published : 20 Sep 2022 at 05:00 newspaper section: [Life](http://search.bangkokpost.com/search/result_advanced?category=news&xNewsSection=Life) An efficient way to burn calories, high intensity interval training (HIIT) alternates bouts of exhilarating exercise with recovery periods. Virgin Active members can sweat it out in the 45-minute Grid Training — a high intensity workout to strengthen muscles, increase durability, enhance agility, at each base. Pushing gym-goers outside their comfort zone, the class involves various physical activities and equipment such as dumbbells, barbells, exercis…