What to Expect at Your First HIIT Class: A Beginner's Survival Guide

What HIIT actually is

HIIT stands for High Intensity Interval Training. The format alternates work intervals at 80 to 95% of your maximum heart rate with recovery intervals at 50 to 70%. A typical HIIT session has 6 to 12 rounds of 20 to 60 seconds of work, separated by 10 to 60 seconds of rest. The American College of Sports Medicine defines HIIT as work intervals at 80% or more of max heart rate. Anything below that is interval training, not high intensity. The 4 work-to-rest ratios you will see on a HIIT schedule: Tabata is 20 seconds work, 10 seconds rest, repeated 8 times for 4 minutes total. The 30/30 is 30 seconds work, 30 seconds rest. The 40/20 is 40 seconds work, 20 seconds rest. The 45/15 is 45 seconds work, 15 seconds rest. The shorter the rest, the harder the session. Read our complete fitness class glossary for how HIIT compares to every other format on a modern schedule. The honest opinion: most classes labeled HIIT are not actually HIIT. They are circuit training with intervals. True HIIT is so intense that 20 minutes is the upper limit. If your "HIIT" class runs 45 minutes, it is circuit training with a HIIT label.

What makes HIIT different from regular cardio

HIIT differs from regular cardio in two ways: time efficiency and the afterburn effect. Time efficiency: a 20-minute HIIT session produces cardiovascular gains comparable to a 60-minute steady-state cardio session, per the ACSM. This is why HIIT is the dominant format for busy professionals. The afterburn effect, technically called EPOC (Excess Post-exercise Oxygen Consumption), is the additional calorie burn that happens after the workout ends. HIIT produces 6 to 15% additional calories burned in the 24 hours after the session, per the American Council on Exercise. A 400-calorie HIIT session produces another 24 to 60 calories of afterburn. That is real but modest. The marketing claims of "burn calories for 48 hours after your workout" exaggerate the effect by 3 to 5 times. The real benefit of HIIT is not afterburn. It is the cardiovascular adaptation in half the time of steady-state cardio. VO2 max improves faster with HIIT than with moderate cardio, per multiple published trials. Insulin sensitivity improves faster. Blood pressure drops comparably. The trade-off is recovery: HIIT stresses the nervous system and requires 48 hours of recovery between sessions. Doing HIIT 5 days a week leads to overtraining, burnout, and injury. Two to 3 sessions per week is the maximum for most seekers.

What to wear to your first HIIT class

Cross-trainers, not running shoes. HIIT has lateral movement (skater jumps, lateral lunges, shuffles) and jumping (box jumps, burpees, tuck jumps). Running shoes have cushioned heels that compress under load and roll your ankle on lateral cuts. Cross-trainers like the Nike Metcon, Reebok Nano, NOBULL Trainer, or Under Armour TriBase have flat, firm soles that stabilize during lifts and grip during jumps. A good pair of cross-trainers costs $90 to $140. Fitted moisture-wicking clothes. You will sweat more than you thought possible. Cotton absorbs sweat and gets heavy. Synthetic blends (polyester, nylon, with spandex) wick and stay light. Fitted leggings or fitted shorts. Fitted tank or fitted tee. A sports bra with high support for women. HIIT has jumping, and a medium-support bra will not be enough. A headband for sweat. Sweat in your eyes during burpees is a real problem. A $10 sweatband from Nike or Lululemon solves it. Skip the lifting belt, the wrist wraps, and the knee sleeves for the first class. You do not need them. Read our what to wear to the gym guide for the broader wardrobe rules.

What to bring

A water bottle with marks every 8 ounces. HIIT produces 1 to 1.5 liters of sweat in a 45-minute session. You need to drink 16 to 24 ounces during the class and another 16 to 32 ounces after. A bottle with ounce marks lets you track intake. A small towel for face sweat and equipment wipe-down. Most studios require you to wipe down your station after class. A heart rate monitor is optional but useful for the first 4 classes. A chest strap monitor (Polar H10, Wahoo TICKR) gives accurate heart rate data so you can confirm you are hitting zone 4 and recovering to zone 2. Wrist-based optical monitors (Apple Watch, Garmin, Fitbit) are less accurate but adequate for beginners. A post-workout snack with 20 to 30 grams of protein. HIIT depletes glycogen and breaks down muscle. Eating within 30 to 60 minutes after class accelerates recovery. A protein bar, a shake, or Greek yogurt with fruit all work. Tyler, 27, in Chicago, brought a Clif Bar and a shaker bottle with protein powder to his first F45 class. He ate the bar in the car and felt recovered by the time he got home. The next week he forgot the snack and felt ravenous and shaky for 2 hours. The snack matters.

The 6 HIIT formats you will encounter

HIIT classes use 6 standard formats. Knowing them ahead of time removes 80% of the first-class confusion.

Most HIIT studios run a circuit format for beginner classes and mix in AMRAP or EMOM for intermediate. Tabata and pyramid formats are reserved for advanced classes. If your first class is a Tabata, ask the instructor for the scaled version. The format is harder than it looks.

The structure of a typical HIIT class

A standard 45 to 60-minute HIIT class has 3 parts. Warmup (8 to 10 minutes): dynamic movements to raise heart rate, mobilize joints, and prepare the nervous system. Expect jumping jacks, high knees, butt kicks, arm circles, bodyweight squats, and inchworms. The warmup is not optional. Skipping it is how injuries happen. Main HIIT block (20 to 30 minutes): the actual intervals. The instructor explains the format, demos every exercise, and offers modifications. You work through the intervals with the instructor cueing transitions. Cooldown and stretch (5 to 10 minutes): light movement to bring heart rate down, followed by static stretching for the worked muscle groups. The cooldown is also not optional. Skipping it leaves your nervous system elevated for hours and impairs recovery. Total class time: 45 to 60 minutes. Some studios run 30-minute express classes that compress all 3 parts. Some run 75-minute classes that extend the main block. Tyler, 27, took his first class at F45 River North in Chicago. The class was 45 minutes: 8-minute warmup, 28-minute HIIT block (2 circuits of 4 stations, 45 seconds work, 15 seconds rest, 3 rounds per circuit), and 9-minute cooldown. He modified 4 of the 12 stations and was sore for 4 days.

The vocabulary you need

HIIT has its own language. The terms you will hear in your first class: AMRAP (As Many Rounds As Possible, a format where you do as many rounds of a movement list as you can in a set time). EMOM (Every Minute On the Minute, a format where you do a fixed number of reps at the start of each minute and rest for the remainder). Tabata (a specific format of 20 seconds work, 10 seconds rest, 8 rounds). RPE (Rated Perceived Exertion, a 1 to 10 scale of how hard you are working). Max HR (Maximum Heart Rate, estimated as 220 minus your age). Work-to-rest ratio (the proportion of work time to rest time, like 2:1 or 1:1). Scaled (a modified version of the exercise for beginners or those with limitations). RX (as prescribed, the standard version of the workout without scaling). Rep (repetition, one execution of a movement). Set (a group of reps). Station (a single exercise position in a circuit). Round (one complete pass through all stations in a circuit). The instructor will explain these terms during the warmup. Ask if you do not understand. Most studios also have the terms posted on a wall.

The 7 things that will happen in your first HIIT class

These are the things nobody tells you. Forewarned is forearmed.

1. 1.You will sweat more than you thought possible. HIIT produces 1 to 1.5 liters of sweat in 45 minutes. Bring a towel. Wear moisture-wicking clothes. Cotton will be soaked through in 15 minutes.
2. 2.You will modify 3 to 4 exercises. The instructor will offer modifications for every exercise. Take them. There is no shame in scaling. The stimulus is the same.
3. 3.You will be sore for 3 to 4 days. Real sore. Stairs-will-be-a-problem sore. This is normal. The second class is the hardest to attend. Go anyway. Soreness drops to 1 to 2 days after class 4.
4. 4.Your heart rate will hit 95% or more of max. This is the point of HIIT. It will feel scary the first time. It is safe if you are healthy. If you feel dizzy, nauseous, or have chest pain, stop and tell the instructor.
5. 5.You will lose count of your reps. The instructor will cue transitions. Your job is to keep moving, not to count. If you lose count, do 5 more reps and move on.
6. 6.You will finish last in at least one round. Most HIIT classes run on a clock, not a rep count. You finish when the time is up. Slower finishers do fewer rounds. This is fine. Speed comes with practice.
7. 7.You will be hungry within 30 minutes. HIIT depletes glycogen. Eat a snack with 20 to 30 grams of protein within 60 minutes. Skip the snack and you will be ravenous for 3 hours.

How to scale: every exercise has a beginner version

Scaling is the practice of modifying an exercise to your level. Every legitimate HIIT instructor will offer a scaled version of every exercise. If they do not, leave. The standard scaling options: burpees become squat-to-stand (no pushup, no jump). Box jumps become step-ups. Jumping jacks become side steps. Push-ups become knee push-ups or incline push-ups (hands on a bench). Pull-ups become ring rows or banded pull-downs. Kettlebell swings become lighter weight or glute bridges. Mountain climbers become slow mountain climbers (no speed). Tuck jumps become high knees. Tyler, 27, scaled 4 of 12 stations in his first F45 class. He did step-ups instead of box jumps, knee push-ups instead of full push-ups, squat-to-stand instead of burpees, and ring rows instead of pull-ups. He still finished drenched in sweat and sore for 4 days. The scaling did not make the class easy. It made the class possible. By class 5, a week later, he only scaled 1 station (the pull-ups). The progression was fast because the stimulus was appropriate. The biggest beginner mistake is refusing to scale. Ego gets people hurt. The second-biggest mistake is over-scaling. If the instructor says use 20-pound dumbbells and you use 5-pound dumbbells, you will not get the stimulus. Listen to the instructor. They have watched 500 people do this workout.

Cost: $15 to $30 drop-in, $100 to $200 monthly

HIIT pricing in 2026 runs $15 to $30 for a single drop-in class, $100 to $200 for unlimited monthly at a mid-tier studio, and $160 to $199 for unlimited monthly at franchise studios like F45 and Orangetheory. F45 unlimited runs $169 to $199 per month depending on market. Orangetheory unlimited runs $159 to $199 per month. Barry unlimited runs $260 to $320 per month in major cities. Independent HIIT studios charge $100 to $160 for unlimited monthly. Drop-in rates at franchise studios run $28 to $38 per class. Most studios offer a new-student special: 1 to 2 weeks of unlimited classes for $30 to $60. Take it. Try 4 to 6 classes in 2 weeks. Find an instructor whose cueing you understand. Then commit to monthly. The break-even: if you attend 2 classes a week, unlimited monthly is cheaper than drop-in. If you attend once a week, drop-in or a 10-class pack is cheaper. The honest opinion: HIIT is the best-value group fitness format if you actually go 3 times a week. At $179 per month for 12 classes, F45 costs $14.92 per session. That is less than a personal trainer ($60 to $120 per session) and less than most boutique studios. The catch is the 3 times a week. Most drop-off is in month 2, when the novelty wears off and the soreness feels repetitive. Use FITT Finder Chicago or your own city page to find HIIT studios with intro specials.