The Vocation Related Exercise (VRE) has recently been introduced into the SAF with the intention to improve combat fitness of soldiers in their respective vocation. Included in the VRE is the Speed Training (30:60 & 60:120), which is also a type of interval training. Some might wonder, why is there an increase focus on interval training? This change of focus was implemented after realising that short fast runs with heavy loads is more of a norm than long endurance run during combat operations.
The army's traditional method for improving running ability and cardiorespiratory endurance is doing long distance run. This method is very good for building up the aerobic fitness of the soldiers, however, the intensity of such training is not enough to build up the anaerobic fitness and muscular power of the soldiers.
Interval training has been shown to improve both anaerobic fitness and muscular power. Thus, including interval training into our army's physical training session will greatly enhance the fitness level of our soldiers.
The lactic threshold (LT) is the point at which the rate of lactic acid accumulation exceeds the rate of removal. This is the effect of increase utilisation of the anaerobic system during high intensity activity. When this happens, there will be an increase in acidity in the body which will lead to decrease in running speed. Running below the LT means that a person is running at steady state. This allows the person to sustain the intensity for a long period of time. The more a person exceeds the LT the shorter the run can be sustained.
In order to improve the LT, the person will have to be training at an intensity whereby high amount of lactic acid is accumulated. Improvement of LT is minimal while undergoing long distance training because the running intensity during distance running is below the LT and so the body does not experience high level of acidity. LT is always exceeded during interval training which leads to high acidity level in the body. The body adapts to such situation by increasing the acid buffering capacity, leading to an increase in LT. The increase in LT allows a person to endure working at high intensity for a longer period of time. It also means that a person can run at a higher pace more comfortably, leading to a better 2.4km run time.
Plyometrics is a form of exercise that is commonly used to improve muscular strength & power. This form of exercise involves lots of jumping and other forms of explosive and rapid movements. Such movements require the muscles to stretch and contract at a high speed and to maximise the elastic property of the muscles. Such training will allow a person to utilise the muscles elastic energy more efficiently.
If you look closely when a person sprints, you will realised that the movement is very similar to doing explosive jumps continuously. Both jumping and sprinting requires the muscles to stretch and contract at high speed and to maximise the use of elastic energy to produce explosive movements. Additionally, running at high speed also increase the recruitment of the fast twitch muscle fibers1 in the lower limbs. Thus, doing interval training can allow a person to gain similar improvement in muscular strength & power as doing plyometric training.
Improvement in muscular strength & power allows a person to run faster, jump further and bear heavier loads. This will lead to better shuttle run and standing broad jump results as well as feeling less fatigue while route marching with heavy loads.
1Fast twitch muscle fibers are responsible for explosive actions while Slow twitch muscle fibers are for endurance.
It is known to many people that running at 60-70% of maximum heart rate is the Fat Burning Zone. This is because at this intensity, the dominant energy system is the aerobic system. And the main fuel for aerobic system is body fats. What many people do not know is that fats are also burned during high intensity interval training (>90% max. heart rate). Furthermore, weight loss is dependant on the total energy consumed and not so much on which substrate is used. For the same amount of time, exercising at >90% max. heart rate will consume more energy than exercising at 60-70% max. heart rate. Additionally, recent studies on weight loss are targeting at the effect known as Excess Post-Exercise Oxygen Consumption (EPOC). This term tells us that after exercise we consume more oxygen because our metabolic rate post-exercise is higher than normal.
Therefore, the longer the duration of EPOC, the higher amount of calories will be burned. Studies have shown that exercising at high intensity cause longer duration of EPOC as compared to low to moderate intensity exercise.
Finally, it has been shown that high intensity interval training is beneficial in promoting muscle hypertrophy, i.e. gaining lean body mass. Increasing lean body mass will lead to increment in metabolic rate. This will provide a positive effect for long term weight loss.
It has been shown that doing high intensity interval training can lead to several physiological benefits including improvement in LT and muscular strength & power, and aids in weight loss. However, one should take note that training at such high intensity will cause high level of stress to the cardiovascular system and high impact to the joints. Therefore, personnel should avoid participating in such training for more than twice a week and each training should be at least two days apart.
Novice, overweight and obese personnel should start with moderate intensity aerobic training and strengthen their lower limb muscles by doing resistance training, before participating in high intensity interval training under proper supervision.