As a fitness professional, I have been asked this question way too many times and the question "Do I need to put in 45 minutes of HIIT to get maximum results?" .. the answer in short is NO!
Due to contrary belief that 45 minutes is the be and end all of busting your body to get great results, well it is not. In fact, what would you think if I told you that you only had to do a maximum of a of 80 minutes for the entire week!! Yes, only 80 minutes, and the best thing, it can be broken up over 4 workouts!! That's only 20 minutes max per session. But it keeps getting better, if you are time challenged, you in fact can break up those 20 minutes into 2 x 10 minute workouts over one day, one in the morning and one in the evening for example.
High intensity interval training or HIIT as it's also known, if performed right with ample rest in-between sets or completed circuits in a short period of time, 10 to 20 minutes, actually benefit your cardiovascular system way better than long drawn out sessions that leaves your body needing a longer recovery, up to 1 to 2 days. Not to mention how many injuries occur during long sessions due to the fatigue factor of overdoing it, that include muscle and tendon tears, simply because there is way to much work load placed upon the body, and lets face it, when you are super fatigued, and you have a stack more sets, reps and circuits to perform, your form goes out the door, your breathing is all over the place. Your chances of injuries increase due to a decrease in the body to perform at its strongest, and your brain going into a state of panic and forgetfulness because you are so determined to finish an exercise or circuit that all rational thinking goes down the drain, along with your results. If you have heard the saying of LESS IS MORE, it's because you don’t need more to get the best results.
Research has shown that shorter more intense workouts actually get way better results than longer drawn out sessions. Another interesting fact discovered through research is that participants that know they only have a 10 or 20 minute workout of HIIT to perform, actually train harder than those that train for over double the time!! TABATA is a prime example of short and sweet, but super challenging and with great results achieved. TABATA is based on 4 minutes, yes only 4 minutes. How it works is you perform, let's say everyones favourite, Burpees. You perform 8 x 20 second sets of burpees with a 10 second rest in between the 20 second set. Sounds easy, but when done to maximum effort, it will be the longest and hardest 4 minutes of your life. Depending on your fitness level, you need only perform 2 exercises, more if your fitness levels are higher, but 2 is all you will need as a first timer, TRUST ME. This will equate to only 8 minutes with let's say 5 minutes rest between each 4 minute round. That's a total time of only 15 minutes, and you can burn up to 225 calories. Research also has shown your body is still burning calories long after the workout is over - between 24 and up to 72 hours or 3 days after. Pretty incredible hey?! How good is that laying on the beach on your rest day and knowing you're still burning calories. This reaction to your body is called the EPOC effect. EPOC stands for EXCESS POST- EXERCISE OXYGEN CONSUMPTION. It is based on the amount of oxygen required to restore your body to it's normal resting level. EPOC refers to the elevation in the rate your body burns calories, long after your session. But not all is sugar coated, pardon the pun. When HIIT training is used to lose weight, keep lean, and to improve overall cardio conditioning, you still need to fuel your body with high nutritional foods and CAN THE JUNK, except maybe for a cheat meal, here and there, life's to short not to have the odd indulgence.
In short you do not have to train you BUTT OFF for 45 minutes in one big CHUNK, but smaller, time friendly intense workouts that you will enjoy more, get way better results and ultimately your body will recover faster and without the chance of injury you will most likely stick with it.
I hope this article gives you a little more clarity and you will enjoy and look forward to performing your future workouts a lot smarter.