The Rest Is History: Science to help you return to exercise in September
By Rory Girvan 5-7 minutes
January aside, September is the only time of year when picking back up where you left off, or starting afresh, tends to come naturally. But whether that’s the faint feeling of seasonal change in the air, the schools starting back, or the summer drawing to a close is by-the-by. The main thing is that for anyone who’s been inconsistent or taken a break in recent months, it’s an opportunity to get back on track with exercise and healthy habits.
How Routines Break
A week off for a holiday becomes three. Three weeks can become the summer. Between trips away, family visiting and a welcome stretch of good weather, changes in routine just happen, without it ever feeling like a decision.
If you’re starting back, the thought of picking up where you left off might be equal parts excitement and trepidation. The latter comes with the territory: the sense that you’ve undone everything, that you’re starting from scratch, and the reflex to compare yourself with how you felt, looked or performed before.
But here’s the great news. From a physiological standpoint, your body is in a much better position than you think.
What Goes and When
Some won’t have stopped altogether, just exercised less. If that applies to you, try reframing those months as a maintenance period rather than a developmental one. Instead of feeling like your progress stalled, give yourself credit for retaining the foundation needed for the months ahead.
And if you stopped completely for a fortnight, a month or longer — the science is on your side. However, it plays out differently for strength and aerobic fitness as they don’t fade, or recover, at the same rate.
The Durable One: Strength
A fortnight off costs nothing worth measuring. There’s no meaningful loss of the contractile muscle tissue that does the actual work, and with accumulated fatigue finally cleared, plenty of people come back feeling fresher than when they left. A month does cost a bit more, but mostly in coordination rather than muscle — your nervous system’s ability to recruit the muscle you still have, which returns within a few sessions of lifting ‘practice’. A few months is more significant, though still modest, with maximal strength holding up better than muscle size.
The Perishable One: Aerobic Fitness
This one fades sooner, but the part that fades first is also the part that returns fastest. In trained endurance athletes, maximal oxygen uptake (VO2 max) can fall around 5% inside a fortnight — but that initial drop is driven mainly by falling blood and plasma volume, not by the heart, capillaries and mitochondria, which take far longer to fade. Plasma volume rebuilds quickly once you start again.
Similarly in muscle, much of what looks like lost size in the early weeks is stored water and glycogen: the carbohydrate your muscles keep in reserve, rather than muscle protein. In the cardiovascular system, it’s blood volume. In both cases the fast loss is fluid, not the actual hardware. This takes far longer to build, and far longer to lose.
‘Starting Over’ Doesn’t Feature
It almost never does. In almost two decades of strength coaching I’ve yet to meet anyone who came back from a layoff and was genuinely at square one — which is also in line with the evidence base for this. In a 2024 study in the Scandinavian Journal of Medicine & Science in Sports, adults who stopped completely for ten weeks were back where they’d left off within five weeks of returning, and finished level with those who trained straight through.
One perhaps sobering caveat. Short spells of inactivity really can cost the equivalent of years of natural ageing, but this applies in cases of illness, injury and bed rest, where the body is completely unloaded and devoting its finite resources to recovery. For otherwise healthy people, the summer months usually still involve time outdoors — walking, carrying luggage through airports, or just keeping up with indefatigable young family members.
What You Need to Know
A fortnight off costs little worth measuring; a month is mostly lost ‘practice’, not lost muscle
Aerobic fitness fades faster than strength, but the part that goes first – blood volume – comes back quickest
The first session back should be strategically easy, and ideally, fun
Back on Purpose
The first session has only one job: to get moving, work up a sweat, and enjoy getting back on the horse. So the plan is simple, and the dose is smaller than you’d think.
For lifting: take about a third off whatever you were using, and do roughly half the volume you think you can handle.
For running, cycling, hiking: go back at about half the distance, and keep the effort easy enough to hold a conversation.
Either way, build back gradually over the course of a few weeks.
It should feel too easy. But it will still be enough to switch on the adaptations you’re after, without the days of soreness that follow going too hard too soon that may quietly talk you out of the next session.
The hardest part is reinitiating the habit so getting the logistics sorted is key. This means booking the time in your diary to exercise, getting your gear out the night before, then turning up. The rest will look after itself.
The purpose of restarting isn’t just to start another training block, new programme or personal challenge. It’s to embed anchor habits that support your overall health, life and relationships — all for the better. And, other than the obvious, there’s no better time of year than in September to make make the rest history, and get started today.
Written by Rory Girvan BSc (Hons), AdvDip PN — Founder
Rory holds honours degrees in Biomedical Science and Sport & Exercise Sciences and an Advanced Diploma in Nutrition Coaching. A former IPF Powerlifting champion (NI, Ireland & All‑Ireland) and Irish Open weightlifting winner, he also earned silver at the Drug‑Free World Powerlifting Championships. Inspired by his own 70 lb weight‑loss transformation, Rory combines evidence‑based strength training with mental‑health advocacy — as seen in his role as fitness columnist for The Irish News — to develop the HENCH methodology that helps members build lifelong resilience.