I don't need a scientist, a personal trainer, or a celebrity to tell me that I feel better when I exercise. I know I do. I have more energy and enthusiasm. I'm less likely to reach for a chocolate biscuit and more likely to run around with my kids.
Of course, it seems faintly ironic that expending energy leaves you more energised, but this is clearly the way it works.
What is definitely ironic is that a group of people who are most in need of an energy boost – those with young children – are least likely to have the time to exercise.
Even Michelle Bridges, mother to 6-month old Axel, is struggling to find the time and energy to keep up with her (admittedly full on) exercise regime.
So spare a thought for those with more than one child, or a more needy child, or without a good history of exercise.
When my second child was at a similar age to baby Axel, I was doing to no exercise. Nothing. Nada. Zero. I was constantly exhausted – from lack of sleep, as well as the physical effort of looking after a needy toddler and a baby (in addition to a house and, very occasionally, myself).
I was in energy-conservation mode, focussed on expending as little energy as possible, just to get me through the day. I just didn't have enough energy to invest in the activity I needed to help me feel better.
A glimmer of possibility arrived when my baby was a year old, when a 30-minute gym opened smack bang in-between work and home. "Surely I can manage this," I thought.
I rang and spoke with the very kind owner of the gym, who answered my questions about their opening hours and assured me that they really did that I could be in and out within 30 minutes (not a 30-minute workout plus 15 minutes either end for warming up/cooling down/waiting around).
I then started trying to work out, aloud, when I could attend. Speaking to that kind lady, I outlined my work hours as well as those of my husband. I explained how I needed to be home at certain times due to breastfeeding, and discussed how the idea of getting up 'an hour earlier than usual' to exercise doesn't really work when you're functioning on as little sleep as I was.
In the end, it was she – the owner of the brand new gym who was presumably desperate for new members – who said it: "I don't think you can fit this in right now."
And she was right. I couldn't.
I tell this story with hindsight, so I now know that this situation didn't last forever. Exercise was able to come back onto my agenda a year or so after this point.
At that time, though, I had no option but to accept that no matter how beneficial some exercise would have been, it just wasn't possible for me right then.
Of course this isn't the case for all mothers of young children. Some have less-demanding children, more extended family support, partners who work shorter hours, the ability to function on less sleep, or jobs where a 30-minute walk at lunchtime is possible.
But this was the case for me, and I therefore know that sometimes, there are excuses – good ones – and that the good old 'Just Do It' slogan just doesn't cut it.