SESSION NOTES: Energy System Intervals (649)

Complete as many rounds as possible of the following. Resume each interval where you finished the previous. Complete the following work to rest intervals: 3x(30:120), 3x(120:240), 1x(300). 8 Kettlebell Swings, 4/6 Cal Ski Erg, 6 Box Jump Overs.


Programming Science:

This session trains multiple different aerobic and anaerobic energy pathways, improving your ability to use the phosphocreatine, glycolytic and oxidative energy systems to produce energy over varying time domains.

This session begins by training the shorter, more high intensity energy system, with subsequent intervals increasing in length and decreasing in intensity to train lower yield energy systems.

As a result, anaerobic, lactate and aerobic thresholds are trained.

The first (1:4 work to rest ratio) and second (1:2 work to rest ratio) sets of intervals require active recovery in order to buffer the hydrogen ions (the byproducts of anaerobic exercise) from the system to ensure maximal output in subsequent intervals.

The final set is a longer duration piece, moving more towards training the aerobic energy system.

The intervals progress from short to long to minimise the loss in intensity that would occur if the order were reversed (which would then reduce the benefits to the shorter, more intensive energy systems).

The movements programmed are simple movements with low skill requirement. They are low in complexity and also low in load, meaning the limiting factor of each session will be cardiorespiratory endurance, not skill or strength. The low volume of each movement further places the emphasis on cardiorespiratory endurance, rather than localised muscular stamina.

Further contributing to this effect is the very low interference between each movement (though there is a slight bias towards the lower body due to there being larger muscle beds there that will provide greater benefit to cardiorespiratory endurance). This creates a ‘blood shunting’ effect between different parts of the body, further building cardiorespiratory endurance.

Health and Body Composition Benefits:

Cardiorespiratory exercise has considerable health benefits, with this session creating favourable changes to cardiovascular disease (including reductions in blood pressure) and respiratory disease. This session will also lower your resting heart rate and increase blood flow to the brain.

As a result of this style of session, you will experience changes in blood chemistry, including favourable effects on cholesterol, blood glucose, triglyceride and lipid levels.

Although this session isn’t optimally effective as a stand-alone method of modifying body composition and weight management, it will aid in reducing levels of body fat when included in conjunction with your strength and resistance training based sessions.

Similarly, although this style of session doesn’t have as powerful a long term effect on your resting metabolic rate as resistance-based exercise, cardiovascular exercise at high intensities will put your body into a prolonged state of ‘EPOC’ (excess post- exercise oxygen consumption), meaning you’ll continue burning energy long after you finish training – further aiding healthy body composition.

Performance Benefits:

The primary benefit of training for cardiorespiratory endurance from a performance perspective is to improve the ability of your body to complete alternating and conflicting movements at very high work rates.

This session achieves this by training multiple energy systems which generates ‘ATP’ (adenosine triphosphate) which fuels movement. By completing this session and training these energy systems, we’re able to raise the threshold at which fatigue kicks in. This results in the session not only improving your work rate, but also improving your ability to sustain a higher work rate for longer, with less fatigue.

As a result of this session, you’ll experience performance-boosting changes in intramuscular substrate storage (increasing energy availability for muscle contractions) and increased enzyme activities (increasing the rate of energy delivery to the muscles).

Additionally, the repetitive muscle contractions create positive changes at a muscular level.

As a result of the shunting of blood between alternating and conflicting muscle groups, this session is very effective at improving your body’s ability to buffer hydrogen ions (the limiting byproduct of high intensity anaerobic exercise) at a systemic level.

The higher volumes will also increase capillary density in your muscles, allowing for efficient delivery of oxygen and fuel, and removal of waste products (further adding to the fatigue resistance).

These muscular changes also occur in the ventilatory muscles, improving breathing efficiency.

From a psychological point of view, if your pacing is correct, this session can be an effective method of entering a ‘flow state’, an optimal physical and mental zone which can help to maximise your performance.


Regardless of the length of interval, the strategy here should be to find the maximal sustainable pace (the highest speed you can maintain) for each interval. For the short intervals, this pace will be much higher than for the longer intervals.

How it Should Feel:

The first lot of intervals should still be at a high pace and will become uncomfortable in the final five seconds. The second lot of intervals will be the most uncomfortable, requiring you to maintain a consistently high work rate under considerable discomfort (muscle burn). The final long set will see you limited more by breathing than muscle burn.

Scaling Guidelines:

As this session is completed at a pace relative to the abilities of the individual, scaling is not necessary.

Modify around injuries with exercises as close as possible to the stimulus of the movement you’re modifying.

Common Mistakes:

Going too slow in the shortest intervals (these need to be max effort), and starting too fast in the second lot of intervals. If you are not able to maintain the same pace (your maximum sustainable pace) throughout the entire interval, you’ve started too fast and are not receiving the maximum benefit.