Mark Standhaft is a 23-year-old relatively new type 1 diabetic patient, who needed some assistance with his management of his diabetes with his cycling.

His diabetes is managed with Glargine 30 units at night and Novorapid between 22 and 26 units three times a day. Prior to the diagnosis of diabetes, as a junior, he was competing at international levels racing in Europe and he aspires to return to his previous high level of international racing, but currently he races at club level.

Mark’s exercise regime consists of almost daily intense cycling. On Monday he rests. On Tuesday’s he goes to work and in the evening he has a 2-hour race, this is usually about 6 o’clock in the evening. His blood glucose at the start of the race is typically 15, and falls down to 2 or 3 throughout the race. On Wednesday’s he goes to work and in the evening he trains for 2 hours. This consists of interal training with short bursts of high output training, followed by lower rates. This is to build up his lactate tolerance. On Thursday again he races for 2 hours in the evening and on Friday he trains for 2 hours in the evening much in the same way as Tuesdays. On Saturday mornings he trains for 4 hours starting at 10 o’clock in morning having had his breakfast at 8 o’clock in the morning and on Sunday’s he races again for 3-4 hours at about 10 o’clock having eaten his breakfast a 6 o’clock.
It is in these last 2 episodes that he finds it particularly difficult to control his blood glucose and in particular, he is finding that he has marked loss of performance during the training and has the greatest of difficulties, maintaining his blood glucose throughout the training period. Conversely after the exercise, he finds his blood glucose rises very rapidly.

As far as food is concerned, Mark did not measure the quantity of carbohydrate that he is eating, he is trying to lose weight and get his body fat down. He has 2-3 large bowls of cereals in the morning (estimated at least 100 gms of carbohydrate). He has a sandwich at lunchtime (about 90 gms), and then he has flapjacks several times throughout the day, which are approximately 30 gms. In the evening he has his main evening of again of rice, pasta or potatoes. Whilst racing he takes a glucose containing fluid and he drinks 500 mls, which is probably 30 gms of glucose during these training periods.

The problems that Mark is facing is that he has doesn’t know his total energy intake or requirements are. He needs a strategy for dealing with feeding, for rest days, training days and race days or strategies to deal with races in evening or in the morning. He is reacting to his blood glucose results rather than being proactive and his insulin regime may not be appropriate for different levels of physical activity on different days.

It is of particular note that Mark’s blood glucose falls during racing, that even though his blood glucose starts at 15 and that he takes regular carbohydrates throughout the racing, his blood glucose falls by more than 10 mls, leaving him at risk of hypoglycaemia. This is an extremely common feature of sub-maximal exercise in diabetic patients. Mark’s exercise really can be described in 2 types. His racing which would be typically at a VO2 of somewhere between 50-60%. In this exercise he is relying on muscle glycogen and blood glucose, which is sourced from the liver. However, his main fuel source would appropriately be free fatty acids and ketones bodies. One of the features of Mark’s situation is that his ability to mobilise fuel sources is reduced by excessively higher levels of insulin, hence his fatigability. He is therefore relying on glucose output from his liver to support his exercise, which is limited. During certain parts of Mark’s exercises however, his VO2 max will increase substantially. In this situation, his exercise will be limited by the fuel supply of glucose and also his ability to tolerate lactate.

Mark could use the following strategies deal with his problem. The first is to find out from either his own records or from his colleagues the total quantity of food that he needs to ingest in the day. This should then be divided up into appropriate feeding times and quantities so that we can then measure his carbohydrate intake accurately throughout the day and give his insulin doses related to that. One can estimate that Mark’s basal metabolic rate would be about 2,500 kilo calories and that approximately 1,000 kilo calories per hour with strenuous exercise, he needs his daily intake of somewhere between 4,500-5,000 calories a day. This assumes a total daily energy carbohydrate intake, if we assume 70% of his calorie intake, it should be as carbohydrate of between 700-800 gms of carbohydrate per day. Clearly the type of carbohydrate needs to be mixed in the course of the day, so that on normal working days when he is working in the evening, the carbohydrate should be given in complex forms with his breakfast and his lunch but swapped to rapidly absorbing low glycaemic index or when racing. A starting dose would be 60 gms per hour, but this may need to be increased to as much as 200 gms per hour depending on the intensity of the race. After racing, he should immediately have some further carbohydrate followed by a small dose of quick acting insulin prior to his evening meal for which he should give the further normal dose of insulin.

On days when he is racing in the morning, he should have his normal pre-race breakfast, with carbohydrate throughout the race, a post-meal snack with insulin and then his normal food. On days when he is resting he should have his normal food intake minus the extra carbohydrate intake associated with exercise.

Next we come to his insulin therapy:
Mark’s insulin therapy seems sensible at the moment; however, he needs a further small dose of insulin with snacks between breakfast and before racing in the afternoon (30 gems of carbohydrate with 6 units of Novorapid with each of these snacks). Insulin should not be taken sooner than 3 hours prior to exercise. However, on days when he is racing, cycling or training in the morning, his overnight insulin should be swapped from Glargine to Humulin I and the dose reduced by half. It is very important that he has little insulin in his system on those mornings as this will reduce his ability to mobilise free fatty acids and ketones bodies and may provoke in-race hypoglycaemia. He should however have his breakfast at least 3 hours before cycling in the morning and have half the normal insulin dose at that time, with the aim of starting the race with a blood glucose of somewhere between 10-14.