Knee discomfort on turbo trainer

[peterh11]

Hi all,

What with self-isolation, I got the turbo trainer out of the shed a few days ago, and started doing a short session every day to replace my commute to work. I'm noticing some discomfort in my right knee which had big problems about 7 years ago (sorted with help from a lot of physio to improve various aspects of strength and flexibility). Normally I can ride out with my CTC Cambridge clubmates for a half day ride, or indeed go for a whole day with some breaks, with no knee (or other) discomfort at all. We are not a high speed club - maybe 35-40km in a 2 hour run to a cafe and then the same back is a typical ride speed, and I can do that on either of my touring bikes no problem.

The turbo trainer is a classic type with a wheel which runs against the bike’s rear wheel with constant magnetic resistance. It has an adjuster with 5 settings for resistance level.

I do notice that riding on the trainer is quite different from normal riding. It seems to me that there is a constant load on the pedals/cranks rather like climbing a hill or riding into a strong headwind. If I stop pedalling even in the lowest resistance setting of 5, the back wheel stops within a few seconds, whereas if I stop pedalling on a relatively flat road, the bike will coast for quite a while. So there is a constant drag on the pedals which is not there in steady speed road riding.

I searched round the internet and found a few theories for the issue such as the frame being held rigid, but I think for me it is about the type and amount of loading. Have others experienced the same, or can anyone provide some scientific explanations for this?

My hypothesis is that it is this constant pedalling against resistance which is the issue. In a normal ride on a road the loads would vary constantly with even minor variations of gradient up and down hill. I'm going to try switching to what feels like a very low gear for warming up, then vary the gear to simulate changes from super low (no effort) to moderate, all the time pedalling with intensity which feels "too little". Also, I will keep the session short - even outside in the garden with music or podcast it gets boring! Does this make sense?

PeterH

[531colin]

I think its worth doing your prescribed physio. exercises from your previous problem; I think I would try doing that in conjunction with making your turbo sessions short and varying the intensity, as you say.

[thatsnotmyname]

I do notice that riding on the trainer is quite different from normal riding. It seems to me that there is a constant load on the pedals/cranks rather like climbing a hill or riding into a strong headwind. If I stop pedalling even in the lowest resistance setting of 5, the back wheel stops within a few seconds, whereas if I stop pedalling on a relatively flat road, the bike will coast for quite a while. So there is a constant drag on the pedals which is not there in steady speed road riding.

This may or may not be related to your knee issue, but it does sound as though you have the roller pressure adjusted slightly high. Roller pressure tends to be a separate control from resistance on most mag turbos. If there is any method of reducing the roller pressure on the rear wheel, it might be worth trying that in order to give you a little more in terms of roll-down. Depends on what you are defining as 'a few seconds', but you would generally expect the rear wheel to spin down from a typical road speed for a little longer than that.

[peterh11]

I think its worth doing your prescribed physio. exercises from your previous problem; I think I would try doing that in conjunction with making your turbo sessions short and varying the intensity, as you say.

Thanks, but I do already. I collected a set of exercises from several physios which address flexibility in mainly hamstrings, calves and glutes, and strengthen the various stability muscles around and above the knees. Includes classic stretches as well as squats both single leg and with both legs. I still do them a few times per week which I think has made a huge difference to my ability to ride multiple hours on the road at moderate speeds. Big differences from before the injury are that I can easily ride with my feet aligned fore-aft with toes NOT pointing out, and I can more comfortably use the drops for a while. I also (normally) go to the gym every week.

The single leg squats are what has made the biggest difference, I recommend these as part of a programme (but be VERY cautious and check with a professional if any pre-existing conditions - start with two legs then just a few single leg at a time, standing in a doorway until you can balance) as they help with balance, strength and flexibility.

I experimented this morning and I think this is to do with the fact that even on minimum resistance this trainer setup is equivalent to going uphill and so I have simply been overdoing it! Will make a new post with more observations.

PeterH

[peterh11]

I do notice that riding on the trainer is quite different from normal riding. It seems to me that there is a constant load on the pedals/cranks rather like climbing a hill or riding into a strong headwind. If I stop pedalling even in the lowest resistance setting of 5, the back wheel stops within a few seconds, whereas if I stop pedalling on a relatively flat road, the bike will coast for quite a while. So there is a constant drag on the pedals which is not there in steady speed road riding.

This may or may not be related to your knee issue, but it does sound as though you have the roller pressure adjusted slightly high. Roller pressure tends to be a separate control from resistance on most mag turbos. If there is any method of reducing the roller pressure on the rear wheel, it might be worth trying that in order to give you a little more in terms of roll-down. Depends on what you are defining as 'a few seconds', but you would generally expect the rear wheel to spin down from a typical road speed for a little longer than that.

Interesting. Thanks for mentioning this. I had a good look at the trainer (it is an Elite Volare Mag which I bought in 2015). There is no way to adjust roller pressure except for switching between two mounting positions - pretty sure this is meant for switching between 700C and 26" wheels, and I have it on the right position for 700C.

The roller's position when disengaged is very close to the tyre. It looks to me as if the device is really designed for 25 or 28mm tyres - and both my tourers have 37mm Schwalbe Marathon Supreme tyres. This may result in more pressure on the tyre than intended. I may buy a cheap 28mm tyre to experiment and save wear on the nice tyre if I have to carry on doing this (smallest I think I can reasonably fit on the Exal LX17 rim). I did check tyre pressure: I have it pumped up above 5bar and the deformation from the roller pressure is pretty small.

I tried out the lowest resistance setting and some different gears on the bike this morning. My impression is that pedalling in about 2 gears lower than I usually would on the flat when riding at steady speed feels about the same pressure on the pedals. It takes about 6-7 seconds to come to a standstill from ~20kph (estimated from gear and cadence) which is quite quick - very roughly 10m if it were on the road and therefore similar to moderate upward slope or braking.

Right now I will go cautiously, remembering that my mind wants me to pedal harder than I should, probably because I am used to doing pretty high intensity work on a rowing machine in the gym which of course has quite a different knee loading pattern - warm up with an easy gear and then do intervals including a bit of freewheeling and paying careful attention to how much pressure I am putting on the pedals. Maybe I will even benefit from some improved strength by doing that

Hope this thread might be interesting and useful to someone.

All the best
PeterH

[thatsnotmyname]

The roller's position when disengaged is very close to the tyre. It looks to me as if the device is really designed for 25 or 28mm tyres - and both my tourers have 37mm Schwalbe Marathon Supreme tyres. This may result in more pressure on the tyre than intended. I may buy a cheap 28mm tyre to experiment and save wear on the nice tyre if I have to carry on doing this (smallest I think I can reasonably fit on the Exal LX17 rim). I did check tyre pressure: I have it pumped up above 5bar and the deformation from the roller pressure is pretty small.

I suspect the size of the 37mm tyre is having the effect of putting higher than expected pressure on the roller, so more friction. Definitely consider changing tyres, but I'd be looking for 23-25mm ideally..

[531colin]

On a turbo, it may be OK to fit an "undersized" tyre. You will get a somewhat flattened tyre profile which would leave you open to pinch flats on the road; but I guess you don't get pinch flats on a turbo?

[peterh11]

Further thoughts on this - maybe I am only talking to myself

(I've just taken delivery of a 28C tyre which I will put in this weekend, and see how that changes the behaviour.)

Now that I have had half a dozen sessions or so, and had a quick search around the internet, I observe:

Since the bike is firmly clamped to the trainer, my effort is concentrated much more strongly in the muscles which turn the pedals, in contrast to when I am riding on the road when a lot of other muscles in torso, arms, neck etc are engaged. This also (I think) has the effect that the muscles engaged when pedalling are not exactly the same as on the road, since the frame is not moving at all under me. Maybe my brain is not working as hard either!

This likely accounts for the fact that in a one hour ride on the road, I can keep my heart rate up at 130-140bpm and suffer no joint or muscle discomfort afterwards, whereas pedalling with what feels like (about) the same force only causes my heart rate to be at around 100 on the trainer.

The inertia of the system is very different from when on the road - instead of a relatively large mass (me + bike) we have just the roller and a small flywheel, and the force on that modest mass is at least as much as the wind drag when on the flat - I think more. Hence it decelerates more quickly between pedal strokes, and there will be more resistance load on the cranks during the "dead" parts of the rotation. This means my legs don't get a momentary rest every pedal cycle as they normally do. This fits with my subjective observation, and experience of riding into a very strong headwind which also hurts my knees unless I take it very easy and/or take a rest frequently.

So I am doing lower intensity riding as warm-up and then intervals. Had a good session yesterday with some walking and jogging up and down the garden in the middle to change the loads on my joints.

PeterH

[531colin]

Road....130/140 bpm with no knee pain
Turbo ..100 bpm with knee pain

If I have got that right, its an obvious mis-match, and I think it must mean that you pedal differently on the turbo compared to the road, which you are used to.
You don't carry round a lot of "spare" muscles so you can't be using "different" muscles, you have to be using all the same muscles, just slightly differently....that is using a slightly different part of their range of contraction, or changing the amount of work one muscle does compared to another.
You are very conscious of a "dead spot" on the turbo, so it might be worth concentrating on "pedalling circles" for a couple of minutes; with cleats, its easy to push and pull the pedals past the top and bottom centres.
You could also try lowering your saddle 5 or 10mm for a few minutes on the turbo....that's not a completely random suggestion, a too-low saddle is much less likely to cause problems than a too-high saddle.

[foxyrider]

Road....130/140 bpm with no knee pain
Turbo ..100 bpm with knee pain

If I have got that right, its an obvious mis-match, and I think it must mean that you pedal differently on the turbo compared to the road, which you are used to.
You don't carry round a lot of "spare" muscles so you can't be using "different" muscles, you have to be using all the same muscles, just slightly differently....that is using a slightly different part of their range of contraction, or changing the amount of work one muscle does compared to another.
You are very conscious of a "dead spot" on the turbo, so it might be worth concentrating on "pedalling circles" for a couple of minutes; with cleats, its easy to push and pull the pedals past the top and bottom centres.
You could also try lowering your saddle 5 or 10mm for a few minutes on the turbo....that's not a completely random suggestion, a too-low saddle is much less likely to cause problems than a too-high saddle.

What Colin says

one question though, 130/140bpm seems fairly high unless you are race training, for example i did my 4 hours plus today avg 125bpm avg speed @ 15mph, if i see too much in your range i'm either going for it or ill!

So are you training for competition, eyeballs out or just doing lighter aerobic endurance rides?

[thatsnotmyname]

one question though, 130/140bpm seems fairly high unless you are race training, for example i did my 4 hours plus today avg 125bpm avg speed @ 15mph, if i see too much in your range i'm either going for it or ill!

HR response is unique to an individual. Comparing two different HR outputs from two different people is meaningless. Even if they were the same age and performing exactly the same exercise you would not necessarily expect them to be the same.

If I have got that right, its an obvious mis-match, and I think it must mean that you pedal differently on the turbo compared to the road, which you are used to.

Everyone pedals differently on a turbo - or at least they 'ride' differently. Fixed trainers generally only employ the legs, while road riding would also employ arms, core, upper body and a host of other muscles, most of which you don't necessarily notice, in order to keep the bike upright and level.

Generally though, as mentioned earlier, the issue is most likely to be excessive roller pressure from the 37mm tyre. Hopefully, the narrower/lower profile tyre will have sorted it..

[peterh11]

Road....130/140 bpm with no knee pain
Turbo ..100 bpm with knee pain

If I have got that right, its an obvious mis-match, and I think it must mean that you pedal differently on the turbo compared to the road, which you are used to.
You don't carry round a lot of "spare" muscles so you can't be using "different" muscles, you have to be using all the same muscles, just slightly differently....that is using a slightly different part of their range of contraction, or changing the amount of work one muscle does compared to another.
You are very conscious of a "dead spot" on the turbo, so it might be worth concentrating on "pedalling circles" for a couple of minutes; with cleats, its easy to push and pull the pedals past the top and bottom centres.
You could also try lowering your saddle 5 or 10mm for a few minutes on the turbo....that's not a completely random suggestion, a too-low saddle is much less likely to cause problems than a too-high saddle.

What Colin says

one question though, 130/140bpm seems fairly high unless you are race training, for example i did my 4 hours plus today avg 125bpm avg speed @ 15mph, if i see too much in your range i'm either going for it or ill!

So are you training for competition, eyeballs out or just doing lighter aerobic endurance rides?

That is a fairly high intensity one hour ride. If going for 4 hours the average will be a fair bit lower, nearer to what you quote. If I am in the gym doing interval (HIIT) I will push it up to 150 or so in the intense phase.

Regarding Colin’s comments, actually what I notice is that there is a load all the time. On the road I normally put most of the power in (like most people) on the downstroke. I take the weight off the pedal on the upstroke but I am not pulling the pedal. So the knee is pretty well unloaded in that case, whereas the deceleration on the trainer causes constant load. I agree that the leg muscles are being used differently, partly because of this effect. However, at least when climbing I think that I usually use some upper body muscles which are not in play on the trainer. Hmm. I shall observe when I get back on the road - hoping I can do that by early next week as we’ll have done our two weeks total isolation after suspected exposure to Cov-19.

PeterH

[CyberKnight]

are you reading the settings right, my turbo is also a dumb magnetic one with difficulty of 1-5 . 5 is the hardest

[ossie]

I had some knee discomfort on the turbo over the winter period and not for the first time.

Its disappeared within reason in the last week or so now out on the road.

Interestingly I jettisoned the saggy brooks for a new saddle from Spa, without doubt I'm sitting higher from the pedals (only slightly) and that may have helped. On tour, on occasion I will get almost instant knee relief with a saddle adjustment .

That said on the turbo I will usually work a lot harder in a shorter period than I do on an average ride.

[peterh11]

Continuing the saga ... thanks everyone for your comments and suggestions.

I got the new tyre - 28mm instead of 37mm- and installed. Yes, it makes a difference, subjectively about 1 gear's worth, hence reducing the uphill effect. I also experimented with how tight I had done up the fixing bolt on the trainer and seem to have been a bit over-zealous in my aim to avoid the bike falling off, so I backed it off a bit till I had the bike still firmly held but the wheel rotating freely with the roller away from the tyre. That makes a little bit more difference and I'm probably not damaging the bearings so much!

Finally I have raised the saddle a few mm which may also be helping my knee, and tried out raising the front of the bike to feel more like a slight uphill ride (not sure if I will continue with that, though I might just vary it from ride to ride). I am still using setting #1 on the adjuster which is the lightest load (I tested).

I did a 20 minute session this morning with all the above adjustments before starting a general core strength and flexibility routine (from "The Pain-Free Cyclist" by Rabin and Hicks - which I rate as a good book for learning more about how to keep yourself from injury on a bike). Seemed good and I was able to drive my heart rate up a bit more - several minutes at 120bpm+

Still not like riding on the road. I did go out for half an hour yesterday around town and it's so different and so much more fun. I definitely use the upper body and arm muscles more when riding for real. Interesting too, to see how the town is so quiet - I stuck to main roads mainly as there was so little traffic and that made it easier to stay away from pedestrians and other cyclists. (Different bike - Luckily I have two similar steel touring bikes so I can leave the new/best one set up for "real" riding and adjust the older/second-best one for the trainer.)

It occurs to me that I don't do a lot of climbing, living in Cambridgeshire. It's not totally flat if you ride south into north Herts as I tend to, but the climbs are short and there is only one hill within 2 hours riding which is above 10% for more than a few yards. So I will persevere with short/interval sessions on the trainer and aim to improve those muscles as I want to go further afield once the whole C19 situation eases.

PeterH