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March 2004 Vol. 19, No. 3   RSS Feed for Undercurrent Issues
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Exercise Before, During, and After Diving

there are DCS risks, indeed

from the March, 2004 issue of Undercurrent   Subscribe Now

Divers should be physically fit. Not only are fit divers better prepared to handle the rigors of scuba, but also they are less likely to develop detectable gas bubbles.

Yet, while regular exercise and proper conditioning are in the diver's best interest, certain types of exercise before, during, and after a dive cause changes that may predispose a diver to DCS. While there are unknowns, there are enough theories, anecdotes, and research to provide guidelines for healthy divers observing recreational profiles.

Why the worry over exercise?

The goal of slow ascents and safety stops is to safely eliminate excess nitrogen from blood and extravascular tissue in the dissolved state as it was absorbed. Improper exercise may impede this by contributing to bubble formation, the root cause of DCS. While it is as yet uncertain whether the primary mechanism of development is biochemical or biophysical, it appears prudent to steer clear of all suspected causes of bubble generation, and certain types of exercise are certainly among them.

Light aerobic activities, like walking and swimming, mildly increase heart rate and redirect blood from organs to muscle and associated tissues. Before a dive, such exercise will not affect nitrogen uptake. After a dive, it would be expected to promote safe offgassing and inhibit bubble formation and expansion. In fact, some studies suggest light exercise decreases the incidence of DCS.

However, vigorous aerobic exercise, like hard running or strenuous hiking, produces pronounced changes. Markedly increased temperature, blood flow, and oxygen use within tissues immediately before a dive could result in an undesirably rapid uptake of nitrogen upon descent. After a dive, such exercise or an exhausting surface swim to the boat could contribute to a dangerously accelerated elimination rate.

A diver, especially one who fought heavy current,
should keep from getting chilled and maintain
slow, steady motion during the safety stop.

Some scuba venues, like Hawaii, invite arduous post-dive hiking to altitudes that can seriously compound the worries. Don't hike too soon after diving, and if trekking remotely near altitudes of 8,000 feet, follow DAN flying-afterdiving recommendations of waiting 12 or more hours after making a single no-decompression dive and 17 or more hours after making repetitive dives.

Stay Warm

Temperature and circulation alterations during a dive also have implications. Dr. Jolie Bookspan notes in Diving Physiology in Plain English that "Being uniformly cold throughout your dive seems to decrease decompression risk. . . . A diver starting a dive warm absorbs more nitrogen at depth than a cooler diver. If the warm diver then chills, common toward the end of a dive, eliminating the additional nitrogen gas burden slows, increasing risk."

Another effect of exercise relates to the rapid moving apart, and rubbing together, of joint, tendon, and other musculoskeletal surfaces; they are bathed in fluid that becomes turbulent when forcibly disturbed. Wrestling with cylinders and reentering the boat in full gear can generate seed bubbles that may serve as receptacles for nitrogen passing from the dissolved stage to the free gas phase upon ascent. While scientists are uncertain about their effect on DCS, it would be prudent to avoid or minimize activity stressful to joints.

Another worrisome effect of strenuous exercise is bubble creation in synovial fluid caused by the rapid moving apart, and rubbing together, of joint, tendon and other musculoskeletal surfaces. In fact, Dr. Michael R. Powell, a NASA research scientist, opines that there is no single causative factor greater than strenuous exercise shortly after a dive for increasing the risk of DCS.

While it is impossible to confidently attribute DCS to strenuous activity in other than a laboratory setting, there are anecdotal reports. For example, Fiona Watson, a medical professional in the U.K., told Undercurrent that in many years of scuba, including deep decompression dives, she had been bent only once, during the recovery of a heavy copper soup tureen that had to be wrestled with before being lifted to the surface. Upon reaching the boat, she pulled in a heavy shotline and unloaded gear and weights. Thirty minutes later, while handling her cylinders, an itch and skin mottling intensified in her arm and elbow, and she developed marked muscle/ joint discomfort. Being a long way from a recompression facility, she drank water and breathed 100 percent O2 for 3 hours. The skin manifestations soon disappeared, but the muscle/joint pain took seven days to resolve. Later discussions with chamber personnel confirmed that this almost certainly was a DCS hit.

She also relates the situation of a male buddy, also a serious diver with no history of DCS. He made an air dive of 34 minutes to 90 feet, then meandered back to 45 feet for most of the dive, and completed a three-minute safety stop. Upon exiting the water, he helped raise a heavy shotline. About 25 minutes later, he experienced continuous dizziness, vomiting, nausea, and incoordination. He was transferred to a chamber and required hyperbaric treatments for several days. He permanently gave up scuba diving.

How Long to Wait

DAN's Medical Center website suggests a two-hour delay after exercise as a minimum guideline for diving and considers four hours safer. Since vigorous postdive exercise almost surely is more pernicious than pre-dive activity, additional conservatism seems warranted. Some studies suggest that while the biggest increase in risk may occur within an hour or two of arduous exercise just before and just after a dive, risk likely remains somewhat elevated up to six hours.

Of course, the number and frequency of dives on any trip will bear on the degree of conservatism that would be prudent. For example, after 3-4 days of diving deep walls, you'll want to be more cautious than when doing only a single shallow dive and then returning home.

These estimates are consistent with Dr. Ern Campbell's (aka Scubadoc) suggestion: "If one were to put four restful hours between exercise and diving and six between diving and exercise, a diver should be in good shape in terms of absent bubbles."

However, regarding the postdive interval, don't take "restful" too literally. Sleeping immediately after a dive could slow nitrogen elimination to an unhealthy degree. Sensible amounts of light activity such as easy walking or warm water swimming, will promote nitrogen elimination.

Are there other exercise- DCS associations?

Dehydration and exerciseinduced pain are exercise-related factors that can prove problematic. Risk statistics consistently show a sizeable association between dehydration and susceptibility to DCS. Perspiration due to vigorous exercise, especially in hot weather, can further the fluid loss already inherent in scuba.

Given that joint pain is among the most common symptoms of DCS, injuries to joints and muscles provide fertile ground for confusion between DCS-related pain and exercise-induced discomfort. Avoid them, and the unnecessary chamber visits they may occasion.

The best advice is moderation. Stay well hydrated and warm. Avoid strenuous exercise of any type for 4 and 6 hours before and after diving, respectively, but remain mildly active between dives and for a while after the last dive.

Reduce anxiety and confusion about symptoms of DCS by knowing the location and characteristics of your pre-dive aches and pains, and be alert to changes in their nature or intensity.

-- DocVikingo

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