Ok, so I’m a power junky. I bought a power meter for my MTB bike. I’ve done a few XC races on the MTB that were about 2 hours total time. Here are a couple observations. I don’t know if this is me or if it would apply generally. Just random musings… not sure I really have a question. Just thoughts.
I generally put out much more puncheur style power on the MTB than on the road. Lots of big spikes. I’ve seen that question on the forums a bit and had it myself. The Puncheur focus seems very suited for type of event.
I’ve had some efforts (races) on the MTB that left me wasted and questioning my life values at the end. But Xert rated them only moderate. I’ve noticed on the road I tend to put out a more consistent and higher average power for the duration. I suppose Xert doesn’t know the difference between traveling down a smooth road and bouncing around over a rough/rocky trail.
Ad.2) Exactly, XSS captures the load coming from generating power by „turning the pedals”. However, this is not the only load your body is taking. In particular MTB requires a lot of bike handling effort and cognitive stress. Imagine difficult, technical descent on a mountain trail: you could be very exausted at the end of it, even if you didn’t make a single turn of the cranks And XSS or any other power meter based metric will show „0” load/stress.
I think this is exactly part of what is going on. Both my last two races had around 3000 ft of climbing. But It was a loop so I had just as much descending… and yes, the descending was rowdy and fast.
Here is an example of an mtb Ride that was not a lot of elevation gain though. It was fairly flat. It was pretty chunky and I gave a hard effort though. Hard to say if it was really only moderate. I tried to get a Strava KOM. Ended up with 4th lol.
Workout/ride classification depends on the profile math.
Difficulty Rating: Easy, Moderate, Difficult, Tough, Hard
Specificity: Polar, Mixed, Pure
Focus Duration: 2 min (Road Sprinter), 3 (Pursuiter), 4 (Puncheur), 5 (Breakaway Specialist), 6 (Rouleur), 8 (GC Specialist), 10 (Climber), 20+ minutes (Endurance - Sprint TT thru Triathlete)
Difficulty Score is the exponentially weighted moving average of XSSR.
A rough gauge of difficulty can be determined by looking at your XSS versus time.
Example: 134/1.75 hrs = 76 which hits Difficult (76-110), but the weighted average score for the ride was below that.
One easy way to visualize difficulty is how often and how deep MPA is pulled down during the activity.
As mentioned, you also don’t get any credit for handling gnarly descents.
Concerning effort results/descriptions for MTB activites in Xert has created a bit the same thoughts
for me personally.
Giving it a powerful gravel/wood cross-ride on the heavier MTB on flat terrain (no descents) with an
average cadence of 93 rpm and a HR around 150 bpm results in an “Easy” difficulty rating/score.
An average Watt value of 254 was rated for the same ride on another platform, but that should’nt
count to much (or should it?).
Riding on gravel or in the woods, cornering and “breaking away” after slows/stops is certainly quite
different from riding on the road (concerning “XSS MTB vs Road”). Somehow (and that’s the reason
for thinking about it) these MTB actions/efforts are not quite represented in the HR received data.
Maybe (…maybe) a power crank/meter on the MTB might “solve” this “issue”. I think HR isn’t just
quite able to pick up quick actions/efforts like breaking away/power sprints on X/MTB/in common.
Cross efforts which gained real results: Shortly after having done a couple of X/MTB rides on hilly
and steep gravel/rock terrain, it was/felt very easy to break away from friends in a road group ride
after around 70km . That’s for shure a fine effort/result for the road …from past X/MTB activites,
which surprised me personally but also the plain data/graphs didn’t show.
I guess the MTB vs Road subject (if it is a subject?) goes on/has to go on! And if you do ask a BMX
racer, it turns out these riders are the very best break away sprinters no data does know about .
I have a 4iiii single-sided crank on my FS mtb, bought from reading the positive reviews from here , during one of the Covid lockdowns when my trainer broke and none were available to buy. Find it real doing intervals on hills, though you do have to see target power as a range rather than a single figure. Great for endurance rides and keeping power below a certain level. For group rides I don’t look at it!
I’m an amateur MTB racer, and I have been training seriously for more than 10 years, the last 5 years with a trainer with Power Meter and the last year with Power Meter pedals in my MTB and in the Hybrid I use for training. (I don’t do road).
XERT is great to train with the trainer and to check my long rides with the hybrid bike, but is very frustrating to see how low is the load of a MTB ride vs road or trainer. I believe this is due to the spikes in power that although it is tough it results on a much lower normalized power.
On my 2-3 hour races where I ride as hard as I can and here in Florida where there are no downhills we pedal most of the time, I get loads very low if I compare with the effort. I wonder if a bit different algorithm could be use to calculate MTB rides. Maybe using HR… I know is not as reliable than power and it changes with many factors, but if I ride 2 hours at my top Threshold HR, elevating it by 3 that should count a lot and I feel it does not.
So it’s been 2+ years since I posted this. I still have the same general problem. Same power meter on the MTB.
In the winter indoor training on a trainer, my FTP goes way up (feels accurate though). Then as I transition to summer MTB races I don’t get much credit for XSS. Yesterday got 99 XSS and my buddy w/ a heart rate monitor but no power on same ride got 360. (We have similar FTP).
So, I think we hashed this out the reasons why. New question, what are the alternatives for fixing it? Mark my MTB rides to use HR instead?
The net effect of this is that during the summer months, Xert is always suggesting more XSS than I can handle and saying I’m behind where my target is. So to compensate I’ve usually just set my ramp rate to “off season”. and bag it until winter starts again. Seems to defeat the purpose though and I’m questioning whether or not to just subscribe 3-4 months instead of yearly.
To fix it … (I’m the same by the way in that I ride MTB, with occasional road, and tend to use the trainer more in winter), I eventually took the plunge and largely did things myself.
There isnt a platform that can do this all for us. If we were all billionaires I guess we could employ expert coaches to help us day to day.
So in the end (having historically used plans on lots of platforms (most recently here), I realised that there’s no substitute for knowing our own ‘state’ and no bit of software can really help that. More so when we don’t fit the ‘model’.
So yeah, use platforms for workouts for some ‘engagement’. Good for metrics when you do do a ride that gives you some sense of ‘where you are’.
How much riding to do though … pick a method and diy was my conclusion.
Same PM refers to using the same item or just the same model? But then there is at least also the trainer as another PM, no?
In any case, if I’d use more than one item I’d cross test the powermeters (pedals versus trainer) using something like https://compare-the-watts.com/
I wouldn’t give much on that HR derived load of you friend. Might be his signature is too low or provided HR value ar not correct or whatever.
Before anuthing, cross compare your PMs (MTB versus trainer).
I like the idea of applying some type of HR check to MTB rides that affects the tabulated strain score for low/high/peak.
There is likely some characteristic of MTB rides that would allow those activities to be analyzed differently. Or at least those portions of MTB rides that involve lots of technical maneuvers including descents.
For example, an obvious rise in HR when cadence is near zero compared to coasting on the road which would normally mean the opposite.
Or high strain intermittent power bumps indicating a tough technical section where the power is inconsistent but HR is steadily rising.
IOW some recognizable pattern that would allow XO server to identify offroad activities and apply a scaling factor to the strain score.
I think the main issue is simply that there is more coasting on an MTB, even though the rest of your body might be working while you are coasting. The MTB workout might feel as hard as a road ride, but the cycling part (i.e. the work done by your legs) is less. It seems reasonable to me that cycling-specific XSS is lower as a result.
Having said that, I do find that XSS gives me much more appropriate “credit” for MTB workouts than the alternative measurement used by TrainingPeaks and others - TSS.
The author of the topic is right! I did not have a power meter on the MTB bike, but as it turned out, XERT only wants to see power and the load is not calculated by heart rate. Then I bought a power meter and indeed, after several races, I was upset that in fact I was half-dead and XERT tells me that I was only slightly loaded. (Let me explain, I have a road bike with a power meter and there is no such problem.) This is clearly not perfect in the load accounting model and it will eventually be annoying, since the xert will give you an excessive load. Perhaps there should be other tools/options to improve this?
That could be a simple workaround if the feature were added. Long term I think there’s a way to analyze the activity during upload, determine the data includes sections of low/no power or cadence but HR tells a different story, and apply a scaling factor. This would handle MTB, CX or any ride where you’re aren’t pedaling but the strain score should be higher. For example, a road/gravel ride might include X minutes of pushing your bike uphill or carrying it. That period shouldn’t rate as easy when HR-wise you may be in tempo or threshold territory (moderate or difficult XSSR).
An easy way to test this is to export the FIT file, use FitFileTools.com to change the date/time stamp and strip the power, then import the result into Xert and compare the ratings to the original activity.
For example, if the actual ride ended at 2pm set the time stamp on the FIT file to 2:10 pm so it won’t be treated as a duplicate when imported.
Compare the two entries and if you agree with the difficulty and strain score, delete the original activity.
I’d be curious what the average % difference is in XSS for a sample data set of say 5 rides of various durations.
I experience the same problems with MTB rides and do use only heartrate to evaluate the workout in Xert. It is closer to the truth, but also does not give you the full picture as short punchy efforts with high wattage are not visible due to slower reaction of the heartrate.
All the athletes training with power I know do wear a heartrate belt in addition, so the data should be available anyhow. Therefore a training tool should ideally take both measurements into account, because Power measures how hard you are working, but the heartrate measures your body’s response to the workout.
Maybe HR should be considered as part of any activity. I know the reasoning behind just looking at power but if I’m riding along with a lower power and my HR is abnormally high compared to other activities, is that not telling me something?
I agree! It can highlight the extra strain of off-road riding, but also things like heat, fatigue, illness etc can be reflected in HR vs power discrepancies and would be useful to account for in the model.
And XSS or any other power meter based metric will show „0” load/stress.
. That’s for shure a fine effort/result for the road …from past X/MTB activites,
.