The first thing to change is the blood. Within about two weeks of regular running your plasma volume rises, your heart fills a little more with every beat, and the same easy pace costs a few fewer heartbeats. You haven't built anything yet. But it's the first proof the body is listening, and it arrives before you'd notice in a race.

The next two to five months are the engine. Capillaries grow into the muscle, mitochondria multiply, and the big number, VO2 max, climbs. In the largest study of it, the HERITAGE Family Study, sedentary adults did twenty weeks of supervised training and gained about 400 millilitres of oxygen a minute on average. The spread was enormous: some people barely moved and some gained more than a litre. Same programme. If your friend is improving twice as fast as you, that's normal, and it says nothing about where either of you ends up.

Then the easy gains stop, and this is where most people decide they've peaked. They haven't. What improves after the first year is economy: how much oxygen each stride costs. It's slower and it barely shows on a watch from month to month. Paula Radcliffe's physiologist tested her from 1992 to 2003. Her VO2 max hardly changed in eleven years. Her running economy improved by fifteen percent, and she took the marathon world record to 2:15:25.

The parts that hold you together are slowest of all. Tendons and bones remodel over months and years, far behind the heart and lungs, which is why the runner who feels fit after ten weeks and doubles the mileage is the one who gets hurt. The engine is ready before the chassis. Every sensible plan is built around that gap.

So: a few weeks to feel different, a season to get fit, a year to find out what kind of runner you are, and somewhere between seven and ten years of steady training before you stop getting better. That last number is the good news. It means the runner you'll be in five years isn't visible yet, to anyone, including you.

Every runner knows they should do strength work, and most don't, because it means a second session, a gym, and a plan. So start with the version that removes every excuse: you've just finished a run, you're already warm, and the ground is right there.

What does the evidence say? The best-known study of core work in runners took 28 recreational runners with 5K times just under 30 minutes. Half added core training for six weeks. They improved their 5,000 metre time by 47 seconds on average; the group that only ran improved by 17. It's a small study, and it didn't find any change in how they ran, so nobody can tell you exactly why it helped. But they got faster.

Be honest about the ceiling. The big, well-proven gains from strength training, running economy improving by two to eight percent in a 2018 review of the research, come mostly from heavy lifting and jumping with the legs. Push-ups and sit-ups aren't that. What they do is train the parts that give out late: the shoulders that creep up toward your ears at mile ten, the middle that folds when you're tired.

The reason to do it after every other run, and not every run, is that it stays easy to say yes to. Three or four short sessions a week, attached to something you already do, beats one heroic gym day you skip by March.

Stop each set two reps before you'd fail. Add a rep a week. When three sets of twenty push-ups is easy, slow them down before you add more. That's the whole method.

When you run hard, your muscles produce acid faster than they can clear it, and that burn is part of what makes you slow down. Sodium bicarbonate raises the blood's capacity to soak that acid up. More buffer, a little more time at full effort. That's all it is.

The science isn't new or thin. The International Society of Sports Nutrition's position paper puts the effective dose at 0.2 to 0.5 grams per kilo of bodyweight, with 0.3 the sweet spot, taken 60 to 180 minutes before the effort, with at least half a litre of water. The benefit shows up in high-intensity efforts lasting between 30 seconds and 12 minutes.

So why the craze now? Because the old way of taking it was a gamble. Swallow that much baking soda and a good share of athletes got cramps, bloating or worse, sometimes mid-race. What changed is the packaging: Maurten's Bicarb System wraps it in a gel designed to get it through the stomach before it reacts. Elite milers and 5,000 metre runners took it up, people noticed, and now it's on every start line. It costs about $70 for four servings.

Do the arithmetic before you try it. For a 70 kilo runner, 0.3 grams per kilo is 21 grams of sodium bicarbonate, which carries nearly six grams of sodium. The usual advice is to stay under 2.3 grams of sodium in a whole day. If you have high blood pressure, kidney problems, or you've been told to watch your salt, this isn't for you, and it's worth asking a doctor either way.

And be honest about the event. If your race is a marathon or a half, the limiter isn't acid, and the paper's own time window ends at twelve minutes. For most of us the gains on offer are still the boring ones: more easy miles, more sleep, and eating enough.