Events such as these prompted several researchers to evaluate the effects of one-sixth (or lunar) gravity on the cost of work in a pressure suit. Results, however, were inconclusive. Predictions were made that metabolic costs would decrease with subgravity walking. Other researchers predicted metabolic increases would accompany low traction exercise. Other uncertainties arose from the considerations of lunar terrain and surface composition and their effect on mobility and metabolic rate. In response to these uncertainties, conservative biomedical estimates of the life support requirements were defined on the basis of available data. Although metabolic rates were not measured during the Gemini EVAs, it was clear in several instances that crewmen worked at levels above the heat removal capability of the gas cooled life support system. The Metabolism and Heat Dissipation experiment was therefore performed to determine life support requirements during Apollo EVAs.
Two types of task identification methods were used for separating the activities performed during EVA periods. For the first method, the metabolic rate monitors divided the operational tasks into four types of activities of importance to mission planners: overhead activities (those tasks required for each EVA, such as egressing and ingressing the vehicle), deploying the Apollo lunar surface experiment package (ALSEP), making geological surveys, and riding in the lunar roving vehicle. The oxygen and LCG measurement methods could be used to obtain accurate metabolic rates for these activities. The second method of task separation was based on a time and motion study which required dividing the tasks into as many definable activities as possible. However, this method resulted in some activities of such short duration that metabolic rates could only be assigned using the postflight heart rate method. Metabolic rate measurements were determined for both lunar surface EVAs (Apollo missions 11, 12, and 14 through 17) as well as zero-G EVAs (Apollo missions 9, 15, 16, 17).
Metabolic rates were lower than predicted before the Apollo missions for lunar surface EVAs. Overhead activities consumed the most energy, while driving or riding in the lunar roving vehicle consumed the least. This was comparable to shirt sleeve riding in an automobile. The highest average metabolic rate was experienced by one Apollo 11 subject who was very active in evaluating modes of locomotion. For discrete activities, the highest metabolic rates were associated with his transport of the ALSEP pallet, ingress to the Lunar Module (LM) with lunar samples, and drilling and removal of drill bits.
For the Apollo 14 mission, which included some of the most extensive walking traverses, a specific effort was made to correlate metabolic rate and traverse rate. However, data obtained showed poor correlation. The crewmen apparently maintained a comfortable walking effort and, to a large extent, the rate of traverse at this level of effort varied with the terrain and the operational requirements of each traverse. In general, both the speed and efficiency of lunar walking were greater than could be achieved while wearing a pressure suit in a 1-G environment, but neither speed nor efficiency was equivalent to that of a shirt sleeve operation in 1-G.
Operational film and kinescope were used in performing a time and motion study of Apollo 15 and 16 activities. Results from observations of Apollo 15 and 16 time and motion studies indicated that tasks were completed more rapidly at 1-G wearing space suits than at one-sixth-G, but at higher metabolic rates.
The zero-G EVA activities were measured using the heart rate method. This method tended to yield higher estimates of metabolic rates therefore results ranging from 150 to 500 kcal /hr were considered maximum values. Voice data did not indicate that the crewmen were performing strenuously. In some cases, the actual metabolic rates were much lower than the values obtained by means of heart rate calibration data. Excitement, rather than physical exertion, was considered the cause of elevation of heart rates.
The crewmen were able to perform planned EVAs and to extend them to the maximum time allowable without medical problems. The manually controlled Liquid Cooling Garment was effective in minimizing fatigue and water loss from sweating during EVA. Gas cooling was adequate during the short zero-G EVA performed from the Command Module. It was found that adequate body restraints, realistic zero-G preflight training in a water immersion simulator, and detailed planning of activities were essential to ensure completion of tasks and reduce fatigue.