Physical Exercise Before, During & After a Dive

Researches have recently uncovered facts regarding the relationship of exercise with diving. Dr De Kock explains this controversial subject in details.

As potential risk factor for decompression illness (DCI), physical exercise remains subject to controversy. Not only is the optimal interval between the exercise and diving uncertain, but the type and intensity of the exercise itself are also cause for concern. Former general recommendations have been based on expert opinion, some anecdotes and perceived biomechanical and biochemical processes. Moreover, with DCI itself being so unpredictable within the conservative exposures associated with recreational diving, the independent influence of exercise is difficult to determine. Is it exacerbating or mitigating? We still do not know for sure, but some evidence has emerged that is able to guide the way. Recently, researchers have uncovered some very interesting facts regarding the relationship of exercise with diving. This research may better equip today’s recreational diver to plan their interval between the dive and the treadmill with greater confidence.

When it comes to exercise, there are essentially two potential interest groups. Firstly, there are the “fitness fanatics” who want to exercise whenever and wherever they can: before, during, after and in-between dives. Their interest lies either in actively lowering or at least not accidently provoking DCI. Secondly, there are those divers who want to stay in shape or perhaps combine their diving vacations with other sports or physical activities. Their interest is simply to avoid increasing the risk of developing DCI. With these two groups in mind, the following general recommendations have emerged from a variety of workshops, discussions and reviews of recent evidence and appear central in the ongoing debate [1-6]:

• General: Physical fitness is regarded as an essential requirement for the recreational diver to ensure the safety and enjoyment of the activity as well as to assist in protecting against DCI.
• Type of exercise: Moderate aerobic exercise that does not involve heavy straining of the muscles and joints is preferred; rapid movement (high cadence) of limbs should be avoided.
• Exercise before and after diving: In general, the consensus amongst researchers is that exercise should be avoided within four to six hours before and after diving. Previously, this was set at 24 hours which was impractical.
• Exercise during diving: The objective is to minimise gas uptake and optimise outgassing under conditions least likely to precipitate bubble formation. With this in mind, minimum exercise should be performed during the on-gassing period of a dive (that is during descent and bottom time). Mild, non-strenuous exercise (moving limbs and swimming easily) should be maintained during the off-gassing period of the dive (that is during ascent and at the safety stop). However, it is very important to take care once back on the surface to avoid dragging oneself up ladders and to minimise excessive strain on limbs and joints by removing heavy dive equipment whenever possible. Rather lighten the load by passing dive gear from the water to the attendant before making the exit. Then relax for as long as possible before dissembling, carrying and cleaning your equipment. 
• Exercise between dives: Stay warm and maintain low-grade activity in between and after dives. This will facilitate ongoing gas elimination without provoking bubble-formation. Sleeping directly after a dive is not recommended as limb circulation may be impaired and if symptoms arise, they may not be recognised promptly.  

In addition to these general principles, the outcome of several studies is providing some additional refinement. Between 2001 and 2004, a series of animal studies in Norway showed that rats exercising 24 hours prior to diving had fewer venous bubbles – using ultrasound [7, 8]. Although bubble grades do not correspond directly to the incidence of DCI, they are an accepted marker of decompression stress and can serve as a basis of comparison between more or less conservative dive profiles. Exercise is only part of the story, of course, but these discoveries have been important in identifying the effect of exercise on blood vessel function which also has several implications relevant to cardiovascular research.

In 2004, the same Norwegian group determined that their findings in rats also applied to humans [9]: The benefits of 40 minutes of intermittent, strenuous exercise on a treadmill, done 24 hours before an 18 m, 80 minute chamber dive resulted in a significant reduction of venous gas bubbles in the heart. With that, the race for the optimal interval between exercise and diving was on.

So, in 2005 a study of navy divers examined the effects of 45 minutes of exercise two hours before diving [10]. Using a slightly different combination of exercise and a 30 m dive for 30 minutes, these researchers also found a significant reduction in bubble grades. The researchers concluded that exercise as little as two hours before a dive might be expected to reduce the number of bubbles and, with it, hopefully reduce the incidence of DCI.
Then a group of French researchers truly pushed the limits of exercise before diving when they asked a study group of divers to exercise one hour before a dive and then observed their bubble counts upon exiting the water [11]. Again, the researchers found a significant reduction in bubble grades and numbers.

In 2006, a group of divers performed 10 minutes of exercise after open ocean dives of 30 m for 30 minutes [12]. Doppler ultrasound commenced 20 minutes after surfacing, during cycling and immediately after termination of exercise. Somewhat surprisingly, this study found that even post-dive physical exercise significantly reduced bubble formation. The researchers mentioned in their conclusion that this result was obtained in very well-trained (physically fit) navy divers and that additional findings (i.e. further extensive research) would be needed before conclusions could be extrapolated to “normal” recreational divers. We echo their precautionary notes.

Although these research findings are encouraging, it will take larger scale studies on the wider diving populations before the recommendations can be applied as standard practice. Research subjects used in these trials were clearly not representative of the average recreational diver. Moreover, experimental conditions demanded on-site medical support which is not the case for most recreational dive sites. When it comes to diving, fortune tends to favour the conservative.

Then, having said all this, surely a dive trip is meant to be relaxing! So, by all means, maintain the rigorous exercise programme prior to the dive trip. But until the safety of ultra-short periods between exercise and diving has been confirmed, waiting at least four hours after a dive (based on the known peak appearance of venous gas bubbles after diving) would be a bare minimum.

To summarise, I give you the words of Zeljko Dujic from his article Exercise, Endothelium and Diving Physiology [13]: “Based on the abovementioned findings, it seems that high-intensity, pre-dive exercise and moderate exercise performed during decompression stops would appear to be a wise prescription for reducing the number of venous gas bubbles after air dives. However, before these procedures can be widely adopted as a predictable safeguard against DCS, we need further standardisation related to the exercise’s duration and intensity.”
So, get out your running shorts, fill up your water bottles and head out into the fresh air to ensure that you are perfectly pre-conditioned before your next dive trip!