Fat loss
Researchers from Laval University in Québec, Canada, analysed how the two different forms of training (high and low intensity) affected body fat levels and muscle metabolism. The study took a group of young adults and divided them into two groups, the first was subjected to a 20-week endurance-training programme while the second did a 15-week high-intensity interval-training (HIIT) program.
 
Interestingly, they found that the group performing lower intensity cardio burnt more calories on average (120.4 mega joules) compared to the HIIT group (57.9 mega joules), muscle biopsies and body fat measurements revealed the HIIT programme resulted in greater fat loss and an increased metabolism.
 
This led researchers to conclude that high intensity training favours negative energy and lipid balance to a greater extent than exercise of low to moderate intensity. Moreover, the metabolic adaptations taking place in the skeletal muscle in response to the HIIT programme appear to favour the fat loss process.

Winner: high intensit
y

Insulin sensitivity
Insulin is required for the body to process glucose and though it has anabolic muscle building properties (especially post workout since it ‘shuttles’ nutrients to the muscles), too much of it has been shown to increase body fat. Insulin sensitivity is a term that relates to how well your body responds to the hormone insulin and, by extension, how well it processes glucose and stores body fat.
 
If you have ‘good’ insulin sensitivity your body will only require a small amount of insulin to process glucose, which means your body is less prone to storing body fat, however those with ‘bad’ insulin sensitivity require more insulin to process glucose, which makes them more likely to store body fat. One thing to bear in mind is that regardless of a person’s natural insulin sensitivity, exercise does improve it.
 
Researchers at the Medical College of Georgia, USA, took a group of obese adolescents with poor insulin sensitivity and divided them into two groups. One underwent a moderate intensity training routine for 30 weeks while the other did a high intensity training routine for the same length of time – both groups also received nutritional advice. Insulin sensitivity improved in both groups, but especially in the group performing high intensity training.

Winner: high intensity


Immune response
It’s widely agreed among strength and conditioning experts that low to moderate training can have a positive effect on your immune system, while high intensity training can have a negative effect. This is because high intensity training causes oxygen usage to skyrocket, increasing lactic acid accumulation in the muscles and prompting the body to pull alkaline reserves from bones. This can result in the immune system’s efficiency being reduced for anything from three to 72 hours. So, if you train often and are susceptible to illness it may be better to reduce the amount of high intensity sessions in your workout schedule and replace them with something of low to moderate intensity. 

Winner: low intensity

 
OVERALL WINNER: HIGH INTENSITY
 
This article was written by Ross Edgley of www.myprotein.com, the UK’s #1 online sports nutrition brand. Follow Ross Edgeley on Twitter at @rossedgley

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