Cardio is like marmite, you either love it or you hate it.

We tend to find two kinds of trainers, those who love nothing more than to lace up and head out for their runner's high for as long as they can and those who talk themselves into 20 minutes of cardio by breaking it down into 4 sets of 15 minutes, counting down from about 4 minutes in.

Cardio Training

Low Intensity Cardio

Low Intensity cardio is easy and everyone can and should, do it. Low intensity cardio exercises include walking or a light cycle. These kind of exercises are low impact and typically performed around 40% of your maximum heart rate, which make them easy to recover from and therefore can be performed on a regular basis.

Benefits of Low Intensity Cardio:

  1. Burn extra calories. Whilst the exercise is not intensive, moving more burns more calories and prevents from the dangers of sitting. Low intensity exercise can help to burn more calories and maintain weight.
  2. Low intensity build muscular endurance. Low intensity exercise builds muscular endurance, as the body effectively performs lots of easy reps over a long period of time.
  3. Low intensity cardio controls appetite. Psychologically, where we’ve not been physically worked so hard from low intensity cardio, we don’t feel the need to re-feed. Research from The American Journal of Physiology: Regulatory, Integrative and Comparative Physiology suggests that long sessions of low intensity inhibit hunger hormones. The study found that 60 minutes cardio increased the release of an appetite suppressing hormone and decreased the release of a hormone that promotes hunger.

Moderate Intensity Cardio

This is often referred to as steady state cardio, it's the kind of cardio where you're going for a steady run, swim or 40 minute session on the elliptical. If you’re an endurance athlete, or runner, this is your golden zone. Typically you will be working at about 60-80% of your maximum heart rate.

Benefits of Medium Intensity Cardio:

  1. Enhances your aerobic system. Our aerobic systems fuel most of our day to day physical functions, from breathing to our digestive system. Aerobic energy (energy created with oxygen) is present in everything we do, so improving your aerobic engine will improve everything else.
  2. At moderate intensity the left ventricle of the heart has time to fill and contract, developing an increased capacity, pumping more blood with each contraction (over time), lowering your resting heart rate.
  3. Maintain muscle mass. Moderate cardio burns mainly carbohydrates and therefore maintains muscle mass, however, if you run out of alternative fuel sources, eventually your body will turn to your muscle stores for energy.
  4. Medium recovery time. Medium intensity workouts require medium amount of recovery.
  5. Manage diabetes. This level of intensity of exercise helps the body to burn glucose, and regulate blood sugar levels.Those who exercise regularly tend to have better control of their blood sugars and do not see as many blood sugar swings as those who don't.

High Intensity Cardio

High- Intensity cardio is the kind that leaves your heart in your throat. It’s the full pelt on the treadmill, flat out throwing of battle ropes or boxing like you’re the next Balboa. High intensity exercise now boasts its the best for torching fat and calories.The sheer intensity of the exercise is what causes the extra calorie burning, not at the time, but in order for your body to recover.

Benefits of High Intensity Cardio:

  1. Boosts Metabolism for up to 24 hours. High intensity interval training causes an increased need for oxygen, we therefore continue to burn calories EPOC, excess post exercise oxygen consumption.
  2. Increased VO2 max. Your VO2 max is the maximum amount of Oxygen your body can uptake at any one time and is a good judge for your level of fitness. A higher VO2 max means you can perform and recover faster.
  3. High-intensity exercise can burn quite a bit more calories than low-intensity exercise, and as fat loss is dictated by energy balance, the advantage here is clear.
  4. Shorter workouts are great for those who lack a lot of free time to train.
  5. Increased Lactate Threshold. Your ability to handle increased lactic acid buildup in your muscles increases.
  6. Anabolic. For those looking to build muscle, interval training combined with a calorie surplus has been shown in some studies to have an anabolic effect, helping to build muscle.

The big arguments against cardio:

It’s: a) too hard, b) boring, c) I’m no good at it.

A, b, c or all of the above, aren’t really arguments against cardio are they? More like excuses. Let’s target them one by one.

  1. It’s too hard. Every exercise is going to be hard at some point, when you’ve never done it before, cardio can be difficult, but stick it out and it does get better. Your body is very clever, it adapts and improves, within weeks it will start to get easier, you’ll be able to notice a difference and that can be very motivating. The beginning is always the hardest.
  2. It’s boring. Your cardio is only as boring as the person who designed it. Cardio doesn’t have to be sat on a stationary bike, it could be boxing, kettlebells, battle ropes or plyometrics. Get creative with your cardio and find something you enjoy, think outside the box a little and your cardio won’t stay boring. Tip: If you’re really stuck for ideas, pop into a class such as spin, the instructor will do all the planning for you - all you’ve got to do is go for it!
  3. I’m no good at it. If we always did the things we were good at, we’d never learn anything new, would we? Whilst some people may be more naturally built for cardio, if you work at it, you can be too. Remember: Hard work beats talent when talent doesn’t work hard.

Muscle loss

Broscience will have you believe that cardio will kill your gains, but is there really any research in it? There is research to support cardio and there is research against it.


Cardio decreases recovery times. Intense activity causes damage to muscle fibers, these then repair and grow bigger and stronger. Two factors which affect the rate at which these repairs take place are how much of the substances needed to induce repair are brought to the muscle over time and how quickly waste products are removed.

Cardio increases blood flow, which can help your muscles to repair quicker by speeding up these two processes. The faster you repair, the faster you can train again and work on your “gains”.

HIIT training can help you gain muscle: The Journal of Strength and Conditioning Research published research suggesting that HIIT can actually increase testosterone levels. Testosterone is a muscle building hormone.HIIT also sets off an increase in the concentration of myofibrillar nuclei. Hypertrophy depends on increases in this concentration, along with the content of your muscle fibers.


Prolonged cardio increases cortisol levels. Too much cardiovascular exercise will cause Cortisol levels to increase and Cortisol will eat away at your muscle fibres and reverse the effects of your muscle building training. After around an hour of training, testosterone levels drop and Cortisol levels rise, preventing muscle growth.

When you’re trying to build muscle, you need excess calories. Cardio burns calories, which can end up putting you in a deficit. Whilst for weight loss, this is exactly what’s needed, when trying to bulk up this could lead you to go catabolic.

Cardio and Muscle Building

Whilst there are arguments for and against cardio when trying to gain muscle mass, a lot of the results will depend on the individual, as everybody is different. In order to maintain health, we would never recommend excluding cardio completely, however to gain muscle mass, cardio needs to be maintained with a calorie surplus. Low intensity sessions of between 20 - 40 minutes can be used on rest days or post workout to aid recovery whilst HIIT training may be implemented twice per week as part of a muscle building routine, if fueled correctly and can actually promote further muscle growth. For muscle gain try to aim for 2-3 cardio sessions per week.

The type of cardio you should do will depend greatly upon your goal.

Cardio and Weight Loss

The biggest rule of weight loss is calories in has to equal less than calories out, however cardio can be implemented into a training regime to assist weight loss. Cardio for weight loss is often a long debated subject, is high intensity better or should we work specifically in our ‘fat burning’ moderate intensity zones. Why pick one or the other, why not both?

For our bodies to change the most we have to keep stimulating your muscles differently, so combining a mixture of HIIT and steady cardio can be great for weight loss. Whilst HIIT will burn more calories after the exercise is finished, steady state cardio still burns a chunk of calories and is easier to recover from.

Mixing HIIT and moderate cardio such as swimming or jogging will train both the aerobic and anaerobic system to build a good level of fitness as well as assist in a weight loss regime , providing you burn more than you eat.

With any form of activity, if there is no other fuel source, your body will eat at its muscle mass.

Cardio for event training / athlete

A person training for a 10k will usually implement all three types of cardio in their routine, to challenge their different energy systems and build strength in all areas. Despite the 10k being steady state cardio, training would involve low intensity, moderate and HIIT cardio. For example a person may complete 4-5 sessions a week:

Day 1 complete light cardio, 40 minutes, jog. Day 2 high intensity cardio, HIIT 20 minutes sprints. Rest on day 3, complete further light cardio on day 4, HIIT on day 5, rest on day 6, followed by an endurance run on day 7, where you would run to near the distance of the event.

As well as doing cardio that is specific to your goal, it’s important to find a form of cardio which you love, or at least like. If you really hate the cardio you’re putting yourself through, you just won’t keep it up.