and this occurred with a much lower release of insulin

(30%) from the pancreas. This suggests that the skeletal muscle, as 90% of all insulin mediated glucose uptake occurs here, has become much more insulin sensitive following HIT (Figure 2). In a separate study looking at HIT in overweight/ obese men, it was shown that following the same exercise protocol insulin sensitivity was greatly increased along with a significant improvement in endurance capacity (6). There was also a change in fuel utilisation at rest, with greater fat oxidation and lower carbohydrate oxidation in the fasted state. There was also a significant reduction in systolic blood pressure. Others have also reported a cardioprotective effect of a HIT programme in patients with coronary artery disease. If this type of finding could be repeated in patients with type 2 diabetes then the implications for disease management are massive. Much of the secondary complications associated with type 2 diabetes are thought to be due to either hyperglycaemia or hyperinsulinaemia following a meal.

Moving toward a useable training paradigm Despite the obvious benefits of HIT, such as time efficiency, there is a need to move towards a more useable training paradigm. A large majority of the research looking at both performance and health effects of HIT has used the standard Wingate sprint protocol. In recent studies there has been an attempt to move away from the 30-second protocol discussed above. The first published study has used a lower intensity of sprint at 100% of VO2 max but with more sprints and of a longer duration (7), and it demonstrated similar changes in oxidative capacity in skeletal muscle compared with the original 30-second sprint protocol. However, we believe that glycogen turnover is the major regulator for the magnitude of change following HIT and we know that the same glycogen utilisation could be generated with a much shorter sprint duration. In two studies that we have carried out we have demonstrated similar improvements of 15% in cycling performance in sub-elite triathletes using 10 x 6-second sprints with one minute of recovery between sprints per session, and similar improvements in insulin sensitivity (20%) in male participants using 2 x 15-second sprints with four minutes of recovery per session. Both of these protocols result in an overall decrease in exercise session time to 10 minutes, which represents a much lower training time than current exercise recommendations or other HIT training protocols. However all of these protocols require access to specialised ergometers which are not widely available. In response to this limitation we have been looking to see whether we can adapt the HIT protocol from cycling to running. Initial results show that a training protocol utilising 4 x 30-second uphill sprints (hill slope 1:10) three times per week over two weeks significantly improves aerobic performance in a group of young male rugby players. The second video demonstrates the uphill sprint and you can see the loss of speed/power over the 30 seconds, and this is similar to that seen in the cycle sprints. This suggests that we can indeed move away from cycle ergometers where appropriate but much more work is required to define the ideal HIT running protocol.

Conclusions and perspective For sports medicine I believe that HIT offers a unique training

18

A

120 P = 0.008

80

40 pre-training B 800 post-training

P = 0.001 600

40 pre-training C 5000 post-training

3000

P = 0.005

1000 pre-training post-training

Figure 2: Change in insulin sensitivity (A), blood glucose (B) and insulin (C) following 2 weeks of HIT in sedentary young men (5).

paradigm that can be utilised in injury rehabilitation. For an injured athlete there is a dramatic loss of endurance capacity and HIT could be employed to enable a much more rapid return to full fitness. Additionally, when performed on a cycle ergometer the impact of the exercise on the joints is minimal allowing the athlete to increase his training load faster. In conclusion, we can confidently say that HIT is a time-efficient training protocol that rapidly improves endurance performance in sub-elite athletes and improves insulin sensitivity in sedentary individuals.

*UK physical activity guidelines, Dept. of Health, UK http://bit.ly/r7KxXP; Guidelines for exercise, American Diabetes Association, USA http://bit.ly/uiXv6q

References 1. Burgomaster KA, Hughes SC, Heigenhauser GJ et al. Six sessions

The REPs Journal 2012;24(May):14-19

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