The influence of clothing weight and bulk on metabolic rate when wearing protective clothing

Protective clothing is worn in many industrial and military situations. Although worn for protection from one or more hazards, the clothing can have secondary effects which may limit the ability of the worker to perform the tasks required of the job. Protective clothing can add significantly to the metabolic (energy) cost of work. Suggestions put forward as to the mechanisms behind the observed increases include, the additional clothing weight of the protective garments, the number of layers that must be worn and restriction of movement due to clothing bulk. However despite much speculation these areas have not received much investigation. The aims of this study, were to look at the effects of carrying weight close to the body centre of gravity and at the extremities and also to estimate the bulkiness of a selection of protective garments and how that might relate to the increased metabolic rate wearers may incur. Eleven weight configurations were tested for the first part of the study, with weights of 2 to 10 kg carried around the waist. Weights of 2 and 4 kg were also carried around the ankles or wrists (1 or 2 kg on each limb) and weights of 4 and 8 kg carried around the ankles and wrists (1 or 2 kg on each limb). The increases in metabolic rate (measured by indirect calorimetry using a Cortex MetaMax analyzer) were compared to a control condition after participants had walked at 5km/hr on a treadmill and completed an obstacle course. There was a fairly linear increase in metabolic rate as the weight carried around the waist increased. A larger increase in metabolic rate was recorded when the weight was carried around the wrists and an even larger increase when the weight was on the ankles. The clothing bulk was measured at 3 sites; upper arm, torso and thigh on six protective clothing ensembles, that had been worn in a previous study that had looked at the increase in metabolic rate when working. There seemed to be a relationship between clothing bulk in the legs and the scale of previously recorded metabolic rate increases.