Oct 24th, 2018

HIIT training: How much is too much?

There’s no denying that HIIT (high-intensity interval training) has made it into the mainstream of the fitness industry over the past few years, and its popularity has soared as more people realise its potential health benefits. These fast-paced, short workout sessions promise to burn more calories and build more muscle than a standard workout, and can even cause you to continue burning calories over the 24 hours after your workout. Sounds ideal, right?

But is there such a thing as too much HIIT? Can you do more harm than good by continuous back-to-back HIIT sessions? Here, we’ll go through what exactly HIIT is, and the best way to safely incorporate it into your workouts.

What is HIIT training and how does it work?

HIIT training involves alternating between very intense, quick anaerobic periods (where oxygen is not present and glycogen is used as fuel) partnered with slower recovery periods. During anaerobic exercise, your body builds up lactic acid which, over an extended period of time, results in a stitch or cramps. This is why anaerobic exercise is best done in short bursts. The best way to remember the difference is by bearing in mind that sprinting is anaerobic, while marathon running is aerobic.

Anaerobic exercise leads to a shorter workout, where you’ve efficiently used your body’s energy store to burn more calories. Many experts recommend this for those looking to burn fat and lose weight. A typical example of a HIIT workout can include a combination of:

  • Treadmill sprints
  • Stairmaster
  • Jump rope
  • Cycle sprints
  • High knee reps
  • Jumping lunge reps
  • Burpees

During the intense workout, where you’re working at your maximum capability, the heart is unable to pump blood around in a way which will provide all the muscles with sufficient oxygen. This anaerobic period results in molecular responses in most organs, triggering the biological changes linked with fitness, such as fat burning and increased muscle mass.

What are the health benefits of HIIT training?

These intense bursts of exercise outperform traditional cardio workouts when it comes to fat loss, as the training results in a surge in your body’s levels of growth hormones. In order to reap the benefits of HIIT training, you need to reach between 80% and 100% of your VO2max, which is the measurement of the maximum volume of oxygen that your body can use. You know you’ve reached this level when you feel like you can’t bring in as much air as your body needs. A good way to know you’re there is when it becomes difficult to hold a conversation, or talk in general, while working out.

A 2011 study by the University of Western Ontario found that interval training—where participants completed 4-6 30-second treadmill sprints with a few minutes rest in between each—results in more fat loss when compared to 30-60 minutes of steady-state cardio. HIIT also boosts the metabolism of the body, meaning that more calories are burned during rest periods over the next 24 hours following a workout.

The intense bursts of exercise also help build lean muscle mass, which overall means that the body burns more calories. Bodies with a higher muscle mass naturally burn more calories on a daily basis, even during resting periods, as more energy is required to fuel the increased muscle. In order to successfully complete a HIIT workout, you need to work at your maximum level of exertion, rather than coast along. This keeps your heart rate up, burning more fat in less time than a less intense workout session. HIIT training leads to an increase in lean muscle as it relies on body-weight exercises, such as burpees, mountain climbers, and walk down push ups, which is ideal for building muscle.

What are the health risks associated with HIIT training?

Continuing to perform back-to-back HIIT sessions without giving your body time to rest and recover puts a huge amount of strain on your muscles, which could damage them over time. A study by Jinger Gottschall at Penn State University found that giving yourself adequate time to recover between sessions improves your overall performance during workouts, and ensures that you benefit from positive results. Gottschall also noticed that individuals who had undertaken a high volume of HIIT training were unable to regularly reach their maximum heart rate, had a reduced sleep quality, and often complained of symptoms related to overtraining.

While HIIT training is suited for almost every lifestyle, there are some cases where it could be more difficult. Due to the very fast-paced and intense nature of the exercises, and the fact that you will need to push your heart rate as high as you can, it can be dangerous for some people to complete HIIT training without approval from a doctor. This includes:

  • People with a family history of coronary disease
  • Smokers
  • People with high blood pressure, diabetes, or high cholesterol
  • People with sedentary lifestyles
  • People who are obese or very overweight
  • Older adults who may not be used to exercising regularly

However, in these cases, once the basic fitness level has been improved, it is usually much easier to introduce small aspects of HIIT training to a workout without overwhelming the body, provided a doctor has approved. Even if you don’t have any health issues, people new to working out who are just getting into fitness should start slow in order to acclimatise themselves to working out in short, intense bursts. Those who are undertrained should get to a good baseline level of both cardio and strength training before going into HIIT, as this will make it much easier to handle intense workouts without causing any damage. This also makes it much easier to stick to the workouts, as you won’t be left feeling demotivated if you can’t get it straight away.

Regardless of your fitness level, it’s imperative that you warm up and prepare before a HIIT session—much like any workout. Many people go to the gym after a day sitting in the office, but without adequately warming up your muscles, you run the risk of causing yourself serious damage. You should also ensure you maintain the right posture during HIIT workouts, as it could cause you to pull a muscle, or sprain yourself. Keeping the right form is crucial, as it drastically lowers the risk of injury. A trained coach or instructor will be able to assist in getting the right form, and will also be able to spot any improper form, such as slouching, and help you to correct this.

How to recover from HIIT training

As well as properly warming up, cooling down and giving yourself recovery time is also important to ensuring you don’t run the risk of damaging yourself. As HIIT helps to build muscle, you need to give yourself time to recover, and give your muscles a rest.

Delayed onset muscle soreness, or DOMS, is the pain you feel after an intense workout, and is caused by microscopic tears in your muscles which naturally happen during a new workout. These tears are then repaired by your body over time, and more tissue is produced as a result, giving you more muscle mass. The pain generally starts 24-48 hours after a workout, due to an increase in blood flow to the muscle tears, which aids in recovery. However, this isn’t anything to worry about; even if you don’t experience DOMS, it isn’t a sign that you haven’t worked out hard enough.

There are things you can do to reduce and alleviate the pain, including drinking plenty of water before, during, and after your workout. You can also invest in a foam roller, which helps to massage muscles, soothing knots and relieving any tightness in your muscles. Epsom salt baths are also helpful in these cases, as they help to widen blood vessels to boost recovery. For the brave few, an ice bath, or plunging yourself into water as cold as you can bear, can also help to relieve muscle soreness, and reduce muscle inflammation and its effects on the body.

Is HIIT training safe during pregnancy?

Keeping fit during pregnancy is imperative to your own health, and the health of your baby. It can help you sleep better, improve circulation, boost energy levels, and ease the discomfort associated with pregnancy, including swelling and lower back pain. It also helps with labour, as it boosts muscle tone and strength, and can improve your fitness levels post-pregnancy. If you participated in HIIT training pre-pregnancy, you’re able to continue the workouts while pregnant, provided you’re experiencing a healthy pregnancy and have approval from your doctor.

During your first trimester, your body should continue to respond to HIIT as it did pre-pregnancy, however early pregnancy symptoms, such as morning sickness, fatigue, and cramping, can stop you from completing a full workout. This isn’t anything to worry about, as long as you remember to listen to your body, and only complete what you can comfortably do and avoid pushing yourself too far.

In your second trimester, you may find that your growing belly can stop you from doing some of your usual moves. An experienced trainer will be able to offer alternative exercises for you to take part in, rather than risk damaging yourself. It’s important to remember that pregnancy impacts joint stability, balance, coordination, and even heart fluctuations and blood pressure, so you should take extra care to pay attention to your body.

Exercise during your third trimester can help prepare your body for labour, however you should take extra care with the types of exercise you do, as you don’t want to restrict the blood flow to your growing baby. In general, the fitter you are, the “easier” your labour will be. Keep active with exercises that work your pelvic floor, such as kegels, to help you with delivery.

It’s important to stay well hydrated throughout your pregnancy, and even more so while working out. Dehydration during pregnancy can cause preterm uterine contractions and, in extreme cases, preterm labour. An extra long or strenuous workout can also decrease the amount of blood flowing to your uterus, so ensure you don’t overdo during a session, and take regular breaks if you feel you need to.

What should you eat before and after a HIIT session?

Your body needs a good energy source to get you through a HIIT workout, which makes you work at peak intensity. Aim to eat at least 45 minutes before a workout, which gives you time to digest your food so you won’t cramp or feel sick while training. You also don’t want to have a full or heavy stomach during your training session, so the best way to eat is light and clean. Go for slow-burning carbs and protein, such as:

  • Protein bars
  • A couple of handfuls of nuts
  • Fruits
  • Natural yogurt
  • Grain-based bread
  • Oatmeal
  • Healthy cereal

Following an intense HIIT session, you’ll need to eat the right foods in order to fuel your body to keep going through the day, leaving it ready to repair itself. However, you won’t need to load up on extra fuel like an endurance athlete. Go for a small protein-based snack within 20 minutes of your workout to give your muscles the nutrients they need to recover quickly, as well as plenty of water. This gives you time and energy to prepare a full, nutrient-rich, post-workout meal.

Stick with your basic carbohydrates, protein, and greens mix for a balanced meal, but be smart about your choices to get as many key nutrients as you can:

Getting enough calcium maintains proper muscle function, which you will need in order to maintain and improve your fitness levels. Good sources of calcium include seeds, cheese, yogurt, sardines, beans, lentils, leafy greens, and tofu.

Selenium acts as an antioxidant, which is vital as an intense workout increases the potential for cell-damaging free radicals to work their way around your system. Antioxidants reduce oxidative stress, speed up recovery, and enhance your overall performance. Foods rich in selenium include fish, eggs, brown rice, barley, baked beans, chicken, turkey, and mushrooms.

B vitamins
Your body relies on B vitamins to produce the energy you need for workouts, as it relies on them to convert food to fuel, and maintain a healthy nervous system function. Foods rich in B vitamins include whole grains, red meat, fish, eggs, cheese, lentils, seeds, dark vegetables, and fruit.

Vitamin C
Ascorbic acid or L-ascorbate is also known as vitamin C, and is essential to the human body. The antioxidant helps protect your body against free-radicals, and can help reduce the damage to your body caused by pollutants and toxic chemicals. Vitamin C is crucial for repairing and growing tissue in your body, including cartilage, bones, and teeth, and is used to produce collagen, which is helpful for ligaments, skin, tendons, and blood vessels. Foods high in vitamin C include chilli peppers, citrus fruits, yellow peppers, blackcurrants, kale, and broccoli.

Whether you’re looking to improve your fitness levels, or just want to find a new exercise to incorporate into your workouts, HIIT training can be a great addition. However, you should be mindful of the risks associated, remember to stay hydrated, and listen to your body. If a workout is getting too much, it’s better to take a break and rest before continuing, rather than risk injury.

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