HIIT has many benefits:
- Enhances fitness
- Significantly increases fat loss relative to steady state cardio
- Improves mental focus
- Can enhance muscle gain
Whilst excessive HIIT training can significantly inhibit testosterone levels, resulting in overtraining, if you receive sufficient recovery from each session, the effect will be negligible. The HIIT workout itself can actually help in the secretion of anabolic hormones to boost the rate at which hypertrophy is experienced.
Testosterone levels will primarily be improved through:
- Sufficient recovery
- High intensity heavy weight training
- Sound nutrition
If you have all of these aspects in check, the incorporation of HIIT for fat loss will not significantly impact your muscle maintenance (or gains) by any great degree. Keep in mind that if you reduce your caloric overload (or increase your caloric deficit), the rate of hypertrophy will most likely drop.
Now the main difference between females and males with respect to muscle gain is testosterone, something that is required for muscle synthesis. Females obviously have far lower levels. The good news for females is that cardiovascular training has no where near the potentially detrimental effect that it does on males with regards to testosterone levels. It is much easier for a male to overdo the cardio and thus see a reduction in testosterone levels.