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High Intensity Interval Training – Part 3 Home Subscribe Email Print


So how will cardio help me increase my muscle size? Well we all know that cardio can be counter productive for someone looking to increase their lean muscle mass, however, this is in relation to continuous, long, slow distance cardiovascular training. I am going to talk about High Intensity Interval Training (H.I.I.T) – short bursts of high intensity cardio followed by a recovery period, with an overall sessio time of no greater than 30 minutes. But still how is this meant to help? Well it will help by increasing the efficiency of your body to work as a muscle building powerhouse – and here is how:



A study has shown that following just 2 weeks of H.I.I.T in a test group of young men with an average age of 21 there was a 14% reduction in the recovery time of Phosphocreatine (PCr). PCr is the energy carrying molecule that supplies energy in the form of ATP to the muscle cell for the first 2 to 7 seconds of intense activity. So what this means is a quicker turn around from energy delivery to energy reloading and redelivery. And guess where the energy is utilised? In the body’s ‘Powerhouses’ – the Mitochondria!!! And as we learnt earlier in Part 1 of this series, H.I.I.T stimulates the body to ‘grow’ more mitochondria (it improves our oxidative capacity or ability to utilise oxygen and produce energy). So we’ve got the Coal Trucks (PCr) being reloaded more quickly and we’ve got more fuel burning Power Plants (Mitochondria) for them to deliver to. This is coupled with an elevated re-uptake of Potassium from the interstitial space (outside a muscle cell) – the little Sop-Go men of the muscle (Stop = Potassium K+ & Go = Sodium Na+). When a message is received from the brain to contract the Stop-Go men trade places. Lots of Go men (Sodium) rush into the cell causing a positive charge and initiating muscle contraction (they direct the Coal Trucks to the Power Plants) . The Stop men (Potassium) head outside for lunch. However, while the Potassium is outside in the interstitial space they have been shown to decrease the excitability of the cell and the contractility – basically stop traffic out there as well. So they need to be sent back inside and the Go men outside so we can start the process all over again. Both endurance based training and H.I.I.T training have shown to improve the body’s ability to elevate Potassium re-uptake, however, H.I.I.T does this in 90% less time and with a lower impact on the immune system.

This increase in Potassium re-uptake also helps delay the onset of muscle fatigue with studies showing that with 6 weeks of scheduled H.I.I.T subjects performed resistance training for 28% longer than subjects performing the same resistance training but no H.I.I.T.


H.I.I.T has been shown in studies to increase the area of Fast Twitch Muscles fibres (Type IIb). These are the muscle fibres predominately targeted when training for an increase in muscle mass. By increasing the area of these fibres you are increasing their contractile force – basically H.I.I.T makes your Fast Twitch muscle fibres contract harder and faster.

So, let’s put this all together – H.I.I.T decreases recovery time, delays fatigue, improves our muscle fibres and improves energy production & utilisation. Now when it comes to lifting weights to increase your muscle size through hypertrophy training these improvements sure would help, right? of course!

Include 15 to 30 mins of H.I.I.T into your training schedule once or twice a week, either on your rest days or at the end of a weights session to reap the benefits. It’s as simple a 30 sec sprints with 30 – 60 sec walking recovery. If you want more information see one of our friendly gym staff.

Compiled by Rob Bonser.

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