When you're in the training zone and really loving your workouts, it's tempting to skip rest days. After all, you're seeing great progress, your energy levels are through the roof and every session leaves you buzzing. More workouts can only be a good thing, right?

Not necessarily. Exercise, like most things in life, is all about balance. While it's great that you want to work out harder and more often, time out is a vital part of any exercise plan and even professional athletes schedule rest time and easy sessions into their weekly training.

"Rest days are massively underrated," says Jordane Zammit Tabona, Director and Lead Physio at Function360. "I see so many people with overuse injuries because they're training frequently and not taking enough time to rest. If you don't factor rest days into your training regimen, your performance can suffer, too," she warns.

Rest days allow your body - and your mind - time to recover from workouts. They stop you burning out and losing your mojo, and ensure you're ready and able to give your next session your all. Rest also gives your body time to adapt to your training and grow stronger and fitter, so you'll be better placed to make the next workout count than if you skip the recovery period.

In short, if you want to enjoy sustained progress, you're going to need to put your feet up every now and again. But how many rest days should you take, what are the benefits and do you need to spend all day on the sofa with the remote?

Here's everything you need to know about rest and recovery.

5 reasons why you should take a rest day

1. They help you get stronger

While you may think fitness gains are only made when you're beasting yourself during a sweat session, rest is just as important if you want to hit your workout goals.

"Muscle is developed in its 'repair phase', when you're resting and refuelling," says Jordane.

Every time you work out you create microscopic tears in your muscle tissues. When you rest, your muscles start to heal and grow back stronger, meaning you'll be able to do the same workout with less effort in the future.

2. They help you avoid injury

If you skip rest days, it could lead to longer spells out through injury. Working out when your body and mind are tired means you're more likely to have bad form, trip or stumble. You're also at risk of overuse injuries as you constantly stress and strain the body and don't allow it the necessary time to repair itself.

"Increasing the amount of training you're doing or upping the intensity, without giving your body enough time to rest and recover, is a common cause of injuries like stress fractures and tendinopathies," says Jordane. A recent study found that overuse injuries were the most common types of injury in elite athletics, leading to at least three weeks out of training for affected athletes.

So if you want to avoid weeks or even months of being unable to train, make sure you give yourself sufficient time to rest.

3. They help you make fitness progress

Train too much without resting and you could see your fitness progress grind to a halt or even go into reverse. Exercise releases stress hormones and, just as working long hours with no days off can negatively impact your health, too much exercise without enough rest can lead to burnout.

Also known as overtraining syndrome, burning out can affect your central nervous system, throwing everything out of whack. Your central nervous system is made up of different parts including the sympathetic nervous system - which triggers fight or flight mode - and the parasympathetic nervous system, which helps calm your body down again. If you're not taking the time you need to rest and recover, then the constant stress of exercise can mess with your system's natural responses.

This can leave you feeling constantly tired and drained. Workouts can feel much harder than they used to and you may struggle to do exercises you found fairly straightforward before.

4. They mean you can train even harder

We all know that feeling. You've just finished 30 seconds of flat-out exercise in your HIIT session and swear you couldn't do another evil burpee again, ever. Then, just 20 seconds later, you're ready to go hard and attack it again.

That's what rest days are like. Taking time off gives your body and mind time to reset, recharge and recover. Your muscles will be less sore and fatigued and, instead of just going through the motions, you'll be able to give your next workout the effort it needs to get results.

Studies have shown a lack of sleep can result in low motivation to take part in leisure activities you usually enjoy, and failing to take mental breaks to recover from exercise can have a similar effect. Mini breaks keep your motivation running on overdrive, preventing exercise from becoming a chore. Absence makes the mojo grow stronger.

5. They help you build long-term habits

A survey of over 2,000 people found that 33 per cent who don't exercise say it's because they don't have the time. While we all know how easy it is to fit a HIIT session into your daily routine, that becomes much harder, logistically and psychologically, if you're trying to do it every day of the week.

Rest days help make your schedule more flexible, leaving you to build workouts around your life rather than vice versa. Having that flexibility can also make your workout regime more sustainable - if you are unable to workout one day, then you can swap it for your rest day and complete your workout later in the week without compromising your training. This helps you build healthy habits you can keep up for life, too.

How many rest days do you need each week?

The number of rest days each person needs varies. It can depend on a variety of factors including the duration of your workouts, your current fitness level, goals, age and genetics.

"Everybody's different and some people just need more rest than others," says Jordane. "Generally speaking though, the more intense the training sessions, the more rest the body needs. Things like the time of the month and the menstrual cycle can affect some women, too."

During your period, progesterone and estrogen are at their lowest levels. This can make some people feel more tired than usual. While it's fine to exercise when your energy levels are low, sometimes a rest day may do you more good so you can recharge, ready to give your next workout everything you've got.

Jordane advises taking up to three rest days a week if you're exercising for general health and wellbeing. If you are new to exercise, you may want to take more as you gradually increase the frequency of your workouts.

You can also build more rest into your training by scheduling easier workouts for the days following tougher sessions, so you're not at risk of overdoing it. If you're strength training, alternating between upper and lower body also gives your muscles extra time to recover.

What should you do on rest days?

Rest days don't have to be spent zoning out with a boxset. Active recovery - that's very gentle, low-impact exercise - can be beneficial, too.

Walking the dog, playing with your kids in the park, stretching and self-massage with a tool like a foam roller can all get the blood flowing and help you relax.

Rest days are also the perfect time to give your mind a break so you feel refreshed for your next workout. Enjoy the freedom of not having to think about exercising. Try meditating - apps like Headspace have some great guided meditations if you're not sure where to start - or take a long bath with some relaxing music and a good book.

"Rest days are super important to your overall health and wellbeing," say Joe. "On days when I'm not training, I like to stay active and go for a nice walk. Being outside in nature is really calming and I always feel good afterwards."

It's important to ensure you're getting some quality sleep, too, as the hormones that help repair your muscles are released during sleep. "Sleep is one of the most underrated factors in terms of our health and happiness," says Joe. "This year I'm really focussing on improving my sleep." Sleep and mental health go hand in hand.

If you're not sure whether to rest or whether to train, listen to your body.

"Ask yourself, do you want an extra rest day because you're feeling lazy, or do you need an extra rest day because you're taking longer than usual to recover?" says Jordane. "If it's the latter, you'll benefit from taking the extra rest. You can always train harder the following day."

Jordane also advises taking extra rest and consulting a specialist if you suspect you're carrying an injury. This is usually a specific site of pain that doesn't seem to ease off.

Written by freelance writer Charlotte Thomas.