Hamstring cramping.

[roobab]

I have a consistent problem , when I ride more then 70k , say approaching 100k, my left hamstring starts to cramp badly at the end.
Today, it got so bad, I had to unclip and just use my quads.

[greyhoundtom]

From my experience a past injury that has left a specific muscle with some minor scar tissue or an impaired blood supply, will cause that muscle to cramp and fatigue sooner. Massage with heat producing liniments and more stretching may help, or ultrasound treatments if a specific area of injury can be identified.

It may also help if you move your saddle forward 3 cm and that will make you use your quads more than hamstrings and glutes, and so take the strain off the hamstrings.

[eeksll]

I have no idea of your training so i am probably be way off base, but on longer rides and my quads get tired I start to actively think about doing the full circle thing when pedalling and this makes me overuse my hamstrings which can cause them to start to cramp.

[/\ |_ |]

To answer this question we need more info such as; how often do you ride and what distances during the week? Are you doing 70km+ every week or once a month? Do you drink plenty of water on your ride? Good way to work out if you are drinking enough is to weight yourself before a ride and than after. If you are lighter than your start weight the difference what you should have drunk on the road. Say the difference is 1kg than you need to drink 1L more on your ride. Have you been properly fitted to your bike? This will make a big difference to your bike handling and pedaling efficiency.

[goneriding]

magnesium might do the trick. I find that, during Summer, I get cramps whilst stretching post ride. Taking magnesium tablets helps with this.

During the ride try bananas as they have plenty of magnesium in them.

It might also have something to do with your fit. If you are starting to do those kind of distances it is probably worthwhile to prevent any longer term injury.

[roobab]

I ride at least 150k a week. Bike fit is good. Sounds like the problem is not enough water.
Question is, why only left hamstring cramping?

[rustychisel]

Question is, why only left hamstring cramping?

Ans: how long is a piece of [ham]string?

Could be a functional disability, an old injury, most likely associated with you not being entirely centred on the bike, thus favouring one side over the other, or being dominant on one side and doing more work that side, or a tendon related issue where you're 'pulling' and scrunching the muscles of the left leg, thus irritating or tightening the hamstring, or your pelvis is misaligned, or it's none of those things at all.