What HIIT is
High intensity interval training, usually shortened to HIIT, alternates short periods of hard effort with periods of rest or easy movement. A session might be a few minutes of warm-up, then a series of efforts such as 30 seconds of fast cycling followed by 60 to 90 seconds of easy pedaling, repeated several times, then a cool-down. The “high intensity” part is relative to you: it means effort that feels hard, where talking in full sentences becomes difficult.
The general idea behind interval training is that you can do more total hard work in a session when it is broken into pieces with breaks than you could in one continuous effort. It can be done with running, cycling, rowing, swimming, or body-weight moves like squat jumps or fast marching, depending on what your joints and fitness allow.
HIIT is one option among many, not a requirement. Plenty of people get good results from steady walking and basic strength work, and results vary from person to person.
Check first
Hard efforts raise your heart rate substantially. If you have a heart or blood pressure condition, other health concerns, an injury, are pregnant, or have not exercised in a long while, it is sensible to talk with a doctor or qualified professional before trying HIIT. If you feel chest pain, dizziness or unusual shortness of breath at any point, stop.
Build a base first
HIIT works best on top of some existing activity. If you are new to exercise, a few weeks of regular walking or other easy cardio, plus basic strength work, gives your body something to build from. Starting with hard intervals before your muscles, tendons and joints are ready is a common way to end up sore or injured.
Start gently
Early sessions should feel moderate-to-hard, not exhausting. A hypothetical beginner session could look like this:
- Warm up for 5 to 10 minutes at an easy pace.
- Do 6 rounds of 20 to 30 seconds at a brisk, challenging effort, each followed by 60 to 90 seconds of easy movement.
- Cool down for 5 minutes.
That is a short session overall. Using the walking or cycling you already know, the harder efforts can be as simple as a fast walk uphill. Beginners can also use a work-to-rest ratio that favors rest, such as 1 to 3, and shift it gradually. To gauge effort, perceived exertion on a simple scale works well: efforts might sit at a hard but controlled level, and the rest periods should bring your breathing back near normal.
If the efforts feel impossible to finish, shorten them or slow down. If you finish feeling you had a lot left, you can add a round or two the next time, one change at a time.
How often
Because HIIT is demanding, it is usually done sparingly. Many people include one or two sessions per week, with a day or more between them. More does not mean better; a higher volume of hard work tends to increase fatigue, soreness and the chance of overuse problems. Your other training matters too. If you lift heavy legs on Monday, an interval session on the bike on Tuesday may feel poor.
A sample week, purely illustrative:
- Monday: strength training
- Tuesday: easy walk
- Wednesday: HIIT session, 20 to 25 minutes in total
- Thursday: rest or gentle stretching
- Friday: strength training
- Saturday: longer easy cardio
- Sunday: rest
Keep the hard days apart and make the other cardio days easy. Many people find that an easy pace they can hold a conversation at, the talk test, is the right level for everything but the hard intervals.
Choose low-risk activities
Pick movements you can control while tired. Stationary bikes, rowing machines, incline walking and swimming are often easier on the body than jumping exercises, since there is less impact. If you try bodyweight moves, choose ones where good form is still possible when you are puffing: quick step-ups, fast marching, or modified burpees without the jump. Poor form and fatigue are a poor combination.
Recovery and warning signs
Plan for a decent amount of recovery after hard intervals. Sleep, regular meals and fluids all affect how you feel the next day. Some muscle soreness is normal when you start. Be cautious if you notice any of these:
- Sharp or joint pain, rather than muscle fatigue
- Persistent tiredness or poor sleep after sessions
- Performance getting worse over a couple of weeks
- A resting heart rate that stays higher than usual, if you track it
These can be signs to cut back, take extra rest or ask a professional. HIIT should leave you tired but generally recovered by your next planned session.
Is it worth including
The appeal of HIIT is that it can fit into limited time and adds variety. Its drawbacks are that it is tiring and can be hard to sustain if you dislike it. If you enjoy it, one gradual, well-spaced session a week can be a reasonable addition. If you do not, there are plenty of other ways to build fitness.