Dive Fitness and Health
Diving Is a Physical Activity
Scuba diving appears deceptively passive. Photographs show divers drifting weightlessly over coral, and the activity requires no obvious athleticism. But appearances mislead. Donning a full scuba kit — wetsuit or drysuit, BCD, cylinder, weight belt — adds 20–30 kilograms to your body. Walking to the entry point, gearing up on a rolling boat, or navigating a shore entry through surge requires cardiovascular effort and physical coordination. Underwater, a stiff current demands sustained exertion. Towing a fatigued buddy to the surface is a physically demanding emergency procedure.
More fundamentally, diving exposes the body to physiological stresses that have specific medical implications. Increased ambient pressure affects every gas in the body. Breathing under pressure increases the work of breathing. Immersion in cold water stresses the cardiovascular system. Underwater exertion increases gas consumption and nitrogen loading simultaneously. The medical requirements for diving exist because these stresses interact with pre-existing conditions in ways that can be dangerous.
The Medical Questionnaire and When to See a Doctor
Every reputable PADI or SSI dive centre will ask new divers to complete a medical screening questionnaire before issuing certification or equipment. This is not bureaucratic box-ticking — it is the filter that identifies conditions that require a physician's sign-off before diving is safe.
The conditions that automatically require physician evaluation include: any history of cardiac disease or surgery, asthma or chronic obstructive pulmonary disease, diabetes managed with insulin or oral medication, epilepsy, significant ear or sinus problems, psychiatric conditions for which medication is taken, and a body mass index above a threshold associated with significantly elevated cardiovascular risk.
Asthma deserves specific mention because it is common and because the guidance has evolved. Historically, any asthma diagnosis was considered an absolute contraindication to diving. Current guidance from the UK Sports Diving Medical Committee and similar bodies takes a more nuanced position: well-controlled mild asthma with a normal forced expiratory volume and no exercise-induced symptoms may be compatible with diving, assessed case by case by a diving medicine physician. The concern is bronchospasm triggered by cold, dry gas, which could cause air trapping and pulmonary barotrauma during ascent.
Diabetes requires careful management on diving days. Hypoglycaemia (low blood sugar) underwater is a life-threatening emergency. Guidelines from Divers Alert Network and the UK diving medical community allow controlled type 2 diabetes — and, under specific protocols, type 1 diabetes — in divers who can demonstrate stable management, test blood glucose reliably before and after dives, and dive with a fully briefed buddy. Dives should be shallow and conservative, and pre-dive blood sugar targets are higher than for day-to-day management to provide a buffer against exertion-related drops.
Ear and Sinus Health
The ears are the most commonly injured organs in diving. Middle-ear barotrauma from failed equalisation is painful and, in severe cases, can rupture the eardrum. Chronic ear problems — recurring ear infections, surgically implanted ear tubes, perforated eardrums, or previous ear surgery — require medical assessment before diving.
A key point that many recreational divers miss: diving with any upper respiratory tract infection or congestion is a poor decision. Congestion blocks the Eustachian tube, making equalisation difficult or impossible. Attempting to force equalisation against resistance can reverse-squeeze on ascent — trapped air expanding in the middle ear causes intense pain and potential rupture. The standard advice is: if you cannot breathe freely through your nose and equalise normally, do not dive.
The sinus cavities are subject to similar squeeze on descent and reverse-squeeze on ascent. Chronic sinusitis, nasal polyps, or the residual congestion of a fading cold can all cause sinus squeeze — felt as a sharp pain or pressure sensation behind the eyes or in the cheekbones during descent.
Cardiovascular Fitness
The diving medical community broadly agrees that the most important fitness factor for divers is cardiovascular reserve — the ability to sustain aerobic work when the situation demands it. A physically fit diver who encounters a current, has to swim against surge to reach an exit point, or needs to assist a panicking buddy, has a cardiovascular response available. A deconditioned diver in the same situation may reach anaerobic threshold rapidly, causing rapid gas consumption, elevated heart rate, anxiety spiral, and potentially a cardiac event in susceptible individuals.
Sudden cardiac death in divers is disproportionately associated with male divers over 45 who are not regularly active. Exercise tolerance testing as part of diving medicals for this demographic can identify individuals with reduced cardiac reserve or ischaemic changes that the questionnaire cannot detect. Several national diving medical associations recommend stress testing for divers over 45 who are not otherwise regularly exercising at moderate intensity.
The practical target for maintaining dive fitness is straightforward: any regular aerobic activity — swimming, cycling, running, rowing — that keeps resting heart rate in a healthy range and allows sustained exercise at moderate intensity. Underwater swimming and freediving breath-holds are excellent supplementary training.
Staying Dive-Fit Between Trips
The deconditioning between annual dive trips is a genuine health consideration. A diver who exercises regularly throughout the year and dives a week once a year is in a different position from a diver who is sedentary between trips. For the latter, the physical demands of the first diving day — multiple kit-up sequences, entries from a rolling boat, exertion against current — represent a significant cardiovascular load compared with their baseline daily activity level.
Building dive-specific fitness in the weeks before a trip is sound preparation: cardiovascular work to build aerobic capacity, and pool diving to refresh buoyancy and equipment handling skills. Some diving operators, particularly for remote liveaboard trips where medical support is limited, are now asking for a recent dive fitness declaration as part of trip booking.
Beyond aerobic fitness, core strength affects trim and buoyancy control. A diver with poor core stability has difficulty maintaining a horizontal trim and compensates with more finning, which increases gas consumption and bottom disturbance. Exercises targeting the deep stabiliser muscles of the trunk improve underwater posture in ways that are directly visible in dive performance.
Open the map to find dive sites for your next trip, and arrive at the water having done the preparation that makes every dive more comfortable and more safe.