What muscles does this HIIT workout target?

Your core, shoulders, hamstrings take the biggest hit, with secondary work through quads, spine, glutes. But here's what most people miss about hiit workouts: the primary target is your cardiovascular system, not individual muscles. A 2024 meta-analysis by Dupuit et al — found HIIT reduces visceral fat in perimenopausal women more effectively than steady-state cardio. The 14 exercises in this 15-minute session with Natalia Gunnlaugs are designed to keep your heart rate in the 80-90% zone for short bursts. That's where the metabolic magic happens. Your muscles are along for the ride — and they benefit too.

What equipment do I need for this workout?

You'll need: dumbbells, mat. Don't have these? water bottles, canned goods work as substitutes — I've coached women through this with filled water bottles and it works. The resistance is what matters, not the brand. Natalia Gunnlaugs shows form with standard equipment, but anything that adds load will do. Just make sure it's comfortable to grip — slippery objects and high-intensity moves don't mix. This pairs well with a core and cardio workout approach. This pairs well with a core strengthening exercises approach.

Is this workout suitable for beginners?

This is rated intermediate, so it assumes some baseline fitness. But Natalia Gunnlaugs offers modifications: Bring knees down to the mat if needed; Use body weight instead of dumbbells. If you've been training consistently for 2-3 months, you're ready. If you're brand new, start with a beginner-level workout in this series and work up. Nobody benefits from ego-lifting into an intermediate session on day one. This pairs well with a high intensity workout for fat loss approach.

How long is this workout?

Approximately 15 minutes, including warm-up and cool-down. Natalia Gunnlaugs wastes zero time — 14 exercises, no standing around, no 3-minute rest periods. The ACSM recommends 150 minutes of moderate or 75 minutes of vigorous exercise per week. Two or three of these sessions gets you there. That's 40-60 minutes per week of actual exercise. The rest of your week is yours.

Are there modifications available?

For every exercise. Natalia Gunnlaugs cues modifications as they come up: Bring knees down to the mat if needed; Use body weight instead of dumbbells; Reverse lunges instead of jumps — I'll say this once: using a modification is not failing. It's choosing the version that lets you maintain form for the entire set. A half-range pushup with a flat back beats a full-range pushup with a sagging spine every time. Pick the version where your technique stays clean.

How many calories does a HIIT workout burn?

The honest answer: it depends on your weight, fitness level, and actual effort. A 15-minute HIIT session typically burns 200-400 calories for a 140-170lb woman working at true high intensity. But here's what matters more than the calorie number: EPOC. Excess post-exercise oxygen consumption. Dupuit et al.'s meta-analysis found HIIT triggers metabolic elevation for up to 24 hours after the workout ends. So the calories you burn during the session are just the opening act. The real metabolic work happens while you're making dinner.

Is HIIT safe for women over 40?

Yes — with appropriate modification and a proper warm-up, which Natalia Gunnlaugs includes. A 2024 systematic review by Huynh et al — found aerobic exercise (including HIIT) significantly improves cardiovascular health in postmenopausal women with no increase in injury rates when progressed appropriately. The key phrase is 'progressed appropriately.' Start with the modification. Build up over 2-3 weeks. If you have joint issues, swap jumping for stepping. HIIT means high heart rate, not high impact. Those are two different things.

How often should I do HIIT workouts?

Two to three times per week, with at least one rest day between sessions. Your body needs 48 hours to recover from genuine high-intensity work. If you're doing HIIT every day, you're either not going hard enough or heading straight toward overtraining. Mandrup et al — demonstrated that three sessions per week was the sweet spot for improving insulin sensitivity in menopausal women. More wasn't better. Recovery is not laziness — it's where adaptation happens.

15 Minute Cardio Workout | HIIT Blast #9

Exercise Breakdown

14 exercises in Workout 9

Warm-up5 exercises

2m 6s