So this is why some days you can’t drag yourself to the gym

Ever wondered why some mornings you can squat, skip and sculpt like a Victoria’s Secret model, and others you’d rather commit to giving up cheese – forever – than do a sole ab crunch?

Well, no need to be so hard on yourself. Turns out it comes down to your physiology, not fitness levels. And specifically: your menstrual cycle.

According to environmental exercise physiologist Stacy Sims, the hormonal changes your body goes through each month have a major impact on your energy levels – and, as reported on Refinery29, which type of workout will best sync up with your cycle.

And here’s where it gets interesting. While many of us believe that “that time of the month” gives us license to nestle into the couch with a lifetime's supply of chocolate and Netflix, this is actually the week when our bodies are primed for high-intensity training. Yep, you read that right.

Jen, we got you. Herewith, a period-approved workout schedule … *

Week 1 (the period bit)

Your oestrogen and progesterone levels are at an all-time low, but glycogen (your fuel reserve) is readily available. If you can beat an initial energy slump or cramps, you’ll run faster and hit PB-crushing intensities. Schedule some cardio stat.

Week 2 (the happy post-period bit)

Your oestrogen and progesterone are on the rise, but still low. In short, this is when your body is kind of like a man’s. The upshot? You’ll pump iron like a boss, so focus on strength training.

Week 3 (the bit when you ovulate)

Oestrogen levels – along with your energy – will tank. Stick to lower-intensity workouts or floor-based classes such as barre or Pilates.

Week 4 (the premenstrual bit)

As your body preps for your period, progesterone soars – though your mood and motivation will probably do the opposite. Try gentle indoor cycling or yoga to get your mojo back.

*The disclaimer bit: every body is different, so listen to yours (except when it tells sneaky lies about chips).