| Nomadic Ngisonyoka Turkana experience seasonal stress resulting from pastoralism in a hot, semi-arid, resource-limited environment. They herd despite an extended seasonal drought during which food and water resources are patchy and unpredictable. Successful exploitation of this environment requires strategic herd management, opportunistic mobility, a flexible social system, and physical work capacity (PWC) equal to the demands of herding and watering livestock and moving encampments. They may move 100 km annually, while seasonal food shortages affect nutrition and ultimately health, energy reserves, and PWC. Since they participate minimally in a market economy, surviving instead by their own physical labor through animal husbandry, it is important to understand how they respond as the dry season progresses and their condition deteriorates.; This study investigated the relationship between changing body energy reserves and PWC. Seasonal changes in body weight and arm and leg muscle and fat volumes were related to changes in resting metabolic rate and peak aerobic power in Ngisonyoka males aged 20-44 years.; The Ngisonyoka studied accomplished their work by responding on two levels. First, they used behavioral strategies to minimize daily exposure to heat stress and dehydration. Nonetheless, they appeared capable of working in the heat while chronically dehydrated and ketotic.; The second response level involved longer-term cultural mechanisms tied to relative age ranking and physical abilities. These were employed to temporally distribute nutritional and work-related stress. The result: some age groups, notably the 20-29 year-old herders, bore a greater share of the stress. These men performed critical tasks during the 1984-85 drought, but had greater access to food resources. Occupation and wealth, which crosscut age groups, also modified individual energy balance and PWC.; Recovery of lean body mass (LBM) following seasonal starvation seemed swift in the 20-29 year-old herders, as was an apparent training-related increase in arm muscle volume. Activity and an earlier restoration of muscle than fat volume may be mechanisms whereby LBM is maintained over several years of cyclical weight loss. |
