Manhattan Island Swim

Andy kept a food diary for the week leading into the race, and notably his carbohydrate intake was slightly below the 8-12g per kg of bodyweight recommended in the literature, averaging ~6g/kg for the two days prior. Increasing this slightly would optimise his stored glycogen levels and ensure he’s starting fully topped off. All of Andy’s swim nutrition came in liquid form, passed to him every 20 minutes from a support boat/kayaker. Having honed his skill of being able to drink between 200 - 300ml in less than a second (well-practised at university 😂), Andy also discovered during his North Channel Swim that when he gets cold there’s nothing he craves more than a warm drink to boost his morale and thermal comfort, as if to maintain his core temperature. There is, however, no scientific evidence to support this, as highlighted by a 2014 review of nutrition considerations for open-water swimming. However, it’s known that regular carbohydrate feeds will help maintain metabolic heat production, so it’s fair to assume that ingesting warm feeds can boost this, with the main effect being the enhancement of thermal comfort and psychological resilience. Andy’s crew managed this by mixing his carb drinks with 50% hot/cold water, which gave a psychological boost without burning his mouth.

Since all of Andy’s nutrition came in liquid form to make it easier to consume whilst swimming, it was hard to maintain a high concentration of electrolytes, and he averaged a relative sodium concentration that was quite low. When swimming in cold water, Andy knows that cold-induced diuresis is very common, where the body preserves heat by constricting extremity blood flow, forcing more fluid around central organs, triggering increased urine production as the body attempts to remove the ‘excess’ fluids it detects. Thankfully, with a liquid-based nutrition strategy, containing a small amount of electrolytes, Andy mitigates this well. He didn’t experience any dehydration-related symptoms during this swim, nor has he in previous swims when executing a similar strategy. It’s also likely that his sweat losses were low during this cold water, non-wetsuit swim, so he was likely meeting his sweat and electrolyte requirements sufficiently. Getting a Sweat Test would help optimise his intake, and allow a bit more detailed planning of his sodium intake.

Because this swim began in the middle of the night (2am!) Andy used a 100mg caffeine tablet plus the small amount of caffeine found in cola (~10mg/100ml) to give him a boost during the swim. As we learned from the first edition of our ‘Sports Science Unwrapped’ newsletter, a 2021 study reported that caffeine ingested in tablet form is actually absorbed and metabolised slower than other methods like dissolvable strips or caffeine gum. We’re not suggesting Andy tries to chew gum whilst swimming, but if he’s looking for a quick boost, perhaps some dissolvable strips could be something to experiment with, particularly during nighttime swims. The small amounts of caffeine from the cola every ~60 minutes will likely have maintained Andy’s circulating levels, but he will experience a larger benefit from a slightly higher dose. Aiming for the scientific guidelines of 3-6 mg/kg, so the stimulant can maximally for a race of this duration and intensity, will ensure he’s maximising the benefits.