration of amenorrhea is shorter due to earlier introduction of supplementary foods. An average of 5.2 months of postpartum sexual abstinence is evidenced, but this is shorter than the period of amennorhea, and therefore has no effect on the birth interval. Neither does marital instability or mean length of separation, which are both close to nonexistent. Sudanese women are comparatively very infecund. 22% gave birth within the 1st year of marriage, 62% within the 2nd, and 83% the 3rd. The proportion of ever-users of contraception is high (e.g. 15.4% among the 25-34 among category), but current use was low (8.1% for the same). The use of contraception is responsible for a reduction of 4.2% of the fertility per married woman. The duration of temporary separation between spouses, due to temporary or seasonal migration of husbands, and the pathological causes of high primary sterility, which contribute to the low fecundability, need further investigation.     

Declines in physiological functional capacity with age: a longitudinal study in peak swimming performance.

We followed up swimming performance times of 321 women and 319 men who participated in the US Masters Swimming Championships over a 12-yr period. All swimmers placed in the top 10 in their age group over 3 yr (mean = 5 yr). A random coefficients model for repeated measures was used to derive a line of best fit from a group of regression lines for each subject. Both 50- and 1,500-m swimming performance declined modestly until approximately 70 yr of age, where a more rapid decline was observed in both men and women. Compared with 1,500-m swimming, the 50-m freestyle declined more modestly and slowly with age. The rate and magnitude of declines in swimming performance with age were greater in women than in men in 50-m freestyle; such sex-related differences were not observed in 1,500-m freestyle. Overall, the variability along a population regression line increased markedly with advancing age. The present longitudinal findings indicate that 1) swimming performance declines progressively until age 70, where the decrease becomes quadratic; 2) the rates of the decline in swimming performance with age are greater in a long-duration than in a short-duration event, suggesting a relatively smaller loss of anaerobic muscular power with age compared with cardiovascular endurance; 3) the age-related rates of decline are greater in women than in men only in a short-duration event; and 4) the variability of the age-related decline in performance increases markedly with advancing age.     

Physiological responses during interval training with different intensities and duration of exercise

The purpose of this study was to compare 4 interval training (IT) sessions with different intensities and durations of exercise to determine the effect on mean VO?, total VO?, and duration of exertion ≥95% maximum power output (MPO), and the effects on biomarkers of fatigue such as blood-lactate concentration (BLC) and rating of perceived exertion. The subjects were 12 recreationally competitive male (n = 7, mean ± SD age = 26.2 ± 3.9 years) and female (n = 5, mean ± SD age = 27.6 ± 4.3 years) triathletes. These subjects performed 4 IT sessions on a cycle ergometer varying in intensity (90 and 100% MPO) and duration of exercise (30 seconds and 3 minutes). This study revealed that IT using 30-second duration intervals (30-30 seconds) allows the athlete to perform a longer session, with a higher total and mean VO? HR and lower BLC than 3-minute durations. Similarly, submaximal exertion at 90% of MPO also allows performing longer sessions with a higher total VO? than 100% intensity. Thus, the results of the present study suggested that to increase the total time at high intensity of exercise and total VO? of a single exercise session performed by the athlete, IT protocols of short durations (i.e., 30 seconds) and submaximal intensities (i.e., 90% MPO) should be selected. Furthermore, performing short-duration intervals may allow the athlete to complete a longer IT session with greater metabolic demands (VO?) and lower BLC than longer (i.e., 3 minutes) intervals.     

A note on the determinants of breastfeeding durations in an African country

This paper utilizes data from the 1977-78 Kenya Fertility Survey, 1 component of the World Fertility Survey, to analyze the determinants of breastfeeding durations for women 15 to 50 years old who had their last-but-1 live birth between 3 and 15 years prior to the interview. Comparisons are made with the findings fro m the World Fertility Surveys in 8 other developing countries in Asia and Latin America. Findings indicate that literacy, urban residence, secondary school education, and modern employment reduce the duration of breastfeeding in Kenya. In addition, the subgroups of women who appear to be curtailing breastfeeding are growing in proportional size or are composed of women may be innovators or leaders. A continuation of this pattern into the future may increase levels of infant morbidity and mortality and, in the absence of increased modern contraceptive practice, may increase the societal level of fertility. The death of the infant curtails the period of breastfeeding. Although there is a pronounced preference for male children in Kenya, this preference does not lead to differential durations of breastfeeding by sex of child. About 10% of Kenyan women used contraception in the last closed interval. Parity and age explain less than 1% of the variation in duration of breastfeeding in Kenya. Kenyan women are among the least likely to have attended secondary school, to have worked since marriage, and to have used modern contraception. The most traditional groups of Kenyan women, those who are Muslim or who are in polygamous unions, breastfeed for the longest durations. The Kenya Fertility Survey suggests that the subgroup of women with some secondary school education is growing considerably. Kikuyu women may be regarded as innovators in many respects. In addition to having shorter breastfeeding durations, they are the least likely to be in polygamous unions or to want more children, and they are the most likely to be using contraception.