Scientists say there’s one type of training that will get you fit and strong fast and help you maintain your gains for longer – even when you take a break from exercise.

If you haven’t added HIIT to your routine, now’s a great time to take action. Research shows a good HIIT workout can be the ultimate one-stop-shop for all-around exercise results. It can deliver remarkable strength, lean muscle mass and aerobic fitness gains – fast. And here’s the clincher … this fascinating study suggests the strength and lean muscle gains you get from HIIT could have more sticking power than the gains acquired by other types of training.

Gains you get from HIIT could have more sticking power than the gains acquired by other types of training.

These findings come after researchers delved into whether short-term, single-mode exercise can improve physical fitness before a period of reduced physical activity. Specifically, they wanted to know the optimal way for middle-aged men to get in shape before an operation and stay fit and healthy during the post-operation recovery period.

During the study, participants did three morning workouts each week. Some did only resistance exercise, some did only endurance exercise, and some did only HIIT. The HIIT sessions varied between 13 and 23 minutes, whereas the resistance and endurance workouts were considerably longer. After six weeks, all participants spent 2.5 weeks ‘detraining’, which meant all their structured exercise efforts were put on hold.

Throughout the process, the researchers tested changes in everything from skeletal muscle fiber characteristics, body composition, muscle thickness, muscle strength, aerobic capacity, resting energy expenditure, and glucose homeostasis.

They found that regardless of what type of training they did, the six weeks of exercise rewarded all participants with increased strength and muscle fiber size. Some also enjoyed increases in lean mass and some saw improvements in aerobic capacity. Only those who did HIIT enjoyed strength and fitness gains across the board.

“This highlights how HIIT is a winning way to get strength, lean mass gains and aerobic fitness in one hit,” says Bryce Hastings, Les Mills Head of Research.

The study also showed that after a 2.5-week break, changes in aerobic capacity were lost but lean mass and strength gains were maintained by those who did resistance training and HIIT. “It indicates that with HIIT – and resistance training – you can keep the strength and lean mass gains even after you’ve stopped,” says Hastings.

This is good news if you’ve got a holiday on the horizon. Just like people preparing for surgery, chances are you want to go into your vacation feeling as fit, healthy, strong and happy as possible – and now you know HIIT could get you to that place, fast. And what’s more, you can enjoy a relaxing and restful break without worrying that your strength gains are depleting.

You can find more insights into how to maintain your fitness levels while taking a break from exercise here.

It's not just your strength and cardio fitness that will benefit from HIIT, a large Norwegian study has recently shown how HIIT may help you live longer too. And if that isn’t reason enough to jump into a heart-rate spiking sweat fest, check out these five reasons to give HIIT a go.


Research shows the optimal weekly dose of HIIT is just 30-40 minutes with your heart rate about 90 percent max. This means you can’t rely solely on HIIT to safely fuel your fitness – it should be teamed with longer-form endurance training for the optimal balance.


Try LES MILLS GRIT™, a science-backed HIIT workout shown to deliver rapid fitness transformation. Another unique spin on HIIT is LES MILLS SPRINT™ a low-impact workout that will significantly improve cardiovascular, metabolic and musculoskeletal fitness.