Physical activity, energy stores, and seasonal energy balance among men and women in Nepali households

Seasonal rhythms and exercise

Levels of leisure-time physical activity and physical fitness are generally higher in the summer than in the winter months for most people living away from the equator. The notion that an abrupt increase in physical activity in the spring, after a period of relative inactivity, can trigger sudden cardiac events has not been confirmed. There are seasonal variations in the physiological responses to exercise and the occurrence of injuries during participation in sports, but it is not known whether these changes are explained by fluctuations in activity levels and environmental conditions, or by any endogenous circannual rhythms in the human. There are indications of endogenous control for some physiological processes (eg, the metabolic responses to a given intensity of exercise) that seem to mediate more favorable effects of exercise on body composition in the winter. Well-trained athletes show obvious seasonality in their competitive performances, generally in line with adopted annual periodization strategies, although these strategies can be disrupted by external seasonal factors, such as heat stress or the susceptibility to upper respiratory tract infections. Maximal oxygen consumption and other physiological indicators of exercise performance might not mirror seasonal variation in real performances, which suggests that top-class athletes maintain a good level of general physical conditioning throughout the year.

Anthropometric data indicate nutritional homogeneity in Hadza foragers of Tanzania

We analyzed body mass index (BMI = wt/height(2)) and percent body fat (BF%) in adults of the Hadza, an egalitarian society with a strong food-sharing ethic, to examine variation in energetic status in relation to sex, age, and time of year. Data collected from 26 camps over six field seasons gave a cross-sectional sample of 238 males and 235 females and a small longitudinal sample (n = 54). We found that mean BMI showed no sex difference [20.1 +/- 1.6 (SD) kg/m(2) for males and 20.3 +/- 2.2 kg/m(2) for females] and remained similar, regardless of age or time of year. Mean BF% showed a significant sex difference, as expected [10.6 +/- 3.2 (SD) % for males and 19.0 +/- 7.0% for females (P < 0.0001)], with two significant age departures from uniformity: (1) males in the prime age group (30-45 years, n = 79) had a higher mean BF% (11.7%) compared to other ages (P < 0.03), and (2) females in the extreme elderly age group (> 75 years, n = 11) had a lower mean BF% (11.3%) compared to other ages (P < 0.004). In the longitudinal sample, we found no significant change over time in mean BMI or BF%. However, relative change in BF% fluctuated within individuals by as much as 20% of initial values for both sexes. Taken collectively, our results support the idea of broad nutritional homogeneity among the Hadza, but indicate that subtle, potentially important differences in energetic condition exist as well.

Nutritional status, growth and sleep habits among Senegalese adolescent girls

OBJECTIVE

To study the relation between sleep habits, nutritional status, growth and maturation in a group of African adolescent girls. The main hypothesis to be tested was that sleep length could be an effective way to spare energy, and thus malnourished girls sleep longer than normal girls.

DESIGN

Three repeated yearly surveys (1997-1999) on a subsample of girls drawn from a larger study cohort on growth at adolescence.

SETTING

The Niakhar district in the central part of Senegal.

SUBJECT

In total, 40 girls were initially drawn. Missing girls were replaced at each round by girls having the same characteristics and belonging to the same cohort.

INTERVENTION

At each round, data on pubertal development (breast stages and occurrence of menarche), growth and nutritional status were collected. Adolescents wore an accelerometer for three or four consecutive nights and days at each round.

RESULTS

At the beginning of the survey, girls were 13.3+/-0.5 y old. They were under international reference values in weight and height. Their mean sleep duration was 8.5+/-0.9 h. Their puberty status did not influence their sleep habits; however, they slept more in March than in June, which was related to the seasonal change in daylight. There was a significant relation between body mass index and sleep habits: thinner girls slept a longer time and more quietly than the more corpulent girls.

CONCLUSION

The nutritional status of these girls influenced their sleep habits: this may have been either a direct causal relation or a consequence of a protective attitude on the part of the mothers towards the frailer girls.

Energetic consequences of being a Homo erectus female

Body size is one of the most important characteristics of any animal because it affects a range of behavioral, ecological, and physiological traits including energy requirements, choice of food, reproductive strategies, predation risk, range size, and locomotor style. This article focuses on the implications of being large bodied for Homo erectus females, estimated to have been over 50% heavier than average australopithecine females. The energy requirements of these hominins are modeled using data on activity patterns, body mass, and life history from living primates. Particular attention is given to the inferred energetic costs of reproduction for Homo erectus females based on chimpanzee and human reproductive scheduling. Daily energy requirements during gestation and lactation would have been significantly higher for Homo erectus females, as would total energetic cost per offspring if the australopithecines and Homo erectus had similar reproductive schedules (gestation and lactation lengths and interbirth intervals). Shortening the interbirth interval could considerably reduce the costs per offspring to Homo erectus and have the added advantage of increasing reproductive output. The mother would, however, incur additional daily costs of caring for the dependent offspring. If Homo erectus females adopted this reproductive strategy, it would necessarily imply a revolution in the way in which females obtained and utilized energy to support their increased energetic requirements. This transformation is likely to have occurred on several levels involving cooperative economic division of labor, locomotor energetics, menopause, organ size, and other physiological mechanisms for reducing the energetic load on females.

Commercial porters of eastern Nepal: health status, physical work capacity, and energy expenditure

The purpose of the study was to compare full-time hill porters in eastern Nepal with part-time casual porters engaged primarily in subsistence farming. The 50 porters selected for this study in Kenja (elevation 1,664 m) were young adult males of Tibeto-Nepali origin. Following standardized interviews, anthropometry, and routine physical examinations, the porters were tested in a field laboratory for physiological parameters associated with aerobic performance. Exercise testing, using a step test and indirect calorimetry, included a submaximal assessment of economy and a maximal-effort graded exercise test. Energy expenditure was measured in the field during actual tumpline load carriage. No statistically significant differences were found between full-time and part-time porters with respect to age, anthropometric characteristics, health, nutritional status, or aerobic power. Mean VO2 peak was 2.38 +/- 0.27 L/min (47.1 +/- 5.3 ml/kg/min). Load-carrying economy did not differ significantly between porter groups. The relationship between VO2 and load was linear over the range of 10-30 kg with a slope of 9 +/- 4 ml O2/min per kg of load. During the field test of actual work performance, porters expended, on average, 348 +/- 68 kcal/hr in carrying loads on the level and 408 +/- 60 kcal/hr in carrying loads uphill. Most porters stopped every 2 min, on average, to rest their loads briefly on T-headed resting sticks (tokmas). The technique of self-paced, intermittent exercise together with the modest increase in energy demands for carrying increasingly heavier loads allows these individuals to regulate work intensity and carry extremely heavy loads without creating persistent medical problems.

Commercial porters of eastern Nepal: health status, physical work capacity, and energy expenditure

The purpose of the study was to compare full-time hill porters in eastern Nepal with part-time casual porters engaged primarily in subsistence farming. The 50 porters selected for this study in Kenja (elevation 1,664 m) were young adult males of Tibeto-Nepali origin. Following standardized interviews, anthropometry, and routine physical examinations, the porters were tested in a field laboratory for physiological parameters associated with aerobic performance. Exercise testing, using a step test and indirect calorimetry, included a submaximal assessment of economy and a maximal-effort graded exercise test. Energy expenditure was measured in the field during actual tumpline load carriage. No statistically significant differences were found between full-time and part-time porters with respect to age, anthropometric characteristics, health, nutritional status, or aerobic power. Mean VO2 peak was 2.38 +/- 0.27 L/min (47.1 +/- 5.3 ml/kg/min). Load-carrying economy did not differ significantly between porter groups. The relationship between VO2 and load was linear over the range of 10-30 kg with a slope of 9 +/- 4 ml O2/min per kg of load. During the field test of actual work performance, porters expended, on average, 348 +/- 68 kcal/hr in carrying loads on the level and 408 +/- 60 kcal/hr in carrying loads uphill. Most porters stopped every 2 min, on average, to rest their loads briefly on T-headed resting sticks (tokmas). The technique of self-paced, intermittent exercise together with the modest increase in energy demands for carrying increasingly heavier loads allows these individuals to regulate work intensity and carry extremely heavy loads without creating persistent medical problems.

Energy expenditure, physical exertion and time allocation among Huli-speaking people in the Papua New Guinea Highlands

OBJECTIVES

The study aimed to (1) elucidate the energetic adaptations of Huli people by comparing the three sub-populations in relation to their diversified natural and socioeconomic environment, based on energy expenditure and time allocation data; and (2) assess the applicability of a new index of physical exertion levels of activities (physical exertion index: PEI).

RESEARCH DESIGN AND METHODS

Married males and females (n = 43) were selected, including 14 from a hilly village, 13 from a flat swampy village and 16 migrants to a town. Continuous heart rate (HR) monitoring, in conjunction with minute-by-minute observation of activities, was undertaken. Total energy expenditure was assessed by flex-HR method and physical activity level (PAL) was calculated as multiples of basal metabolic rate. Observed activities were divided into 15 categories and the PEI was calculated for each: PEI = (mean HR of a categorized activity)/(flex HR) x 100.

RESULTS

No significant difference was found in PAL among the three sub-populations: 1.77, 1.92 and 1.81 for men and 1.78, 1.98 and 1.66 for women in hilly and flat villages, and a town, respectively. The comparison of the two village groups revealed that hilly terrain did not affect substantially the physical intensity of agricultural activities. On the other hand, the town migrants were engaged in sedentary paid jobs and these were less energy consuming than agricultural work. However, the different energy costs between paid jobs and agricultural work were offset by longer work time in the town group than in the two village groups (251 vs 50 or 70 min in males; 258 vs 152 or 138 min in females), resulting in similar PAL in the three groups.

CONCLUSIONS

Despite contrasting natural and social environments, no significant difference was found in daily physical activity level among the three sub-populations (two villages and a town) of Huli-speaking people in Papua New Guinea Highlands.

Daily energy expenditure of women by factorial and heart rate methods

To compare the minute-by-minute heart rate (Flex-HR) reference method with the factorial method, total daily energy expenditure (TDEE) and the pattern of daily energy expenditure (EE) were measured in nonpregnant, nonlactating women 19-40 yr of age, working at their household chores (at home, N = 20) or for remuneration in various kinds of employment (at work, N = 28). The factorial method used three data sets described in the compendium of Ainsworth et al. (CMD), FAO/WHO/UNU (FAO), and James and Schofield (J&S). Measurements were repeated on three rounds separated by 3 months. The TDEE by Flex-HR method, by round, was 9.0 +/- 2.6, 8.9 +/- 1.4, and 10.3 +/- 3.4 MJ.d-1 in the women at home and 9.7 +/- 2.3, 11.4 +/- 3.2, and 11.3 +/- 3.6 MJ.d-1 in the women at work. Values using the CMD data set were not significantly different from Flex-HR in either group in any round, but FAO and J&S data sets gave significantly lower values than both of the former methods in all rounds. The same statistical results were obtained for the patterns of activity. Since the timing of activities by the observers was the same, it is concluded that the major source of error in applying the factorial method is in the values for energy expenditure assigned to the various activities and the ability of investigators to properly judge EE from available data sets.

Seasonal growth patterns in rural Nepali children

This paper reports on the prevalence of growth retardation, the impact of seasonality on height and weight gains, and significant relationships between growth velocity, nutritional status and morbidity, for a population living at subsistence level in rural Nepal. Monthly variation in growth pattern was examined for 71 boys and girls 0-49 months of age. At the height of the monsoon season, 71% of children were moderately stunted, but none was wasted (mean -2.61 SD height-for-age and -0.91 SD weight-for-height by reference to NCHS z-score values). Measures of stunting deteriorated from moderate to severe after 1 year of age. No differences by sex or ethnicity were detected. Environmental changes from the winter to the monsoon seasons were reflected in significant losses of weight and lower weight-for-height z-scores, especially for 0-35 month-olds, although height for 12-35-month-olds continued to be gained over this period. Growth velocity was significantly related to previous growth status (thinner and shorter children did not show catch-up in height or weight) and to morbidity reported over the period of observation. The prevalence of illnesses rose six-fold from the winter to the monsoon, and children with a high frequency of illnesses experienced a significant shortfall in weight and height increments. A poor diet and recurrent illnesses explain the slow and uneven growth of these children. Despite an increase in women's agricultural workloads in the monsoon season, childcare patterns per se do not seem to adversely affect small children. Small stature through later childhood and in adults is one consequence of the growth pattern seen at these young ages.

Seasonal and sex variation in physical activity levels among agro-pastoralists in Nepal

Considerable attention has been devoted to variation in levels of energy expenditure between and within populations; these are commonly evaluated following international guidelines for grading light, moderate, and heavy physical activity levels (PAL). This study presents activity profiles by season and sex for subsistence agro-pastoralists in Nepal, comparing data for a sample of 20 men observed four times across the year with previously published data on women. Total energy expenditure (TEE) was estimated from direct minute-by-minute observation (totaling 1,679 h for men, 3,601 h for women) and measures of the energy cost of single tasks (117 for men, 168 for women). PAL were calculated and graded as multiples of predicted basal metabolic rate (BMR). Despite an explicitly egalitarian organization of labor, men achieved higher PAL than women (P <.0001), although according to international gradings, both men and women assume moderately heavy PAL in the winter and very heavy PAL in the monsoon. PAL were 1.88 and 2.22 x BMR for men in respective seasons (P <.005; TEE, 11.8 MJ/d and 13.9 MJ/d) and 1.77 and 2.0 x BMR for women (TEE, 9.1 MJ/d and 10.5 MJ/ d). High TEE values result from time-consuming work in subsistence tasks, most of which are of moderate energy cost. Results show that the international guideline (FAO/WHO/UNU [1985]) for grading levels of energy expenditure, which adopts discrepant sex-specific values to define thresholds for moderate or heavy PAL, can mask significant gender variation. Male/female ratios of PAL values are suggested instead for population-level comparisons.