I decided to study personal training because, as fitness editor of WH, I rated myself as pretty clued up on the subject already and I wanted a piece of paper to make it official. Yup, the humility is strong with this one. Well, turns out, I wasn’t clued up. I got schooled. These were some of my lessons…

1. Rest is a much bigger deal than I thought.

In fact, it’s the most important part of your training programme. Human growth hormone (HGH) is the hormone your body pumps out to signal build and repair mode — i.e. #gains. It’s what prompts your body to beef up your muscles so they can cope with the workload they need to handle, a process that requires energy — hello fat burn. But here’s the thing – your body releases HGH when you’re sleeping. Imagine you owned a padstal and your home-made pies were flying off the shelves. Would you be making more pies while customers were queuing out the door of your shop? Nope. You’d replenish the stock at night when things were quiet and then sell ’em in the morning. Your body works the same way.

We’re going to need more crabby patties…

What’s more, those sexy sculpted muscles are the result of micro-tears in your muscle fibres that occur during exercise. When your body repairs the tears, it beefs up the fibres a bit in anticipation of the next hard training sesh. Now, if you’re skipping rest days and not sleeping, your body’s going to have no chance to rebuild. Your muscles fibres will break down and not be rebuilt and your energy stores will be depleted but never replenished. The result? You’ll be sick, tired and injured…and you won’t even have the sculpted body to show for it. Not cool.

Look familiar?

READ MORE: 7 Gym Hacks To Try If Your Wrists Hurt During Push-Ups

2. Don’t Forget The Second “I” In HIIT

When high-intensity interval training (HIIT) became a thing, I was all over it. I mean, cutting my gym time in half and still getting results? Hells yes! As I got fitter and up for more of a challenge, the interval part started shrinking until I just left it out altogether. HIT was where it was at… my body was a machine and machines don’t need to rest. Except, they kinda do.

You see, your body uses different energy systems depending on what kind of exercise you’re doing and what stage of your workout you’re in. When you’re doing moves that require a burst of energy (jumping; sprinting) or just starting your workout, you’re getting your energy from an anaerobic energy system that’s fuelled by creatine phosphate stored in the muscles themselves. But that creatine phosphate store is tiny and runs out after about 10 seconds.

Then another energy system kicks in that uses glycogen stores for energy. There’s plenty of glycogen to go round, but the catch here is that this system creates a by-product called lactic acid that causes you to become fatigued after about three minutes. The key to replenishing your creatine phosphate stores and overcoming muscle fatigue so you can go again? You guessed it — rest. That’s why even super-high-intensity exercise styles, like Tabata, have built-in rest periods. And if you’re worried about those Vitality points, during a short rest break, you’ll probably notice your heart rate climbing as your body works to replenish energy stores. Winning.

3. Don’t assume your trainer is clued up on diet.

I’ve had various trainers over the years and all of them have had something to say about my diet. That’s a good thing, because whether your goal is to lose weight, gain weight or just increase your fitness, diet plays a major role. That said, the average personal trainer is not a dietician. My personal training course was pretty comprehensive and there was a detailed module on nutrition. I’d feel comfortable calculating someone’s daily kilojoule requirements and giving them some pointers on how to clean up their diet. But let me reiterate that it was one module, compared to a whole degree that a dietician would have under her belt. If you’re looking for sound, detailed dietary advice, go see a specialist in the field.

READ MORE: Here’s How Increasing Your Core Strength Changes Your Body

4. Functional training is not the Holy Grail I thought it was.

Another trend I jumped on in a major way: functional training. No more restrictive movements and boring machines. The functional floor became my playroom and its equipment, my toys. My new workout philosophy was, “aim towards achieving a move and your body will find a way to get strong — or fit or bendy — enough to make it happen”. Well, there’s a catch — sometimes your body cheats. A prime example: Using the small muscles that are meant to stabilise your joints as “movers” when your big, “mover” muscles become fatigued. This is particularly common around complex joints like the shoulder. The result? Those little stabiliser muscles get overworked and, next thing, you’re injured and out of action. These days, my workouts are a balance of fun functional days that make me feel like a badass and old-fashioned, targeted strength exercises that help me build up the necessary muscles to perform my badass functional moves safely.

5. Understanding an exercise helps you do it better.

When you do a personal training course, you have to learn the biomechanics of exercise moves: what plane of motion the exercise takes place in, what joints and muscles are involved in different phases of the exercise and what happens at each. It’s very tedious. It’s also, in retrospect, very helpful. You see, when you know which muscles are meant to be working and what they’re meant to be doing, you know if you’re performing the exercises correctly or not. Which is important because…#gains. Next time your trainer shows you a new move, ask where you’re meant to be feeling it. You’ll pick it up much faster, minimise your injury risk and…get more #gains.