Efficiency - Road versus MTB

[dusty_nz]

Have just completed a large Enduro (almost 1000km in 9 days) and working out the stats noted that the Calories consumed via Garmin and strava are for a road bike.

Eg both use the principle of assuming* constant road friction, wind resistance etc for a generic road bike. This allows you to calculate the calories consumed of moving a mass (Rider + bike) over or up a distance.

Have had a google and can't find any approximations for this on a MTB. Eg greater rolling resistance, Greater wind resistance and surface varies greatly between logs, sand, rocks etc.

Some of the rides I have done Strava indicates around 6000 calories consumed. Would a MTB on generic surface be 20% or more higher than this assumed* figure?

Thanks

 

[Mywifesirrational]

There was a study done back in the 90's that compared energy expenditure MTB vs roadbike with the road bike over a given distance being 30% more efficient. It was done with 26 inch wheels on the MTB (no idea if 29 make a difference? I presume it would), on the same paved surface, no idea how 'knobby' the tires were.

It's a little bit hazy now, but over a given distance the MTB used more energy as it was slower, so the rider took longer to complete the distance - hence one of the less obvious contributing factors to a higher energy expenditure. Another element was the difference in rolling resistance, the road bike was obviously better (the comparison was done with on the road for both). In an off road sense, logic suggests to me that energy expenditure would have to be higher from the elements you have highlighted.

Another thing to consider, if your not taking HR into account for energy expenditure, it's unlikely to be accurate - HR has a very predictable and linear relationship to energy output, are you a payed up member of strava - does it take HR into account for calculating energy expenditure?

I'll see if I can track down that study. 6000 calories doesn;t seem excessive to me for massive rides - how many hours in the saddle (5+ hours?)? How much speggetti each night :hungry:

edit Just had a look, plenty of studies into MTB energy, multiday races, road... I'll have a look tomorrow at work, can't access them from home, without going through the god awful remote access crap.

 

[dusty_nz]

Agree with Heart rate however its a very personal thing number as what I generate at 150bpm is totally different from another person.

As such Strava and garmin can't use it.

I have a nice long hill down the road from mine. Was going to ride it at a constant HR on the road bike then do the same on the MTB at the same HR. The different on speed would identify the difference.

The biggest day for the ride was 138km and 2115 meters climbing. this was a ride time of 9 hours in the saddle at an average of 161 watts.

Strava gave it 5800 calories which seems light.

 

[pharmaboy]

Have just completed a large Enduro (almost 1000km in 9 days) and working out the stats noted that the Calories consumed via Garmin and strava are for a road bike.

Eg both use the principle of assuming* constant road friction, wind resistance etc for a generic road bike. This allows you to calculate the calories consumed of moving a mass (Rider + bike) over or up a distance.

Have had a google and can't find any approximations for this on a MTB. Eg greater rolling resistance, Greater wind resistance and surface varies greatly between logs, sand, rocks etc.

Some of the rides I have done Strava indicates around 6000 calories consumed. Would a MTB on generic surface be 20% or more higher than this assumed* figure?

Thanks

Garmin doesn't differentiate between road and mountain.

Strava does. When you setup your bikes, you select mountain or road and strava uses an algorithm to calculate power used , however they assume the Mtb kms are offroad , so mountain biking on a road would overstate your calories used, but offroad might be pretty close.

Dusty_nz, you need to do 2 tests, one riding up a nice long hill, preferably one that will keep your road bike speed below around 25kmph. This will give you the rolling resistance difference between the 2 bikes.

THEN, you need to do a flat Time trial also at a constant output on each bike. This will give you the difference between the bikes taking both rolling resistance and wind resistance into account. Because WR goes up by a square and RR is linear, the differences will not be constant in the 2 experiments.

Going up a hill, I suspect the difference will be 25% but on the flat probably only 15% or less at 40kmh for the road bike ?

Be an interesting experiment- just use strava, make the tests short and you can probably do them on one day especially if you keep yourself at threshold or below.

 

[driftking]

MWI
that's interesting about heart rate. I understand it has a linear association with calories but doesn't this only go as far as the individual? I mean two people who mimics the same heart rates will rarely ever burn the same calories even if all other factors or the same. Given the obvious one of BMR as the first issue but the efficiency of the athlete will be huge.

Iv never trusted calorie counters on monitors, they miss too much crucial information. At the best they give you a reference point you can call point X
You just need to hit your target each time. Whether its accurate or not the point of referance is the Important factor.

 

[Mywifesirrational]

MWI
that's interesting about heart rate. I understand it has a linear association with calories but doesn't this only go as far as the individual? I mean two people who mimics the same heart rates will rarely ever burn the same calories even if all other factors or the same. Given the obvious one of BMR as the first issue but the efficiency of the athlete will be huge.

Yeah, that's an interesting point, efficiency is basically the level of skill at a given task, better the skill, greater the efficiency - But to compare Ian Thorpe against my doggy paddle, at the same HR we are both expending a similar amount of energy, but since he is infinitely a better swimmer than me, I've traveled half a lap, he's done 4+ in the same given total energy expenditure - presuming this is a sub maximal effort. In a maximal effort he undoubtedly can expend a greater deal more energy than I can at my maximal, not because of skill, but since he's is a great deal fitter has more metabolic 'machinery' to drive this at maximal effort. But also if we both swam 1 km at a submaximal effort, I would have used a great deal more energy as I have spent a great deal more time to complete that 1km. this is perhaps underlying the principle of cross training in weight loss, as you get more efficient at a task, you use less energy to complete it, unless you push yourself harder and harder (the average punter does not like this requirement).

Perhaps a better thing I should have said was that energy expenditure is relatively predictable to HR within a given individual and we can express or compare that against other people not in absolute terms, but in a percentage change is they progressively go harder - so from resting HR/energy expenditure to maximal HR/energy expenditure the change would be relatively similar amongst all individuals.

Not sure if that was a rambling mess or makes sense? long day in a sunless lab.

 

[LJG]

I've always ridden some sort of mtb or flat bar bike and so has my son, we've also always ridden in the bush. He recently went to Scotland and met his fiance's parents. The father and brother are mad competetive roadrace riders (both skinny and obviously untrustworthy haha).

They took him on a ride (even made him wear lycra's :faint and he said to me you have no idea how easy and how fast a high quality roadrace bike is. He said you just don't seem to use anywhere near as much energy as a ride in the bush. He could not give exact figures, but just based on general "feel" he reckoned a 50klm bush ride with the usual up and downs etc would roughly equal between 150-200klm on a road ride with smooth flat tarred road. They did a 20 mile ride (32klm) and they rode as fast as the other 2 could go and he was breathing normally and had not even raised a sweat when they finished. He reckoned he would expend more energy in roughly 10 minutes in the bush here. Mind you, he is super fit, I mean really fit!


I know there is nothing scientific about his observation but I thought it was interesting to get "seat of the pants" thoughts. The best bit is her parents are coming over here soon - so I'm trying to talk my son into getting a lend mtb bike so we can show him good Aussie bush riding and run him around till he drops hahahaha

 

[dusty_nz]

I've always ridden some sort of mtb or flat bar bike and so has my son, we've also always ridden in the bush. He recently went to Scotland and met his fiance's parents. The father and brother are mad competetive roadrace riders (both skinny and obviously untrustworthy haha).

They took him on a ride (even made him wear lycra's :faint and he said to me you have no idea how easy and how fast a high quality roadrace bike is. He said you just don't seem to use anywhere near as much energy as a ride in the bush. He could not give exact figures, but just based on general "feel" he reckoned a 50klm bush ride with the usual up and downs etc would roughly equal between 150-200klm on a road ride with smooth flat tarred road. They did a 20 mile ride (32klm) and they rode as fast as the other 2 could go and he was breathing normally and had not even raised a sweat when they finished. He reckoned he would expend more energy in roughly 10 minutes in the bush here. Mind you, he is super fit, I mean really fit!


I know there is nothing scientific about his observation but I thought it was interesting to get "seat of the pants" thoughts. The best bit is her parents are coming over here soon - so I'm trying to talk my son into getting a lend mtb bike so we can show him good Aussie bush riding and run him around till he drops hahahaha

There certainly is no question on how much harder the MTBing is compared to road (Per Kilometer). The burst power and also the demands on the upper body as well.

I suspect that per time they are similar. Eg 1 hour MTB will use the same energy as 1 hour of road road assuming similar levels of enthusiasm.

There is also physical strength, Most roadies going MTB simply die due to undeveloped upper body. Same logic as a top rider does not make a good runner.

 

[carpetrunner]

kJ/min from a good HRM is the key

Assuming you are in the same condition before you start either a MTB or road session - the easiest thing to measure to compare MTB/road is your Calorie burn rate (kJ/min) with a good HRM.

Garmin (standard) and Strava don't use HR to calculate calories burned - they work backwards from the work, calculated from speed elevation and bike weight. So the sample rate and elevation accuracy of your GPS track has a huge influence. If you use the Strava basemap for elevation vs raw GPS data vs garmin hybrid gps/barometric you will get wildly different answers for calories burned >20% When you combine this with your average dirt session where most efforts are 1 to 5m climbs and tracks that can take a full U turn within the accuracy of your GPS then Strava is really only taking a guess.

I used a Suuto HRM that calculated Calories burned from HR for a few years. Suuto use an algorithm that calculates different calorie burn rate for different HR (you can set up your Garmin to do this with a new leaf profile.) kJ/min is a pretty good reflection of the effort in a session, compared to say average HR. Now on the road I use a powertap so I have even more data to back up what I think is happening. For the MTB without the powertap, I have enough data to estimate TSS from my HR data.

Back to the original OP's question... "it depends". Most MTB is a series of short(5s) high intensity intervals - which strava/garmen is only guessing at, most road rides are relatively long constant efforts - which Strava/garmin is good at. For the same time and the same average HR you will feel a heap more shagged doing the intervals, but strava/garmin may not know it.

Of course you could ride road crits and be doing similar high intensity intervals, or you could ride long open firetrails and be closer to the road-ish long constant efforts.

- carpetrunner