Cramp! A diver's Guide

One of the potential physiological effects of extended range, cold water and technical diving is the increased risk in the occurrence of muscular cramp. As diving evolves with the use of exotic gas blends and tekkies push ever deeper with extended deco and dive times, the need to be water-fit is more important than ever. Cramp is unpredictable, can be dangerously debilitating and if it hits at an inopportune moment could just be the trigger that sends a diver spiralling into the incident pit.

Although the exact cause of cramp is idiopathic there are some known triggers. These variable factors include poor physical fitness, reduced  flexibility, muscle fatigue, electrolyte imbalance and dehydration. Divers also have the additional predisposing considerations of cold water diving, new, restrictive or badly fitting kit and changes in body carbon dioxide levels. Most individuals have a susceptibility to a particular trigger. So to help minimise your risk of suffering from an attack, here is the definitive divers guide to cramp.

Physiology,  Muscles and Movement

Skeletal, cardiac and smooth are the three different muscle types found in our body. Of these types, skeletal makes up the largest percentage and is the type most susceptible to cramp. It is the only type that we have voluntary control over, through movement. Most muscles are capable of performing more than one type of movement and most movements require the use of more than one muscle. Movement works on a principle of leverage and is brought about by a combination of the muscle (providing the force), the bone (lever), the fulcrum or pivot (joint) and the load (resistance) which in diving is water.

All muscles attach via a tendon onto a bone, hence the term skeletal. Muscle mass usually constitutes between 40% and 50% of total body weight which in turn equates to strength. The prime function of healthy, strong muscle is to turn chemical energy into mechanical energy. This energy generates the force needed to perform work and produce movement. Muscles are always held in a state of permanent tension, providing postural support and resistance to gravitational pull, so they never fully relax. In order for one muscle to contract and make a movement, another muscle has to slacken to allow the motion. Muscles are therefore categorized into prime mover (agonist), oppositional mover (antagonist), assistor, fixator or synergist (refiners of movement) depending on what they are doing to bring about a specific action. Any muscle that spans or is connected to two joints will be more prone to injury and cramping. This is because these muscles are sometimes expected to perform more than one action simultaneously. They are known as biarticular muscles. It so happens that many of the larger groups of leg muscles used during a dive fit this profile such as the hamstrings, the quadriceps and the gastrocnemius (one of the calf muscles).

Monster Contractions

Cramps can generally be separated into four types and are classified by their causes and the muscles that are affected. These categories include dystonic,  contractures, tetany and true. True cramps are overwhelmingly the most prevalent form of cramp and the type we are most likely to encounter as a diver.

True cramp is an abnormal, involuntary, painful and sustained muscle spasm. It can be severe with spasmodic contractions affecting muscles singularly or as a group. Attacks can range from short lived twitches lasting for only a few seconds to prolonged, unremitting spasms of over 30 minutes. A cramp may involve only part of a muscle or the entire muscle and can recur numerous times before abating. It is linked to the hyperexcitability of the nerves that fire muscles. During an episode, the contracted tissue bulges outwards and becomes painful and unyielding. Localised inflammation can arise as the involved tissue fibres tear when an already tight muscle starts to cramp, shortening it further. The surrounding soft tissue responds protectively with additional spasm intended to minimize movement and stabilise the damaged tissue. This is why after a deep or particularly painful cramp, the area can feel tender and swollen for some days afterwards. The best way to relieve an attack once a muscle starts to involuntarily contract is to stretch it, along with massage and, if land bound, sometimes gentle heat. 

Heat cramps, a variation of true cramp, are associated with prolonged exercise coupled with excessive sweating. They happen retrospectively once the body has relaxed. These muscle spasms tend to be intermittent, short lived but excruciatingly painful. They affect muscles that were previously working the most intensively. This particular body response is associated with electrolyte imbalance, dehydration and intracellular fluid changes. Body temperature doesn’t necessarily have to increase for heat cramps to occur as it is fluid loss that is the key trigger. Even so, a diver is more likely to suffer while diving abroad in a hotter, humid climate or after overheating while cocooned in exposure suits when sweat loss is likely to be high. Heat cramps respond well to ice packs, applied over the spasm for a few minutes.

Contracture cramps are linked to a depletion of ATP (adenosine triphosphate) the energy carrying compound we all have. ATP reduction prevents the muscles from relaxing, leading to constant spasms. This is an uncommon form of cramp.

Dystonic cramp affects relaxed muscles that are not actually being used in a specific movement but work opposite the muscle group that is performing the action. This is associated with repetitive activities and is a protective reaction. It commonly affects the hands as in writers cramp and is uncommon in diving. 

Carbon Dioxide – A double edged sword

Carbon dioxide works against a diver in two main ways. Elevated levels can lead to CO2  toxicity (hypercapnia) and black out, one of the key considerations when diving on a rebreather. There is however another, lesser known side to carbon dioxide. Tetany is a particular form of cramp that can be brought on by hyperventilation when the tension of alveolar and arterial CO2 is lowered. This condition is known as hypocapnia. The physical manifestations are remarkably similar to hypoxia (oxygen toxicity) but tend to have a more gradual onset. Symptoms range from dizziness and tingling to muscle twitching, spasms and rigidity. Tetanic cramps will often affect the arms and legs but in severe cases the whole body. 

Tetany is more likely to influence freedivers who voluntarily hyperventilate but could also affect open-circuit divers suffering from stress or anxiety who involuntarily hyperventilate when rapid breathing sets in. It is in fact relatively easy to inadvertently lower body carbon dioxide levels. If the ‘in’ breath is shallower than the ‘out’ breath, and the breathing rate rapid enough, CO2 is blown off and after only a few breaths symptoms can present themselves. 

Mineral Heroes

A further known influence over cramp occurrence stems from mineral (electrolyte) depletion. Potassium (K), magnesium (Mg), calcium (Ca) and sodium (Na) levels are all important when it comes to muscle health. Potassium and sodium work together to aid nerve function and are crucial to body water balance and fluid regulation. Both can be affected by sweat loss and diuretic activity. Magnesium and calcium work together in aiding muscle contraction and nerve impulse transmission. All the electrolytes and their levels are interdependent in regard to muscle function. Their chemical closeness is depicted spectacularly by where they are placed within the Periodic Table. All four minerals sit together in a neat block, each one connected to each of the other three.









Of all the minerals, calcium is the most important when it comes to muscle action. Muscles are activated by nervous stimulation producing what is known as an ‘action potential’. The resulting contraction is called excitation-contraction coupling and relies upon the movement of calcium ions from the outer muscle membrane (sarcoplasmic reticulum), where it is stored, into the inner fibrous muscle tissue (sarcoplasm) where it is utilised. Muscle fatigue occurs when an inadequate release of calcium from the outer membrane results in a decline of calcium concentration within the inner muscle fibres. Add to this failing action potential the influence of insufficient oxygen, glycogen depletion and an increase in lactic acid (all of which further fatigue muscle) and you have a cramp recipe ready to cook.

Recommended daily allowance (RDA) for minerals and vitamins changes from time to time as nutritional research evolves, so if you plan to take nutritional extras, it is always a good idea to do so under professional guidance. Mineral supplementation would usually be around 500mg calcium and 300mg of magnesium daily with an upper safe daily therapeutic dose suggested as 1000mg for calcium and 800mg for magnesium. Potassium has an RDA of 2000mg with an upper safe therapeutic limit of 3000mg. Sodium is the one mineral found abundantly in our 21st Century diets. Even so, if you are subject to excessive sweat loss then a suggested dose of 1000mg daily is usually ample to maintain balance.

A mineral hero recipe that packs a punch and helps to stave off cramp attack includes a banana (potassium), tub of yoghurt (calcium) and a handful of brazil nuts (magnesium) with a sprinkle of salt. Wash this down with an isotonic drink of 50% water and 50% orange juice (electrolyte minerals, vitamin C) an hour or so before diving and you should have happy, sappy  muscles.

Feeling the Pinch

Any item of kit that impairs or restricts your circulation will massively stress the surrounding muscle group and associated soft tissue. Of all the many articles in a divers kit bag, the fin is probably the biggest culprit in contributing to the onset of cramp. If this is the situation, it is usually because the fins don’t fit properly. With this in mind it pays to spend time choosing the right pair. If a fin is broken down into its component parts, the blade, strap & buckle and the foot pocket, it becomes easier to work out what will suit you best. The following discussion assumes that most tekkies use open-heeled fins.

The foot pocket should be flexible on top, firm underneath, soft edged and fit comfortably without squeezing, squashing or pinching. There should be room to wiggle your toes. If it is too tight or too loose you will almost definitely suffer calf cramps. The under part of the pocket should be long enough to support the heel of the foot. If it falls short and cuts into the arch, the foot itself is likely to cramp. As drysuit boots tend to be bulkier than wetsuit booties you need to try the fins on with both.

The straps should be adjustable with quick release buckles that can be tightened or loosened underwater if need be. Adjustable straps allow for use with a variety of different boots making it possible to extend the size of the foot pocket (keep in mind the need to support the sole of the foot). The straps should be just tight enough to hold the fin in place. If they are pulled too tight, the foot is likely to cramp.

The blades should ideally be chosen to suit your build, leg strength and the type of diving you are under taking. For example, if a diver has weak leg muscles then a smaller, thinner and more flexible fin would be a better choice. For fit, leg strong aquanauts a larger, wider and stiffer blade that generates greater power might be preferable. Most blade designs incorporate hydrodynamic vents, channels and ribs to improve in-water performance and reduce energy sapping fin wobble. Blade snap (how quickly it returns to normal after flexing) is also important. The quicker and more forceful the return, the better for your muscles as the fin should be ready in neutral for the next kick cycle.

Finally the overall weight of the fin will have an impact on how hard your muscles have to work to propel you through the water. Weight will be determined by the constituent elements used in design. Most fins have a composite construction with a variety of materials utilised including rubber, neoprene (heavy weight), graphite (strength), silicone, carbon fibre (flexibility), fibreglass (stiffness) and thermoplastics (light weight).

Consideration should also be given to other items in a divers kit bag. Overly tight exposure suits and restrictive hoods can compromise circulation. In fact any kit that imposes a constraint and hinders movement can lead to the onset of cramp. Furthermore, equipment that interferes in any way with circulation will reduce the efficiency of off-gassing. Inadequate oxygen reaching nitrogen saturated tissues will potentially increase the risk of a DCI hit. New kit can sometimes bring about a change in the way we move in the water. Even a slight alteration in attitude and style will influence muscle workload, potentially involving a muscle that was previously not used. If this is the case, then until that muscle becomes water-fit it will fatigue more quickly and therefore be prone to cramp attack.

Don’t Cramp your Style

Many divers adopt a particular pattern of repetitive movements during their dive which overuse specific muscle groups, depleting their glycogen reserves and loading them with lactic acid. Such movements will be governed by finning style, kick frequency, attitude in the water, kit configuration, specific tasks and so on.  During strenuous, repetitive or sustained exercise, lactic acid is produced faster than the body can repay the oxygen debt needed to remove it. The acidic build up reduces energy production and slows movement as muscle fatigue sets in. This can happen with increased work load for example, when a diver is fighting a current head-on.  It is at this point during exercise that cramp is most likely to hit.

One of the best ways to prevent muscle overuse in diving is to vary your finning style during a dive. Cave and wreck divers have already adapted to using a wider range of kicks to account for diving in overhead environments and narrow spaces, the emphasis being to avoid silt-outs. Flutter, modified flutter, frog, modified frog and shuffle kicks are all used throughout a dive along with hand pulls and ceiling push-offs, switching between styles as the topography dictates. As well as these techniques there are scissors, dolphin and backward kicks, sculling, pivot turns and flaring to help break the monotony of the flutter kick. In open water we don’t necessarily need such a variety of finning techniques but it helps spread the work load and your muscles will thank you for it. If we take three of these styles and look at the muscles involved it becomes easier to demonstrate this.

The flutter kick is the most commonly used finning technique and the one we all learn during our first open-water course. The kick comes from the hip, legs are extended with a strong downward thigh thrust propelling the diver forwards. The main muscle groups involved with this action are the hip flexors (iliacus and psoas) and the quadriceps (front of thigh) and the hip extensors (hamstrings) for the return effort.

The modified flutter is used in cave and cavern diving to reduce the likelihood of a silt-out. Rather than kicking from the thigh the thrust comes only from the knee while the thigh remains stationary and horizontal. The prime muscles involved in producing the knee bend will therefore be the hamstrings (back of thigh), gastrocnemius (calf) and soleus (smaller calf muscle involved in ankle action) followed by the quadriceps to straighten the knee. This style won’t propel you as fast through the water but will rest tired thigh muscles by altering the work load expectation on them. If you are diving in calm, current-free water it is an easy enough style to adopt. It’s also worth using on dives that have a silty bottom composition, especially if you are using the same point for entry and exit and will be retracing your route.

The frog kick uses a completely different set of muscles and is the ideal companion to the flutter kick. It is similar to the breaststroke style kick. Legs move from being extended straight along the midline of the body, knees then flex to assist a leg spread as wide apart as is comfortably possible and feet are rotated so that the bottom of the fins face each other. The power comes from the action of forcing the legs closed again and displacing the water between the fin blades. Even though the quadriceps are still used in this movement they are no longer the prime movers but become assistors and the emphasis changes instead to the adductors (inside thigh), abductors (outside thigh), gluteals (buttocks) and the hip rotators.

This is not a recommended style of kicking however if you suffer from either a groin injury or lower back stress  (it can shorten the deep muscles within the sacro-iliac joint leading to sciatic nerve compression).

Interestingly, in swimming, the breaststroke kick produces about 70% more propulsion than any other kick stroke. It is upper body strength that dictates speed which is why crawl is the fastest stroke. Female divers adapt particularly well to the frog kick as their pelvis is wider and more flexible than males. 

Thermal Considerations

When we look at temperature regulation the most crucial area physiologically is our central core. This includes all the vital organs, spine and central nervous system. The core is prioritised naturally to keep it a constant 37° C. This means that the temperature of the extremities, skin, adipose and connective tissue is less important and can therefore be allowed to fluctuate to protect the inner core.

Cold environments are known to increase the risk of cramp. This happens as a result of a simultaneous increase in muscle tension while circulation is reduced (vasoconstriction). Body heat transfers outwards as skin temperature unifies with the ambient colder temperature. Exposure suits only delay the length of time this will take. As soon as we have chilled sufficiently we start to shiver. In fact it is our muscles that take the brunt and their reactionary shivering is an attempt to increase body heat by rapidly and repeatedly shaking, using up vital energy supplies. The increased muscle activity can produce up to 18 times more heat than that provided by the same muscles during rest. Heat generated by shivering can easily exceed that produced during moderate exercise. The resultant thermal stress however adds yet a further negative to our already challenged leg muscles making cramp a likely outcome.

Water Fitness

In all sports, athletes are more prone to cramp at the start of season or during the preseason run-up when their muscles lack conditioning and are easily fatigued. Cramp tends to strike towards the end of a prolonged spell of exercise when muscle glycogen levels have been depleted.

Serious athletes follow the principle of ‘positive adaptation’ (known as the training effect) to prepare themselves for the specifics of their particular sport. In doing so, the athlete reduces the risk of injury and cramp by becoming fitter. To achieve a training effect, the body needs to be exposed to exertion and effort that is greater than that encountered during the normal activities of daily life. Fitness is assessed by looking at the key components called the 5 ‘S’s which are suppleness, strength, stamina, skill and speed. Speed is the least important component when looking at a divers fitness. The other four aspects however are of equal relevance.

Water is 800 times denser than air which means that our muscles work that much harder against the increased resistance. If you add a strong head-on current, kit bulk and ankle weights to the equation, it is easy to see why being water-fit is so important to a diver. The weightlessness of being in innerspace doesn’t detract from the fact that during a dive there will be major physiological stress on muscle tissue, whether or not you are aware of it.

Technical diving is in its own way an endurance sport, purely from the point of view that the diver is expecting their body to produce a sustained performance whilst coping with the additional considerations of heavy and complex kit, increased atmospheric pressure and thermal stress. With this in mind, personal fitness should have a high priority.

To realize positive adaptation a diver needs to consider the type of diving being undertaken. A performance improving training schedule should be planned taking into account the intensity, duration and frequency of the diving and should mimic the actions that will be encountered both above and below the water. As an example: strength training using weights, cardiovascular workouts (including swimming) to improve stamina, stretching routines and yoga for flexibility and finally pool training to practice propulsion techniques and skills.

In sports medicine there is an aspect of fitness known as proprioception. This is the science behind body awareness, balance and co-ordination. Proprioceptive training prepares muscles for the unique, unconscious actions involved in a particular sport. This fine tuning is done with the help of propriceptors which are specialised sensory nerve endings. These sensory nerves monitor the internal changes of the musculo-skeletal system that are brought about by movement and muscle activity. So, how does this help in the battle against cramp? Simply by improving one’s understanding of how your body works, how it moves, what combination of movements work best for you, most efficient attitude in the water, where you are in relation to objects around you, sensitivity to kit and so on. A heightened awareness enables you to pre-empt physical limits and avoid some of the cramp triggers by taking preventative action.

Diving revolves around movement in a three dimensional plane and ideally, proprioceptive training should be carried out in the same liquid environment. This is where pool work really comes into it’s own. A diver with excellent proprioceptive skills would for example be able to access any item or part of their kit accurately and immediately, without fumbling. They would also be able to perform most skills with their eyes shut. They would be aware always of their proximity to other divers, distance of their fins from the reef and so on.  This all adds up to making a diver more efficient which in turn reduces the stress on muscles and soft tissue and therefore minimises the risk of cramp.


As a preventative measure against cramp and injury, stretching is one of the most effective tools available. Stretching provides a number of other useful functions such as reducing post exercise muscle soreness, improving neuromuscular function and increasing soft tissue flexibility. Muscles that are stretched are encouraged to relax and remain elongated even during exercise. This is why it is good to stretch before exercise.

Muscle fibres elongate via a number of mechanical processes that stretch the elastin within the muscle. Stretching techniques include static, passive, active, ballistic, assisted, dynamic and also proprioceptive. The type most suitable and safe for a diver (immediately pre and post diving) are static. These are the normal type stretches that most active people are familiar with. Effective static stretching involves moving one end of the muscle as far as is comfortably possible away from the other end. Static stretches are generally split into two types depending on what you are trying to achieve. Maintenance holds of 6 – 10 seconds will temporarily elongate muscle fibres. Developmental holds last as long as 20 – 30 seconds and will semi-permanently alter the length of muscle fibres. By introducing a customised stretch routine into pre and post dive preparations, a diver can significantly reduce the likelihood of cramp episodes and soft tissue injury.

The End of the Day

As with most undesirable situations, prevention is better than cure. Look after your muscles and they will look after you. The human body is a fantastically complex machine. Peak performance requires a fundamental understanding of needs and the ability to provide them. We are designed to move, so to ensure that you gain the maximum from your machine, put the maximum into it and as with any good investment, you’ll reap the rewards.

"Life yields only to the conqueror. Never accept what can be gained by giving in. You will be living off stolen goods, and your muscles will atrophy." – Dag Hammarskjöld (1905–61), Swedish statesman

Photos by Mark Harris