Shaving and Perception of Cutaneous Sensation
Given the large surface area and the millions of sensory receptors it contains, the skin has an enormous potential to communicate information of the external environment to the spinal cord and brain. At the spinal cord level, the afferent sensory signal is subject to many neuronal inputs that serve to modulate sensory perception and, ultimately, muscle output. Thus, any mechanism serving to modulate sensory information has the potential to also affect motor output. Therefore, our first question was to determine if shaving the arms, legs, and torso of adult men resulted in an altered perception of skin sensation.
Sensory perception threshold force in ten men (26±3.6 yrs) was identified before and after shaving, with and without wind being blown across the skin. To measure sensory threshold force, Semmes-Weinstein monofilaments were applied perpendicular to the skin area overlaying the calf, and a single verbal response of “yes” was sufficient to qualify as positive perception. Applying monofilaments of differing force in an ascending and descending fashion yielded a perception threshold. After the pre-shave trial, both legs were completely shaved between the upper thigh and ankle. Sensory threshold procedures were repeated 24 hours post-shave. Calf skin temperature was measured for each experimental condition.
Pre-shave sensory threshold force was significantly greater with wind than that without wind. However, post-shave sensory threshold force was not significantly different with or without wind. Without wind, sensory threshold force before and after shaving did not differ. However, in the presence of wind, pre-shave sensory threshold force was significantly greater than post-shave. Skin temperature was not different from pre- to post-shave, and therefore did not account for the differences in perception.
Figure 1. Sensory perception threshold force (grams) graphed by conditions of shave and wind. A significant two-way interaction was found between the shave condition and wind condition. The pre-shave plus wind trial required a significantly greater force to evoke perception of a stimulus when compared to all other treatments. Error bars = ±1SEM.
In the current study, the perception of cutaneous sensory input as a result of air flowing over the skin was shown to be facilitated post-shave. Reasons for this result are likely complex, but may be understood if moving leg hair serves as "white noise" or as a distraction from the sensory task. This form of over stimulation or irrelevant sensation would prevent the task-related sensory information from being fully realized as it "steals" some of our capacity to integrate and perceive specific sensory information. Much like a decrease in driving performance while talking on a cell phone (Strayer, 2003), moving leg hair may inhibit attentiveness to the performance task and prevent the subject from perceiving the stimulus. Thus, removing hair may facilitate perceptual sensibility and enhance perceptual motor skill, which may lead to improved propulsive and streamline mechanics.
Perceptual motor skill, defined as the conscious modification of movement in response to sensory perception, may provide further insight into the current findings. Crucial for modifying movement, perceptual motor ability draws upon all of the skin senses to varying degrees in order to form a mental picture of the location, configuration, and movement of the body in space and time. Within the context of the current study, sensory input from the hair inhibits perception and thus removal of hair would enhance perceptual motor skill. Enhanced motor skill may improve a swimmer’s stroke mechanics, thereby increasing propulsive force or reducing resistance and improving performance.
Alternatively, perhaps the performance improvement post-shave is not neurophysiological, but a physical reduction in resistance. Sharp & Costill (1989) tested male collegiate swimmer's distance per stroke, heart rate, and post-exercise blood lactate concentration during a 400 yard breaststroke swim both before and after shaving. The same variables were measured during a tethered swim. In addition, the rate of velocity decay after an underwater leg push-off was measured. There was a significant increase in distance per stroke and decrease in heart rate and blood lactate post-shave during free swimming, but not tethered swimming. Further, subject's maintained a greater push-off velocity post-shave as compared to pre-shave. The author speculated that the absence of changes in physiological variables during the tethered swim and a reduction in rate of velocity decay post-shave was a result of a reduction in active drag. However, it is important to note that neither physiological cost of swimming nor active drag were measured in this study, passive drag was measured. Passive drag is the drag a swimmer encounters when the body is in a fixed position (i.e., streamlining off the wall). Active drag, on the other hand, is the drag a swimmer encounters when actively stroking or kicking. Additionally, the use of competitive swimmers is inherently biased as they expect, based on previous experience, a positive response to shaving. Therefore, the mechanism by which shaving improves performance remains unknown.
Shaving down has been an essential component of swimmers’ pre-championship ritual for years. However, the emergence of full body swim suits and full leg swim suits led some swim suit manufacturers to claim that their swim suit makes it unnecessary for a swimmer to shave. The recommendation that swimmers “need not shave” due to new suit technology has to be evaluated within the context of the potentially positive neurological effects. If removal of hair eliminates undesirable sensory input or “noise” then perhaps the suits act as a barrier disconnecting the skin from the water and thereby achieving a similar effect as shaving. Regardless, with the recent ban on full body swim apparel, the question of the effect of shaving down is pertinent because of its continued widespread practice.
Within the limitations of the study the following conclusions are warranted:
1. Cutaneous sensory perception is facilitated by shaving.
2. This 'shaving effect' only occurs with ongoing background cutaneous perturbation (wind).