Exercise explained: from HIIT to circuits

Amy Wood - Nutritionist | 05 Apr, 2022

In the world of fitness there are various types of exercise to choose from. You'll have heard terms like HIIT and resistance training – but what actually is each type and who is it good for?

Ultimately, we exercise to improve our overall fitness. The term 'fitness' incorporates lots of different aspects, it's not just being able to run for 30 minutes for example. Fitness can be broken down into aerobic fitness, muscular strength, muscular endurance, balance, flexibility, power and body composition. Being physically fit requires a level of fitness in all of these areas, and this comes from regularly undertaking a variety of different types of exercise.

Here I'll discuss the most common types of activity and how they can benefit you.

Cardio/aerobic exercise

Cardio exercise

What is it?

Cardio is essentially any activity that increases your heart rate and breathing rate. So, it is anything from walking, to running, or swimming, or cycling to name a few. This type of activity is primarily focused on challenging our heart and lungs, rather than targeting specific muscle groups.

Cardio can be performed at various intensities, with the intensity being determined by how hard your heart and lungs are working.

Monitoring your heart rate is the easiest way to determine the intensity you're working at, with a higher heart rate indicating a higher intensity. Different heart rate zones define the different intensity levels, and these are based on a percentage of your maximum heart rate. There is a simple formula you can use to estimate your max heart rate which is 220 minus your age. So as a 35 year old, my max heart rate should be around 185 beats per minute (220 – 35 = 185).

This is a guide however, as everyone is different, and it may actually be that your max heart rate is higher or lower than this. I know mine can go up beyond 190 beats! Your max heart rate is individual to you and is not necessarily an indicator of fitness.

Heart rate zones

  • 50-60% of max HR = very light
  • 60-70% of max HR = light
  • 70-80% of max HR = moderate
  • 80-90% of max HR = intense
  • 90-100% of max HR = maximum

Rate of perceived exertion

Another way to determine the intensity of your workout is to consider your rate of perceived exertion. This is essentially how hard you feel you are working. The simplest method used is to follow a scale from 1-10, where 1 is very light work and 10 is maximum effort.

What are the benefits?

Cardio is a simple form of exercise which can often be carried out with minimal equipment, e.g. going for a run or walk – so it's easy for most people to do. It is extremely beneficial for our heart health as it challenges the heart and results in adaptations which make the heart stronger and more efficient. Cardio can burn lots of calories too depending on the intensity performed, as it's often carried out for an extended period of time – this makes it a good choice for anyone wanting to burn additional calories for weight loss. Regularly doing cardio exercise can also boost our mood and improve our sleep quality!

Resistance training

Resistance training

What is it?

Resistance exercise is exactly as described – anything that requires your muscles to work against a resistance. This can be resistance created by your own bodyweight, or by external factors such as resistance bands or weights.

If you're new to resistance training, it can be good to start with exercises which utilise your own body weight – examples are squats, push-ups, pull-ups, dips or lunges. Using your body weight can be a good way to place a demand on your muscles without overburdening your body too soon with very heavy weights.

As you get more experienced in performing certain bodyweight moves, you can introduce more resistance through resistance bands or light weights. Resistance bands are a good place to start as they allow you to add small amounts of extra resistance safely, as you can only achieve what you're able to in terms of working against the resistance. Whereas picking up free weights which are too heavy can lead to injury through incorrect form – so it's best to build up to these and start with lighter weights.

Resistance training that uses mostly bodyweight exercises will help to build muscular endurance and power, depending on the exercises undertaken. It can be more difficult to build a lot of muscle size and huge amounts of strength with body weight alone, due to the finite amount of resistance that can be applied.

What are the benefits?

This type of exercise challenges our muscles and ultimately creates adaptations in our muscles which lead to improved fitness over time. When we make our muscles work against a resistance, a small amount of damage is caused to muscle fibres. This damage initiates a healing response which ultimately results in muscles fibres increasing in size. Using our muscles to perform specific exercises also leads to neuromuscular adaptations so that muscles are more capable of performing certain movements due to the development of more neural pathways. So ultimately resistance training leads to stronger and potentially bigger muscles, which helps with general stability and the ability to perform various movements efficiently.

Building muscle mass through resistance training is great for maintaining a healthy metabolism too. This is because muscle mass is metabolically active, meaning it burns calories even at rest. So the more muscle we have, the more calories we burn day-to-day.

Resistance training is also great for boosting our mood and sleep quality and can help maintain bone health through improving bone density thanks to the weight bearing aspect.

Strength training

Strength training

What is it?

Strength training is a form of resistance training that is focused around lifting heavier weights to help build muscle strength and size. When it comes to getting stronger and building muscle, it is necessary to create a certain amount of resistance which can be achieved through lifting weights either using a machine or free weights. This means progressing your training above body weight or resistance band exercises, to ensure the required stress is placed on the muscles to result in increased strength and muscular hypertrophy (growth).

The number of repetitions of an exercise you can perform before fatigue will generally define whether you're lifting weights to build endurance, strength, or size. Below is the guidance for reps (repetitions) and sets (how many groups of repetitions) of each exercise to achieve specific fitness goals.

  • Muscular endurance – 12-20 reps for 3-4 sets
  • Muscular hypertrophy – 8-12 reps for 3-4 sets
  • Muscular strength – 6-12 reps for 3-4 sets

As you can see there is some overlap! Performing 12 reps of each exercise would result in some improvements in endurance, strength and size for example. But if your main goal is to build strength, then fewer reps at a higher effort would focus on this more. Or if your main aim is to build size, then the 8-10 rep mid-range would be best suited to this. In all cases, it's important that the resistance selected is enough that you are only just able to finish the last set of full reps.

What are the benefits?

Lifting heavy weights to build additional strength and size is really beneficial for weight loss and maintaining a healthy weight. Strength training, while it may not burn as many calories as cardio in the moment, has an afterburn effect due to the stress placed on the muscles, which makes it a good calorie burner in the long term. It also helps build more lean muscle tissue, which as explained above, results in a higher metabolic rate. Building strength and muscle also helps with stability as we age, which reduces the chance of injury.

As with any form of exercise, strength training is beneficial for our heart health as it creates extra demand on our cardiorespiratory system. It can also improve mood, sleep and overall quality of life. Strength training or resistance training is definitely something everyone should be doing if they can as it is the best way to combat the changes to our body composition and metabolism as we age. Many people are concerned that lifting weights will make them bulky, but this really isn't the case. Building significant amounts of muscle is very challenging and would require huge amounts of training and discipline. Incorporating some resistance style exercise into your routine can simply help to build a healthy amount of muscle and 'tone' and improve your overall health going forward. The benefit of 'tone' is a leaner appearance even though your body weight may not actually be lighter.

High intensity interval training (HIIT)

High intensity interval training

What is it?

HIIT is a type of exercise where you work at maximum or nearly maximum effort for a short period of time, followed by a rest or active recovery (low-intensity exercise) period – and you repeat this work/rest pattern for the duration of your workout. HIIT sessions tend to be much shorter in duration than cardio or resistance training sessions as they are very intense. Anything from 10-30 minutes is the norm and can result in significant fitness gains.

HIIT can be anything from sprint intervals to bodyweight based exercises performed at a high intensity. This means it can be helpful in targeting specific muscle groups or simply targeting our cardiovascular system through a more aerobic based session.

HIIT has become increasingly popular in recent years as people are now aware of the benefits of high-intensity short-duration workouts, which can be extremely convenient in our busy lives.

What are the benefits?

A 20-30 minute HIIT session has been shown to produce the same health benefits as a 40-60 minute steady state cardio session. This makes it hugely appealing for anyone with limited time. Thanks to the intensity of these workouts, HIIT can create a big calorie burn, and even though you may be exercising for a shorter duration overall, the afterburn effects can be significant. HIIT has been shown to elevate metabolic rate for hours after the exercise has finished – much longer than a gentle jog would – so it's a great choice for people wanting to burn extra calories for weight loss.

One thing to consider with HIIT is how frequently it is carried out. The high intensity nature of this type of exercise means it can cause a rise in cortisol levels (the stress hormone), so it should not be done too frequently. If you're new to exercise, build up to one HIIT session per week of 20-30 minutes duration. For more experienced exercisers, 2-3 HIIT sessions per week would be fine – but these should be separated by 1-2 rest days.

Circuit training

Circuit training

What is it?

Circuit training is a type of exercise where you complete short periods of work at various different exercise stations, in a circuit. This type of exercise can target lots of different muscle groups, as well as incorporating resistance training and cardio into one session. Typically, you move around a circuit of 8-12 exercises, completing 1 minute of each exercise. After one circuit you get a period of rest and then complete the circuit again a further 2-3 times.

If a circuit is designed well, you can achieve a lot in a short session, as it's possible to sustain a level of work for a long time without tiring too much. For example, if the first station was squats, followed by a plank and then push-ups, the main muscle groups being used at each station would change with each exercise, making it easy to continue to work at a higher intensity.

What are the benefits?

Circuit training is great for achieving a lot in a short amount of time as you can maintain a high level of output throughout. It is a great allrounder, as the exercise stations can be designed to target all the main muscle groups as well as some cardio based activities. It's versatile too, as the stations can be whatever you want – so you can create the perfect circuit for your goals, making it great for improving cardiovascular fitness, muscular strength, endurance and size. It's also a good calorie burner thanks to its high intensity nature, so great for those wanting to lose a few lbs.

Other areas

As well as the various exercise types discussed above, it's important to work on other elements of fitness such as flexibility and core strength. Ensure you complete an appropriate stretching session at the end of each workout while your muscles are warm, specifically targeting those muscles which were heavily utilised in the session. This will aid recovery, as well as helping to improve flexibility over time. Flexibility is important to avoid injury and improve range of motion, to ensure movements in various planes of motion are achievable throughout life.

Core strength is also hugely important! Many activities will require a certain amount of core work as we naturally use our core muscles to stabilise ourselves. But specific exercises such as ab crunches, the plank and back raises will help to target the deep core muscles around our midsection which are essential for maintaining form and protecting us from injury.

Which exercise is best?

As you can see, the various different types of exercise all come with their own benefits, so ultimately the best training plan would incorporate elements from each. Following an exercise program which includes some lighter steady-state cardio, a HIIT session or two and a couple of weight training sessions – as well as core training and stretching – would be ideal. This ensures your body isn't overworked with one discipline and works different energy systems and muscles to results in fitness gains across the board.

Nutritionist Amy Wood (ANutr), MSci BSc Nutrition has a keen interest in the relationship between diet and health. Having been published in the European Journal of Nutrition, Amy is passionate about making evidence-based nutrition accessible to everyone and helping others to adopt a food-focused approach to taking control of their health.