Anna Evans

Science of HIIT by Ingrid S. Clay

Find out more about the flexibility of HIIT and the benefits it can bring to physical and mental health.

Science of HIIT

The book has gotten 4.20 ⭐️ on GoodReads.

High-Intensity Interval Training, commonly known as HIIT, is a leading method for burning fat and toning the body. HIIT alternates between intense anaerobic exercises and less intense recovery periods. It combines bursts of dynamic cardiovascular activity with strength-building movements, offering a complete routine in as little as 20 minutes.

Science of HIIT: Understand the Anatomy and Physiology to Transform Your Body’ provides detailed anatomical illustrations and instructions for proper execution, catering to beginners and fitness enthusiasts alike. With the information in this book, you’ll build your knowledge and confidence to design an effective HIIT workout tailored to your needs.

Author’s background

Ingrid S Clay is a Celebrity Personal Trainer, Master HIIT Group Fitness Instructor, Competitive Bodybuilder, and Plant-Based Chef with over a decade of experience in Fitness and Wellness.

Ingrid S Clay (r)

She holds degrees in Physics and Electrical Engineering, and an MBA in International Marketing from the Simmons School of Management, shaping her unique approach to fitness.

After working as an Electrical Controls Engineer, Ingrid pursued her passion for wellness and founded ISC Wellness. She crafts science-based fitness programs and travels worldwide as a Trainer, Coach, and Chef. Ingrid has been featured in various publications, including Well + Good, Essence, Livestrong, Fabletics, and PopSugar Fit.

As the owner of ISC Wellness, Ingrid also runs a fitness app with live and pre-recorded workouts. She serves as a Lululemon Brand Ambassador and the Director of Fitness at CAMP, a boutique fitness studio in Los Angeles. Additionally, Ingrid actively volunteers at the Watts Empowerment Center, providing health and wellness services to underprivileged children in the Watts Community.

What is the book about?

The first section of the book explains how HIIT improves cardiovascular fitness, raises metabolism, and builds and tones muscles. It also provides guidance on fueling workouts with the correct macronutrients.

The main section of the book contains a comprehensive collection of HIIT exercises targeting different body parts, with modifications for various fitness levels. Each exercise is accompanied by detailed instructions on proper form and common mistakes to avoid.

The book concludes with easy-to-follow routines for beginners, intermediate, and advanced levels.

Key takeaways from ‘Science of HIIT’

1HIIT is more effective in burning fat than steady cardio

Studies have demonstrated that brief intervals of high-intensity training are more effective in burning calories and fat than hours of steady-state cardio. Even just 10 minutes of maximum effort during a HIIT workout can be sufficient.

The reason behind this enhanced effectiveness lies in the fact that HIIT keeps your body guessing. During extended steady-state cardio, the body adapts and enters a metabolic state to conserve energy. In contrast, HIIT’s varying heart rate and energy output prevent the body from finding this steady state, resulting in a sustained higher rate of calorie burning even during post-exercise recovery.

2HIIT supports the immune system

Aside from its calorie-burning advantages, HIIT also offers immune support. Various theories suggest that exercise may improve immune function. It is believed that increased blood and lymph fluid flow from exercise may aid in the circulation of immune cells throughout the body.

Additionally, exercise’s role in reducing inflammation may also support compromised immune function caused by chronic inflammation. Furthermore, exercise has been proven to reduce mental stress, which can negatively impact the immune system.

3HIIT is a very equipment-friendly

The main focus of almost all HIIT exercises is body weight resistance, which involves engaging muscles to counteract gravity acting on your body’s weight. This aspect of HIIT makes it a highly accessible form of exercise as it requires minimal equipment and can be performed at any time and nearly anywhere.

4HIIT improves your cardiovascular efficiency

HIIT workouts enhance cardiovascular efficiency in multiple ways. They train the heart to beat faster and pump more blood with each beat. Additionally, they increase the overall volume of blood and the amount of oxygen-carrying haemoglobin. Moreover, HIIT improves the density and function of capillaries around muscles.

5HIIT workouts come with a bonus: the afterburn effect

HIIT workouts are short but highly effective at burning calories due to the afterburn effect or Excess Postexercise Oxygen Consumption (EPOC). This extended period of raised metabolism can last up to 24 hours after the workout.

Proper nutrition, with four to five balanced meals spaced evenly throughout the day, supports this recovery process. EPOC facilitates physiological adaptations like muscle growth and improved respiratory efficiency, making HIIT a powerful and efficient workout.

6HIIT effectively promotes muscle growth

As we age, the number of satellite cells, responsible for muscle regeneration, naturally decreases. Regular muscle activation through training is crucial, especially after the age of 30, to counteract this decline and preserve muscle mass as we get older.

HIIT workouts promote muscle growth, tone muscles, and preserve lean mass by increasing fast-twitch fibres. The process involves mechanical tension, fatigue, and damage during intense training.

7HIIT has a profound impact on the brain-body connection

Exercise influences both our mental and emotional well-being. By increasing blood flow and oxygen supply to the brain, exercise fosters a more energised and positive mental state. Hormones released during exercise contribute to a sense of happiness, while beneficial proteins called neurotrophins help maintain healthy brain cells and stimulate the growth of new ones, as supported by research from the Harvard Medical School Journal.

The positive effects of exercise on the brain extend further. Oxygen levels and blood vessel growth increase in brain regions responsible for rational thinking, physical abilities, and social skills.

Concurrently, exercise reduces stress hormones like cortisol, promoting the release of neurotransmitters like serotonin and norepinephrine, which contribute to improved mood and reduced stress.

8Proper nutrition is crucial for HIIT practitioners

For those aiming for weight loss through a HIIT program, proper nutrition is crucial for adequate energy levels and long-term physical transformation. To achieve the right balance, prioritise whole foods that release energy slowly and come with fibre and micronutrients, such as whole grains, vegetables, and fruits (in moderation due to sugar content). Protein should make up around 20% of daily intake, sourced from plant-based options like pulses, nuts, soy, as well as meat, fish, and dairy. Embrace mono- and polyunsaturated fats without avoiding fats altogether.

Table of contents

  • Introduction
  • The benefits of HIIT/Powering your HIIT workout/Improving your cardio fitness/The HIIT “afterburn”/How muscles work/How HIIT promotes muscle growth/Muscular anatomy/HIIT training and the brain/Feeding your HIIT
  • Introduction to the exercises/Terminology guide
  • High plank to low plank/Variations/Swim plank/Mountain climber/Variations/Bear plank/Variations/Sit-up/Crunch/Variations/Transverse abdominal ball crunch/V-up/Variations
  • Push-up/Variations/Overhead triceps extension/Variations/Dumbbell biceps curl/Variations/Dumbbell front raise/Variations/Dumbbell lateral raise/Military shoulder press/Variations/Dumbbell rear deltoid fly/Variations/Dumbbell bench press/Dumbbell chest fly
  • Squat/Variations/Right and left split squat/Variations/Crab walk/Alternating snatch/Alternating lateral lunge/Variations/Calf raise/Step-up with dumbbells/Alternating toe tap/Single-leg deadlift/Glute bridge/Variations
  • Skater/High knee/Variations/Squat jump/Variations/Tuck jump/Box jump/Single-leg forward jump/Football up and down/Burpee/Bear crawl
  • Jack press/Push-up and squat/Push-up and tuck jump/Bear plank and push-up/High plank, ankle tap, and push-up/B boy power kicks/Military press and overhead triceps extension/Bent-over row and hammer curl/Rear deltoid fly and triceps kickback/Sumo squat and hammer concentration curl
  • Getting started/Planning your training/Following and creating your own routine/Weekly training planner/Warming up and cooling down/Workout routines/Beginner/Intermediate/Advanced
  • Glossary
  • Index
  • Bibliography
  • Acknowledgments
  • About the author

Strengths and weaknesses, according to readers’ reviews


  • Provides CGI artworks depicting all the main HIIT resistance exercises – from burpees to plank jacks and variations that add or reduce the challenge.

  • Offers training programs, tailored to different abilities and goals, and workouts with a progressive increase in challenges over weeks and months.

  • Includes easy-to-follow infographics that explain the science behind efficiency of the HIIT training.

  • Doesn’t have a lot of frills and unnecessary filler information, the book is straight-to-point.


  • The majority of the readers left only good reviews and didn’t express any specific negative feedback on the book.

Best quotes from ‘Science of HIIT’

“If you don’t use them, you lose them... or they will go dormant. Our satellite cells naturally reduce in number as we get older, but training counteracts this decline. It’s important for people to activate their muscles on a regular basis once they reach the age of 30, or face the possibility of losing the ability to regenerate muscle mass as they age.”
“Everyone’s body responds differently to training. Focus within on your own effort and intensity and follow each routine closely. The more you put into your workouts, the faster you will see results and a change in your body.”

Final takeaway

Science of HIIT: Understand the Anatomy and Physiology to Transform Your Body’ is a great resource for beginners and experienced athletes alike. It covers everything from creating personalised training programs to understanding the mechanics of HIIT exercises and achieving weight loss and toning goals. As the readers progress, they can increase the intensity and duration of the exercises, making this book a valuable resource for years to come.

Where to buy

You can buy ‘Science of HIIT: Understand the Anatomy and Physiology to Transform Your Body’ on Amazon, where it’s available in paperback and Kindle formats.

Healthypedia FAQ

HIIT stands for High-Intensity Interval Training. It involves alternating short bursts of intense exercise with brief recovery periods.

Yes, HIIT can be effective for weight loss due to its high calorie-burning potential and ability to boost metabolism.

While HIIT can be beneficial, it may not be suitable for individuals with certain health conditions. It's best to consult with a healthcare professional before starting a HIIT program.

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