Editor's Note: The product described in this article is no longer manufactured by Camelbak, but as of this writing Nashbar has them, and for almost half-off, on a closeout. As of today (October 24, 2001) they have 28 left. The link to the page in Nashbar is here.

Regarding the article below, we checked on a particular protocol issue about which we had a question. Water was provided for both of the two "rides," and in the same amounts. The only difference is that the water was colder during the Aero Bak "ride" (you can make an Aero Bak into an Ice Bak by the removal of part of the unit separating the bladder from the rider) than during the non-Aero Bak ride. This is a defensible protocol, since in real-life a water bottle is going to heat up, whereas an Ice Bak will stay cold. Whether the decreases in core temperature were caused by the colder water ingested or the proximity of the Ice Bak to the body is an open question, although we strongly suspect the latter.

Finally, realize that there are some tables and graphs discussed below that did not make it into this article (Cycling Science is out of business, and we don't have access to the tables).

In an exercising man, the production of mechanical work from chemically bound energy is a relatively inefficient process resulting in the formation of various by-products, including considerable thermal loads. An inability to adequately dissipate the excess heat generated by the active musculature during exercise not only impairs performance but also predisposes one to heat injury. Secondly, it is known that exercise-induced dehydration also contributes to thermal imbalance, fluid-electrolyte homeostasis and increased cardiovascular work.

In addition to the above objective measures, it is known that exercise has subjective components. Research focusing on the subjective dimension has led to the notion that "knowing what people think they are doing may well be more important than knowing what they are doing". For the past two decades, knowing what people think they are doing during exercise has become synonymous with responses to the Borg Rating of Perceived Exertion scale (RPE). Numerous investigators have demonstrated that RPE is a valid and reliable measure of "what" the individual estimates the magnitude of exertion they perceive during exercise (see Appendix).

Recently, a strong argument has been made to determine how emotions play in exercise and sport. Thus, to fully understand exercise behavior, an understanding of how one feels may be an important as what one feels. In support of this concept, Rejeski introduced the "feeling scale" (Affect Scale) to assess affective responses during exercise. Specifically, this scale determines if one is feeling "good" or "bad" during exercise (see Appendix).

Interest in methods of external body cooling has been prompted by all too frequent occurrence of disabling or even fatal exertional heat injury. Many studies have shown where neck and head cooling devices attenuates the rise in body temperature and may, in fact, be more efficacious in reducing heat stress than cooling of equal surfaces of other body areas. However, the cooling devices investigated in previous studies were specifically designed for industrial, military, or aerospace environments and are too cumbersome for use on widespread basis during recreational exercise. Furthermore, although heat disorders are most likely to occur high intensity exercise, the efficacy of such devices has been studied only during low intensity exercise.

In this study we initiated the investigation of the CamelBak IceBak Drinking System, a cooling and rehydration device, by studying its effects on heart rate, perceived exertion, affect, body weight and core temperature during strenuous exercise.

METHODS

Subjects. Nine healthy competitive male endurance athletes served as subjects. All were volunteers. Subjects maintained their normal level of physical activity during the course of the study, with the exception that strenuous exercise was not performed on the day before experimental sessions.

CamelBak IceBak Drinking System. The drinking system is comprised of a 5" x 18" medical grade fluid bag that slides into a matching shell that then straps onto your back. The side next to your body is not insulated and allows the inner fluid coolness to pass to the back. The CamelBak IceBak Drinking System is designed to conform to the subjects back while cycling. It weighs less than 6 1/2 ounces unfilled and holds up to 70 ounces of liquid. A three foot long, approximately .25" diameter hose brings the fluid supply from the bladder to the mouth. A valve tap requiring biting to open controls the flow.

Research Investigation. This psychophysiological study was conducted in a randomized cross-over fashion. On two experimental days, separated by several days apart, subjects performed a one hour ride on a Monarch ergometer at 80 rpm with a resistance setting of 2 KP. The exercise sessions were conducted in an ambient temperature of 82 degrees Fahrenheit and 50-60% relative humidity. To lessen the possibility of a placebo effect, subjects were provided with an explanation as to why the CamelBak IceBak device could conceivably exert either a beneficial or a detrimental effect on exercise performance and work stress.

On one day the subjects rode without drinking water or wearing the CamelBak IceBak device. For the other ride, the subjects rode with the CamelBak full of ice and topped off with water. The device was placed on the subjects immediately before the commencement of the ride involving cooling and drinking. Starting at the start of the ride the subjects consumed 100 ml of fluid every ten minutes during the CamelBak ride. Besides the CamelBak, only cycling shorts and shoes were worn during the exercise session.

During the ten minutes before exercise a thermistor probe (Yellow Springs Instrument, Model 401) was inserted to a depth of 12 cm and core temperature was recorded. Nude weight was recorded on a balance scale. Resting heart rate was recorded with a Polar Vantage heart rate monitor. Rating of perceived exertion and affect were also recorded before the start of the exercise sessions.

At the end of exercise heart rate, perceived exertion, affect and rectal temperature were once again recorded. Subjects were reweighed after being dried with a towel. Sweat rates were calculated from the weight differences.

Statistics. Significance of differences between experimental variables was analyzed using paired t-tests.

RESULTS

The effects of the CamelBak IceBak Drinking System are documented in Table One. Heart rates, perceived exertion and Affect at the end of exercise were significantly lower (p<0.05) while using the CamelBak IceBak Drinking System. Heart rates were eleven beats per minute lower, showing significantly less cardiovascular work. The 2.3 lower for perceived exertion, signifies that the work felt easier with the CameBak. The 2 points higher reading for Affect with the CamelBak told us that the subjects felt better while wearing the CamelBak. When subjects were asked at the end of exercise to rate the overall exercise session (one hour of riding) on Rating on Perceived Exertion and Affect the following were found. The nine subjects registered a 13.13 at end of the hour while riding with the CameBak and 14.88 with no fluids. With Affect they registered plus 2.5 for the whole hour of riding and plus 0.75 while riding with no fluids.

Rectal temperatures at the end of exercise were lower by .22 degrees Centigrade while using the CamelBak and was significant at the p<0.1 level. In addition, the subjects lost only 0.3 pound of weight while riding with the CamelBak IceBak and drinking fluids compared to 2.5 pounds while not riding with the CamelBak and drinking no fluids.

DISCUSSION

A variety of psychophysiological attributes combine to make the CamelBak IceBak Drinking system an ideal product for external cooling and for providing fluid replacement during exercise in the heat. From a scientific standpoint, our study is the first to demonstrate that a cooling and drinking device is capable of reducing physiological and psychological stress during high intensity exercise in a relatively hot and humid environment. Moreover, our study shows that such reduction in thermal stress can be achieved with a device practical enough for use on a widespread basis during recreational and competitive exercise.

In conclusion, we have demonstrated that a back cooling device that also allows the subject to drink cool fluids during exercise, induces significantly lower heart rates and the perception of work stress during exercise in the heat. Although the reduction in core temperature may be small, it is in a direction of potential benefit. On the basis of the present observations, and in view of the millions of individuals who exercise in the heat, it appears that the CamelBak IceBak Drinking System will reduce thermal stress and can lead to improved performance.

APPENDIX

Affect Scale While participating in exercise it is quite common to experience changes in mood. Some individuals find exercise pleasurable, whereas others find it to be unpleasurable. Additionally, feeling may fluctuate across time. Scientists have developed a scale to measure such responses. The scale is presented in an 11 point bipolar good/bad format, ranging from +5 to -5. Verbal anchors are provided at the 0 point, and at odd integers +5 = very good, +3 = good, +1 fairly good, 0 = neutral, -1 = fairly bad, -3 = bad, and -5 = very bad.

Rating of Perceived Exertion (RPE)

While you are exercising it is quite common to have a sense for how hard you are working. By using this scale, stimuli from muscles, respiratory effort, pain, psychological stress and heat stress can be perceived and evaluated during exercise. By re-creating these efforts at any time, you can reproduce that same level of exertion under various exercise and environmental conditions.

Studies by Dr. Gunnar Borg, showed that the sensory stimuli generated during exercise or work are integrated by the brain into a perception of effort. Subsequent studies by Dr. Borg and others have shown that these "subjective" estimates of effort are highly related to workload and heart rate. In other words, your subjective estimate of effort provides a rather accurate estimate of workload, as well as the physiological factors affected by the exercise session.

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Edmund R. Burke, Ph.D.
3240 Wade Court
Colorado Springs, CO. 80917-5832
Phone and Fax: 719-380-1473
Email: eburke@sportscience.com