Counting Calories with Kiddie Bike Trailer

Hello Everyone!

I have been having a heckuva time trying to extrapolate the calories I am burning by riding with a bike trailer, towing my son and his gear.

I am approx 5'10" 240 strong build but can stand to use a few pounds...

Riding an MTB
pulling a double seat Chariot Trailer (2 wheels, estimated total weight including kiddie is about 65lbs)...

Lets assume a 1 hour ride at 15MPH which I can maintain with an average HR of about 164...I can ride in the low 160's for at least 1 hour if not more. Longer rides I tend to average in the mid-150s or lower when we dial the pace back to 12.5-13.5MPH...I don't like to ride slower than that because my HR never gets over 135...

 

Get a heart rate monitor! I have a polar that cost about $70.00 and it also calculates calories burned taking weight, height etc. into account.

 

I do but sometimes it cooks up numbers I don't trust. Like on a 2 hr ride it will calc out to 3800 calories or so. It's a SigmaSport PC14. I suppose it could be right...but that is a lot of calories to burn on a 2 hour ride going 15MPH even with the trailer unless I am missing something.

 

3800 does sound high, but if your heart rate average is over 160, it is possible, I suppose. Let me contact a fanatic friend of mine and ask what he thinks. He is a machine. I'll post his response.

 

I have poked around on the web looking at cycling calorie calculators and some of them do come real close to the 3800 figure for a hard 2 hour ride, if I add the weight of the trailer and child into the calcs. But that is not entirely fair because the weight is not part of my body and therefore not a part of the metabolic section of the calculations. it is however part of the mechanical section of the calcs. Add to that another layer of complexity is the additional rolling resistance of the the two wheels and the aerodynamic drag created by what amounts to a rear scoop attached to the bike. There is even a marked difference between the load created when I use the eisenglass cover over him in cooler weather, versus just the bug screen which allows air to scoop into the trailer.

Lets look at this another way.

I can ride the same 14 mile out-and-back on our Northern Central Rail Trail in approximately 45-47 minutes whereas the best I can puke out with my son is about 56 minutes. Both scenarios are high levels of effort I would say 80-90% effort. I actually use my HRM to make sure i don't go over 180...I generally start to back off if I see the HR digging into the mid-170's. I am not at the point where I am working anaerobics yet in my return to serious riding. I am still building a cardio-base and essentially my son (Brandon) is my secret weapon. He definitely adds significant load to the ride, and he likes to go fast...haha. My riding friends don't like to ride with me when he's not attached because they wind up getting dropped or are huffing to stay even in the draft. Some of my friends need to get in shape...I am probably still back of the pack in a Cat 5 Road Race, just transferring what I know from racing Clydesdale Cross-Country MTB.

I just think there must be an angle of this that can be looked at to arrive at some reasonable conclusions. I thought about just using the time/distance without him vs with him, but I don't even think that is fair, because generally I am much more fatigued at the end of the ride with him. My legs are generally more sore, and i know there is more lactic acid buildup.

 

Sounds like those calculators need some repair.

3,800 Cal at a metabolic efficiency of 25% mean actual work performed at crank/rear wheel is approx 3,800 kJ.

3,800 kJ over 2 hrs is 1,900 kJ/hr

1,900 kJ over 3,600 seconds = 528 watts average power for 2 hrs!

I don't think so

 

well that's exactly it....I am probably in a minority of folks that actually train harder with thier kids in tow, but I look at it as an opportunity to burn more of those calories and it definitely makes me stronger. My acceleration when he's not back there is improving significantly, although he does hurt my higher rpm sprint work. i find myself just grinding the 46/11 gear ratio rather than spinning at higher speeds when riding solo (20MPH or better on the trail)...

The bottom line is I think this particular question has a few angles that I haven't been able to figure out with commonly available tools.

 

Let's assume your threshold power is the same whether or not your kid is attached - a reasonable assumption.

Go out and do a little time trial at your threshold power (that would correspond to the steady-state speed you can maintain for the entire ride). Then go to Analytic Cycling and plug in your numbers to estimate your power. You can then back out the rate of calorie expenditure.

Now go and ride at the same level of exertion with your kid attached. Your power output will be the same, and so will your rate of calorie expenditure. You'll just be going more slowly.

If you can work with perceived levels of exertion, you can do this for work rates below the threshold as well.

 

Yep, 1900 kcal/hr is insane.

Without calculating the rolling resistance, aero drag, etc., etc., I'd estimate between 800-1100 kcal/hr. Not because that's scientific, but rather because that's what normal people are capable of doing while riding between 'moderately hard' to 'hard'.

 

skammer said he weighs 240lbs, so I'm going to guess the high end of frenchyge's range: 1000-1100 kcal/hr going really hard. That's about 250-275w average power: high, but with 240 lbs backing you up I think it's a pretty reasonable guess. Anyway, it's a lot closer to right than 1900! (and the exact value probably isn't very important)

 

This is the response from my exercise guru. See if it rings true for you.

"well it depends on what kind of heart monitor he is wearing. I've had my strap come loose some and claiming heart rates as high as 200+. So if he was moving around alot and not paying attention and his strap became lodged somehow it would greatly affect his results. It would change his average BPM which would change everything. His calories burnt ect.

My next question would be does he have all his accurate information loaded into the system. A change in resting heart rate # or 5-6lbs makes a difference for sure. If his resting heart rate info or something is off that can change things up.

More than likely either he isint using a proper heart rate monitor in which case please direct him to the polar F11 unit. If he is using a polar unit(F6 or higher) then its prolly a problem with his strap like I was saying above.

Make sure the sweet spot and the rest of the front band are fully wet before putting it on and make sure it has a good bite against his skin the in proper place( band should be 1inch below his nipple).

The 3rd and last possiblity is his heart rate runs very high cause his entire system is unhealthy. Higher the heart rate the more calories you burn(its what i've been telling people from the get go) so if he is running a higher heart rate normally then yeah he just burns more calories especially if he is musclar and has good size to him.

I know if I keep a average heart rate of 160 for 2hrs my polar unit will read just like his from above. 3500-3600 cals. I know because i've done it before but, for me to keep my heart up there like that and average that high im working my ass off. So if he was working his ass off for 2 straight hours then yeah its possible the #'s are indeed correct.

Some numbers for refference

6'1 198-200lbs LBM 180 range 25 years old resting heart rate 45 *All figures during a 1hr workout* 120BPM average-850ish cals 130BPM average-920ish cals 140BPM average-980ish cals 155BPM average-1150ish cals

160+BPM average-1200+cals

and i've had some nights averaging 1300cals an hour burnt. My figures have greatly changed over the course of the past year it used to be alot more than that but, im just a smaller guy now and don't carry the same amount of weight around...so I burn less energy."

Don't know if this helps, but this guy is amazing.

 

I've been using HRMs for years, I doubt there is an accuracy or fitment problem. I trust the data being fed into the HRM. I have no reason to suspect a malfunction or otherwise.


What is more likely is the overall fitness level and the level of exertion are the determinate factors.

I would rate my fitness level as acceptable right now...Not great, but improving...I took a few years off riding while starting a family and building a business. Hence the extra 20lbs that need to go...then we'll talk about upping the ante.

I do however exert myself hard 2x a week. I try to ride at least 4x a week...right now I try to go short-hard, long-easy, short-hard, long-easy...any other days are bonus days and I take what I can get. I have been trying to log at least 80 miles a week as the summer wanes into fall. I was clocking 100+ miles with my son at the peak daylight levels. As daylight shortens I trade distance for speed and intensity level. This is on a crushed gravel rail trail by the way...Out-and-back is the way of it. roughly 2% (mild uphill on the way out) and slight downhill on the way back. It's the Northern Central Railroad trail, and a fabulous place to do tempo rides because it's reasonably straight and any changes in grade are gradual. For anyone near the Cockeysville MD area, they know the trail and how great a tool it is for amateur fitness geeks.

To add some feedback on the heart rate thing I have this to say below.
Even back in the day when I was running 2:08 half miles and 4:40 miles, my resting was never below 60...My HR has always run on the high side even when my level of overall fitness was extremely high (4% body fat at one time...BOY WOULD I PAY FOR THAT AGAIN!!!). right now my resting is in the 70's and 80's...it runs higher if I take allergy meds for seasonals...no big surprise there.

 

Good tips above.

That may be what the unit reads, but I don't see any numbers below which would support that for a 2 hour ride.

 

I agree with frenchyge. It sounds like the HRM's are overestimating. If you want an accurate estimate of your calorie usage during a hard workout you have two options: (1) borrow a power meter and do your ride, or (2) do a time trial on a long steep hill (say, >= 6%) with known height. In the case of (2) you can fairly accurately estimate your power output based on your time and your weight, then convert that to calories used.