MICHELLEHAYWOOD
Cramping our style
Feeling the burn while finning ? Michelle Haywood digs into the science of muscle reflex and the central nervous system
For many divers , the winter break of 2019 / 2020 extended into the Covid break of 2020 and then back into winter 2020 / 2021 . As vaccine coverage improves and restrictions start to be lifted , then for some divers summer 2021 may be the end of a nearly two-year break . The term ‘ dive fit ’ gets bandied around quite a lot without necessarily explaining what that might entail . Equipment serviced and working ? Suit seals checked ? Your personal fitness ? Your state of mind ? Yep , it ’ s all of these .
Every year as the ‘ season ’ kicks off , I find it ’ s harder to carry more than one cylinder , but by the end of summer picking up two twin-sets is a doddle . Sadly I ’ ve never found the magic formula to maintain those muscles across winter . Pointlessly carrying cylinders around for just the sake of keeping a few muscles is a challenge that I ’ m not willing to take on .
For many divers , the early season dives are a chance to take it easy . Let ’ s face it , most divers don ’ t like working too hard underwater anyway . If you find yourself swimming too hard , you ’ ll probably be cursing the dive manager in your head . Exercise-related muscle cramps are common in the large muscles of the legs during or immediately after exercise . For many years , we ’ ve been told that dehydration , salt deficiency and accumulation of lactic acid were the driving causes , but actually there is little scientific evidence to support these connections . For dehydration to be a driving factor , you ’ d probably be displaying clinical signs of dehydration ; dizziness , tiredness , dry mouth , lips and eyes .
Instead , the cause of cramps may lie in the reflex nerves that control the muscle . There are two sensory receptors involved , muscle spindles and the Golgi tendon organ ( GTO ). The GTO senses changes in muscle tension . It lies in the tendonous area at the end of the muscle fibre . If the GTO is stimulated it sends a reflex signal via the spine and causes the muscle to relax . The muscle spindle is embedded in the muscle itself . The reverse situation occurs if the muscle spindle is stimulated and a muscle contraction occurs . Cramp occurs when the Central Nervous System ( CNS ) control of the reflex is lost . The GTO becomes inhibited and the muscle spindles become hyperactive . This leads to sustained activation of the muscle .
If we follow this theory through , then a muscle ’ s hyperexcitability is the basis of cramping and , therefore , stretching should counteract the cramp . And guess what ? We ’ ve know that for years . Stretches need to be held for 15-30 seconds or until the muscles relax . After the cramp has gone , then avoiding exercise for the next hour or so and applying heat will help . This allows the muscle and the CNS to recover .
What can be done to avoid cramps in the first place ? Well , the usual suggestions of hydration and salt in the diet probably aren ’ t going to help . Albeit , it ’ s hard to do a controlled trial on yourself ; hydrating one leg and not the other is impossible . Instead , we need to think about maintaining health reflex arcs . Poor flexibility caused by prolonged sitting , poor posture or inefficient biomechanics will make it more likely that the reflex malfunctions . Age is also a factor and divers who haven ’ t ever experienced cramp may do so as the years advance . Increased body weight and eccentric muscle contraction ( where the muscle lengthens as the load is greater than the force the muscle can produce ) are both factors .
Lots of publications suggest that the choice of fins for the diver may be the single biggest driver of cramps . Weak leg muscles needing a smaller , thinner , flexible fin ; athletic legs can drive wider , longer , stiffer blades . Fin manufacturers add in a number of features to improve performance , ribs , channels , vents and the material of the blade too . However , it ’ s more likely that repetitive finning motions are driving CNS fatigue and loss of control of the reflex . If you feel cramp starting , change your position , change your fin stroke and maybe try to just float for a bit and allow the CNS to reset . �
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