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As fat burning is more likely to occur in the latter stages of the session, you should keep working at the correct intensity right throughout the 20 minutes. Towards the end of the 20-minute session your legs should be feeling slightly tired. After 20 minutes of interval sprinting, however, you should feel energised rather than exhausted.

It is important to perform the 4-minute cool-down so that the heart rate can return to lower levels before you get off the bike. A pedal rate and resistance lower than your warm-up – for example, 50 revolutions per minute at 0.5kg – should see your heart rate go below 100 beats per minute by the end of the cool-down. If your heart rate does not decrease quickly, then change your maximum pedal rate and resistance to 50 revolutions per minute at 0.25kg. Jumping off the bike immediately after sprinting is unadvisable, as it may cause blood pooling and fainting.

What is the best time of day to do interval sprinting?

The best time of day for interval sprinting is early in the morning, before breakfast. If you can do it without eating any food, we believe it will result in increased fat burning. If you can only exercise at lunchtime, try to stop eating for 2–3 hours before exercise and drink only water or green tea for as long as possible before your session. Exercising at night is probably the second-best option, as long as you can ingest your evening meal at least 2 hours before your session. For example, eating at 5 pm and exercising at 7 pm will give time for the insulin in your blood to subside.

Remember, insulin is elevated after eating sugar and protein and encourages fat storage rather than fat burning, so try to drink only water or green tea for as long as possible after exercise. Ingestion of sugar or protein before or after exercise will immediately result in an increase in blood insulin levels that will impede fat burning. The advantage of exercising at night is that you can avoid eating for at least 8 hours after exercising because you are asleep, which will allow the body to burn more fat, assuming you only drink water or green tea after exercise.

Music for interval sprinting

Performing interval sprinting to music makes it much more enjoyable, and while interval sprinting can be performed without music, attempting to time each sprint and recovery session tends to make the experience tedious. Music specifically developed for interval sprinting called LifeSprints is available on iTunes.

Methods of interval sprinting

There are a number of different methods for performing interval sprinting, including the following:

Sprint cycling

Cycling on a stationary bike is probably the optimal form of interval sprinting, as it is non-weight-bearing and thus less stressful on ankles, knees and hips. Most research examining the effects of interval sprinting has used the stationary bike, and there are a number of unique aspects of the stationary bike that other forms of exercise do not possess. For instance, the bike allows people to complete a significant amount of sprinting without getting exhausted. If a person uses the 8-second/12-second protocol and cycles at a pedal rate of 125 revolutions per minute during sprinting, then they would have sprinted 6.0 kilometres during the 20 minutes of exercise. If their rate was 85 revolutions per minute during each rest period, they would have pedalled an additional 6.1 kilometres, making a total cycling distance of 12.1 kilometres in a 20-minute session. The 8-second sprint protocol involves 60 sprints, resulting in a total of 1006 pedal revolutions for 8 minutes of sprinting during the 20-minute session. Thus, the optimal interval sprinting protocol would be to sprint 6 kilometres of distance using about 1000 pedal revolutions.

Table 6 (below) shows the pedal rates and distance cycled for low, moderate and hard interval sprinting cycle workouts.

These 1000 pedal revolutions place significant overload on the major leg muscles, such as the hamstrings, quadriceps and gastrocnemius. This stress placed on the legs is the likely explanation for the significant increase in muscle mass that we found in our 3 studies (see Table 4). Women increased their leg muscle mass by 0.2kg whereas men increased theirs by 0.5kg.

However, in all 3 studies the biggest increase in muscle mass was found in the core muscle area, which includes the rectus abdominis, external and internal obliques, and transverse abdominis. These muscles are isometrically contracted during sprinting to provide a platform from which to turn over the legs quickly. Isometric muscle contraction occurs when a muscle is contracted but does not change its length. In our 3 studies, both women and men had significant increases in these core muscles, with 0.4kg for the women and 0.7kg for the men. This increase in muscle mass after cycle interval sprinting is very important because, as mentioned earlier, it has been estimated that for each 1kg increase in muscle mass there’s an increase of daily energy burning of about 21 calories. If this muscle mass increase was maintained for 1 year, it would likely increase energy expenditure by about 7665 kilocalories, which would be equal to burning about 1kg of fat.

The workout that the leg muscles receive is likely to be the major reason why all studies that have examined cycle interval sprinting and glucose metabolism have shown that it reduces insulin resistance. This finding has major implications for the prevention of type 2 diabetes, which has been shown to be a disease of the legs and liver.

Table 6. Example pedal rates and distance cycled for a 8-second sprint/12-second recovery protocol for 20 minutes at light, moderate and hard exercise intensities (rpm = revolutions per minute).

Sprint rowing

Rowing on a stationary rowing machine is a good form of interval sprinting exercise. This exercise is also non-weight-bearing but involves more muscles than cycling, as it uses the upper body. As the limbs do not move as quickly as in cycling, however, it is not clear how sprint rowing will affect belly fat. Young adults performing interval sprint rowing in our laboratory have easily got their heart rates up to similar levels as those generated on the stationary bike, so it is likely that sprint rowing induces significant elevations in catecholamines. Studies measuring the catecholamine response to sprint rowing, however, need to be performed.

Sprint walking

Sprint walking can utilise fast-twitch muscle fibres but probably not to the same extent as cycling. Nevertheless, it is a reasonable form of exercise for those who like to walk, but it is very difficult to get a young adult’s heart rate over 130 beats per minute when sprint walking. Therefore, it is unlikely that sprint walking will result in significant reductions in belly fat.

Sprint stair climbing

Sprint stair climbing is a good form of interval sprinting as it is possible to get your heart rate over 130 beats per minute. The advantages of stair climbing are that it avoids pollution and traffic, and is cheap and time-efficient. Stair walking is a low-impact exercise, although descending is harder on joints.

The recommended posture is to keep a straight back, to avoid extending the knees and to place all of the foot on the step. You should ensure the staircase you choose is well ventilated and lit, has an even surface and offers good personal safety. We recommend you wear cross trainers rather than running shoes. The net energy cost in calories of stair climbing when walking has been estimated to be about 0.15 calories per 20cm step for a 70kg male. This is about 1 calorie for 7 steps. The optimal stair climbing walking rate has been estimated to be 90 steps per minute, so for 270 steps – 3 minutes of climbing – the energy cost is just below 40 calories. Coming down the stairs burns about a third of the energy as going up. Going up and down for 1000 steps per day would use up about 143 calories.

Stair climbing programs typically take about 12 minutes a day and are usually split into 3 4-minute sessions. Interval sprint stair climbing could include a 8-second stair climb and then a 1-minute toning exercise with the use of body weight and rubber bands. Other exercises could include push-ups against the wall and sit-ups.

Sprint running

Sprint running is another form of interval sprinting exercise. It is possible for experienced runners to do it on a treadmill, however this is a high-risk exercise. Because a treadmill is not able to accelerate and decelerate quickly enough for the 8-second/12-second protocol, you have to set the treadmill to sprinting speed and then jump off the treadmill while holding on to the side bars for the 12-second recovery phase before jumping back on to sprint.

Sounds too dangerous? Then try it on a running track. Sprint for 8 seconds and then easy jog for 12 seconds. Do this continuously around the track. If you don’t have a track, you can try sprint running on a flat, grassy surface. Map out a triangle and sprint for 8 seconds on one side of the triangle then easy jog for 12 seconds on the other 2 sides. This is probably the hardest type of interval sprinting; for some people, it will place too much stress on their ankle and hip joints.

Sprint arm ergometry

Upper-body interval sprinting training involves rapid movement of the arms. No research to date has invest-igated the effect of upper-body interval sprinting on muscle adaptations or clinical markers like blood and muscle lactate. It is likely, however, that this form of exercise will bring about changes that are similar to lower-body interval sprinting, although these changes will be to a lesser extent. Moving the arms rapidly can be achieved by a number of exercise modalities, although the most efficient is the stationary arm ergometer, a piece of equipment similar to a stationary cycle.

Sprint boxing

Boxing, especially with a partner, is another form of upper-body interval sprinting exercise. You can do this by yourself if you have access to a punching bag. Your partner can also hold a foam impact pillow while you punch continuously for 8 seconds. During the recovery phase, you can shadow-box slowly for 12 seconds – for example, by slow ducking and weaving. Heart rates during this form of exercise can easily get up to 150 beats per minute for young adults; thus, boxing may result in reduced belly fat, but, as mentioned, the ability of methods other than cycling to reduce belly fat is undetermined.

Sprint skipping

Skipping rope is a good form of interval sprinting exercise that you can do by yourself or with a partner. You will need a skipping rope, a suitable surface and good-quality footwear. Sprint skip for 8 seconds and then easy jog on the spot for 12 seconds. Heart rates during this form of exercise also can easily get up to 150 beats per minute for young adults.

Sprint swimming

Interval sprinting can be done in a swimming pool or in the ocean. A major limitation is timing the sprints or listening to sprint music. It would be possible with waterproof headphones, but counting the seconds as you sprint and recover is also an option. An example would be to sprint using freestyle for 8 seconds and then switch to easy breaststroke for a 12-second recovery period. It is difficult for non-athletes to get their heart rates up to 150 beats per minute while swimming, therefore it is unlikely that sprint swimming will result in a significant increase in catecholamines and, consequently, a reduction in belly fat.

Interval sprinting circuits

Interval sprinting circuit training is an excellent form of exercise that you can do by yourself, with a partner or in a group. Choose a combination of interval sprinting exercises from those listed above – for example, a good whole-body workout could include 5 minutes of boxing, 5 minutes of sprint skipping, 5 minutes of sprint rowing and 5 minutes of sprint cycling.

If you have time, it is possible to extend the 20-minute session by adding a resistance exercise between each sprinting exercise. For example, an interval sprinting circuit could include 5 minutes of boxing, 5 minutes of skipping rope, 5 minutes of rowing and 5 minutes of cycling. In between the sprinting bouts you could do 30 seconds of resistance exercises, such as push-ups, dips, crunches, biceps curls, lunges and so forth.

Monitoring your progress

To monitor your progress you need to record a certain amount of information. This information could include:

• heart-rate response during sprinting exercise
  
• heart-rate response during the cool-down
  
• pedal rate during bike sprinting exercise
  
• pedal resistance during bike sprinting exercise
  
• weight and/or body fat change
  
• waist circumference change
  
• abdominal width change
  
• waist skinfold site change
  
• lower- and upper-leg circumference change
  
• rating of perceived exertion during exercise
  
• aerobic fitness change, as assessed by a submaximal fitness test
  

Heart rate, pedal rate and pedal resistance have been previously described in this chapter, whereas body composition was outlined in chapter 2. Rating of perceived exertion is an easy but effective way of monitoring exercise intensity and has been used to prescribe exercise intensity in a variety of sporting activities and clinical settings. A rating of perceived exertion chart is typically used to measure people’s perception of how hard they are exercising (see Appendix D).