Short answer
HIIT, or high-intensity interval training, is primarily a cardio training method. It alternates hard efforts with recovery periods and is defined by how you structure the work, not by the exercises. Because it can use bodyweight or weighted movements, it can feel like strength training, but it does not replace a progressive lifting program.
What is HIIT?
HIIT means short bursts of near-hard effort followed by rest or easier work. A session might use sprints, a bike, a rower, burpees or kettlebell swings. Group formats such as CrossFit use similar structures; see is CrossFit interval training. Sessions are often 15 to 30 minutes including warm-up. It is often described as time-efficient, but it is also demanding, so frequency matters.
If you are new to intervals, see conditioning cardio workouts for beginner formats.
What is strength training?
Strength training, also called resistance training, uses external load or bodyweight to challenge muscles, usually with controlled sets, rest periods and gradual increases in weight or reps over time. It is aimed at building strength, muscle size and bone and joint resilience.
HIIT versus strength training
| HIIT | Strength training | |
|---|---|---|
| Main goal | Cardiovascular fitness, work capacity | Strength, muscle, bone health |
| Structure | Timed work and rest intervals | Sets, reps and load |
| Progression | More work, shorter rest | Heavier load or more reps |
| Rest | Short | Often longer between sets |
| Fatigue | Heart and lungs, whole body | Targeted muscles |
When HIIT uses weights
Circuits with dumbbells, kettlebells or barbells can raise your heart rate and are sometimes called metabolic or conditioning circuits; see whether circuit training can build muscle. They may provide some muscle stimulus, especially for beginners, but light loads and short rests are generally less effective for building maximal strength than structured lifting with progressive overload.
Can HIIT replace lifting, or the reverse?
Neither fully replaces the other. HIIT improves aerobic fitness; lifting is the better tool for strength and muscle. Health guidelines generally recommend both aerobic activity and muscle-strengthening work on at least two days per week.
What if I only lift and do no cardio?
Lifting alone has real benefits, and it can modestly raise your heart rate during circuits or short rests. But you may miss out on the aerobic fitness benefits of dedicated cardio, such as endurance and recovery between sets. Even a couple of easy sessions per week can help. For options, see the best cardio to do in the gym.
The top cardio exercises
Common choices are brisk walking or running, cycling, rowing and swimming. HIIT can be done on any of them.
Combining HIIT and strength training
- Lift on 2 to 4 days per week.
- Add one or two short HIIT sessions, separated from heavy leg days when possible.
- Keep other cardio easy.
- If both happen on the same day, do the one you want to prioritize first.
Pacing hard intervals by effort is easier with a heart rate framework; see max heart rate training.
Cautions
HIIT is intense. If you are new to exercise, have a heart or joint condition, or are pregnant, speak with a healthcare professional first. Build up gradually and stop if you feel pain, dizziness or chest discomfort.
FAQ
What is interval training? Alternating harder effort with easier periods. HIIT is a high-intensity version.
Is HIIT good for building muscle? It may help beginners somewhat, but progressive resistance training is the more reliable method; see strength training for muscle gain.
How often can I do HIIT? Many people do well with one to three sessions a week, adjusted to recovery.