Everything you need to know about HIIT (High Intensity Interval Training)

[AdamGH]

I am 46 and not done much cardio
would HIIT be a bit much for me.
on first cycle at moment and trying to gain some quality muscle, have gained 10lbs up to now in first 2 weeks, would i be risking these gains??

Nope, go for it! You only need to do it 2-3 times a week.