Couch to 5K
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How does it work?

I'm interested in a little bit of science here.

How does getting fitter, building stronger muscles work?

Does it really work that you do a session, have a rest day then can magically do a bit more the next time (factoring in that this is not necessarily constant but that there will be days when you can do a lot less).

It looks like an awfully steep learning curve but I'm assured that it's not actually so hard that most people who start can't finish within maybe 2 or 3 weeks of the projected 9 week plan.

4 Replies

It take months to build muscle. c25k improves stamina and fitness by encouraging you to exercise vigorously for 30-40 minutes. Many people plan to go out 3 times a wek and then take weekends off, perhaps. It's best to fit it in to your lifestyle and not be too rigid about going out every other day or you might not keep it up. Each run for the first four weeks is done 3 times. it's not necessary to repeat weeks unless you failed to complete the runs and the important thing is to go at a pace which is comfortable and sustainable for you. You might have to slow down to complete the long runs, but that's OK.

It does look challenging- and it is, but as each week presents a new challenge, so your body responds. It really does happen, so have faith in yourself and the programme!

Good luck :)

Reply if it takes months to build muscle I'm wondering how in a few weeks my legs get strong enough to keep going for longer at a time.


honestly, you don't need really muscular legs to run. Start on a flat route with soft ground ( canal towpath, treadmill, woodland path, park after rain) and that will reduce strain on your muscles. You will build up the stamina to keep going.


As happierswimming says, you don't need huge 'King/Queen-of-the-Mountain' (Tour de France-style) size muscles to plod along for 30 mins. Look at any competitive distance runners.

So how does this 'run-a-day-rest-a-day' work? It's not quite magic ;-)

The science behind it:

Your body builds muscle naturally in response to strenuous activity. Muscles grow during rest, not during training. When you run, by pushing yourself a little, you stress the muscle to the extent that it breaks down at the cellular level, resulting in increased protein synthesis, which produces thicker muscle fibres. This process begins 2-4 hours after the workout and lasts about 24 hours. If you don't give a muscle adequate time to recover, then you'll actually interfere with the muscle building process and can end up injuring yourself.Hence the suggested rest day for us beginner runners.


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