Sunday, July 29, 2018

Trainer vs road cycling, psychological and physiologic comparisons

We know all too well the hesitation to use indoor sports equipment such as treadmills and exercise bikes.  Let's face it, they just are not pleasant to use.  I'll take a ride in the rain any day rather than get on a good turbo trainer.  However, putting preference aside, do they provide the same degree of physiologic challenges to the cardiac, respiratory and local muscular systems?  While using my own bike on the turbo trainer, I noted the perceived effort was way higher than my physiologic metrics indicated.  However, the metrics were similar to the road riding data.  I decided to look into this further and report on some literature as well as my personal measurements that help reconcile this.

First off, is my perception of a higher relative effort valid?  
A study was done comparing an outdoor 40 km time trial with an equivalent indoor simulated time trial (subjects personal bike on a computrainer).  The instructions were:
Therefore, same bike, same perceived effort but no feedback such as power, heart rate were allowed.
Results were quite interesting:

The outdoor trial was associated with a much higher average power (205 watts) than the indoor trainer (163 watts).  With the higher power came a higher average heart rate in the outdoor trial (152 vs 143).  The RPE and core body temp were statistically the same.  Therefore, despite the same bike/riding position, an indoor ride will have a drastic reduction in power at the same perceived effort.  Conversely, an outdoor ride, at the same perceived intensity, will yield greater physiologic stress and presumed benefits from the work out.  Other studies have not shown dramatic difference in physiologic metrics, but were done differently.  Either instructions were given to do a max effort, or heart rate/power was available for the subject to see.  
For example:
 The above study was done at maximum time trial effort:
"After a short rest the subject was asked to
cover a distance of 40km in the shortest time possible achiev-
ing the highest average power output. Feedback in the form of
heart rate response (b ´ min±1), elapsed time (min: sec), and
percentage distance covered were the only visual cues given
during the trials"

Bottom line:
At equivalent power and heart rate, the relative perceived effort will be higher on an indoor trainerTo reach the same physiologic targets, a much higher discomfort level must be endured.  No wonder most people don't like riding indoors!

It appears that the physical benefits can be equivalent on a trainer but only with sufficient effort.

However, what about issues such as muscle specificity and overall cycling efficiency while riding a turbo trainer?
This study looked at exactly that using EMG as well breath by breath analysis for calculations of efficiency.  The test condition was cycling on a treadmill vs using an electronically controlled turbo trainer.
From the paper:
"Pedalling technique was quantified by a novel parameter that
described the distribution of power during the pedal revolution.
The minimum power outputs during the pedal revolution (i. e.,
the dead centres) were expressed relative to the overall power
output and described as ‘dead centre size’ (DC) [ 21 ] . Leirdal and
Ettema [ 22 ] showed a positive correlation between efficiency
and DC and thus pedaling technique."

The EMG data did show some differences:
The RF was the main muscle of difference and theoretically could be an issue especially for Powercrank users (such as I), since studies have shown that the RF is more heavily utilized with that pedaling modification. What the significance of these differences would be in practical terms is not clear.
Here is a further look at mean muscle EMG activity as power is increased.  There is again differences in the RF and BF (hamstrings):

Dead center data:
And finally their conclusion:
Their bottom line:
Turbo trainer EMG and pedaling technique are subtly different than road cycling but do not appear to impact efficiency.
One condition they did not test for was the effect of a road ride up a slight incline.  The trainer ride does feels more like a mild steady incline than a flat road (the flywheel helps of course but is not the same as a road feel).  Perhaps that condition would have yielded different EMG patterns closer to the trainer?  Arguing against this simple explanation are studies showing that pedaling mechanics and muscle EMG patterns are not altered with uphill riding.   This is a figure from the above paper showing that seated uphill and level cycling have very similar muscular patterns (as opposed to standing):
On close inspection, there are tiny subtle changes of unclear statistical and physiologic significance between incline and level seated riding.

On to my data.
My original purpose in getting a trainer was to recreate the interval efforts I have been doing and then determine finger-stick lactate values over this time.  Outside blood measurements in the heat/humidity of Florida are just not possible with the Lactate Scout (error 1 always seen).
As I was using the trainer, I was struck by how hard I was seemingly pedaling but the "numbers" were not showing costal O2 drop, heart rate elevation as they should.  This now makes sense in view of the first discussion above.
Lets now look at my physiologic metric comparison, specifically Hexoskin cardiac, respiratory data, costal and leg muscle RF SmO2 vs power.

The following interval tracings pairs were done in the same session, first a road ride of about 2 hours (1 hr warm up, interval, 1 hour back), then immediately putting the bike on the turbo trainer.  Another 10 minute or so warm up is done then the same interval was repeated.

Even start on the road at 330 watts:

Measurements include 
Costal O2 dropping from 58 to 23%
L RF SmO2 dropping from 47 to 8%
Heart rate max 168
Minute ventilation at 30 seconds - 105 L/min
Minute ventilation at end 210 L/min, with transient rise to 226 afterward
Respiratory rate at 30 seconds - 46/min
Respiratory rate at end 59/min

Even start on the trainer:

Measurements include 
Costal O2 dropping from 56 to 13%
L RF SmO2 dropping from 46 to 6%
Heart rate max 167
Minute ventilation at 30 seconds - 118 L/min
Minute ventilation at end 214 L/min, with transient rise to 233 afterward
Respiratory rate at 30 seconds - 39/min
Respiratory rate at end 55/min

  • Allowing for some random fluctuation and noise, remarkably close.
  • There is some additional O2 drop on the costal area, but the hypoxic shaped curve is very similar.  
  • The RF data was pretty close as well, but since O2 extraction was near complete in both cases it is difficult to judge in my opinion.  
  • Certainly, heart rate (single lead EKG) and respiratory rate/volume were close

Next case, Fast start at 310 watts:

Fast start Road interval with bilateral costal O2:

Same graph interval but looking at R RF muscle O2:
Measurements include 
R Costal O2 dropping from 73 to 36%
R RF SmO2 dropping from 75 to 54 rising to 61%
Heart rate max 163 early in the interval
Minute ventilation at 30 seconds - 100 L/min
Minute ventilation at end 209 L/min, with transient rise to 219 afterward
Respiratory rate at 30 seconds - 40/min
Respiratory rate at end 56/min

Now for the trainer data
Bilateral costal O2 and power:


R RF muscle O2:

Measurements include 
R Costal O2 dropping from 72 to 36%
R RF SmO2 dropping from 69 to 55 rising to 58%
Heart rate max 162 later in the interval
Minute ventilation at 30 seconds - 100 L/min
Minute ventilation at end 208 L/min, with transient rise to 219 afterward
Respiratory rate at 30 seconds - 44/min
Respiratory rate at end 50/min

  • The R RF deoxygenation curves are very similar.
  • The costal deoxygenation curves are also extremely close to each other.
  • Both respiratory rate and minute ventilation are on par with each other, although rate seemed a bit less on the trainer toward the end.
  • Heart rate curves are slightly different but max values about the same. The heart rate rapid rise is present in both cases but there is a slow rise on the indoor trainer as opposed to a slight decrease riding on the road.
One of my continuing interests is in the Fast start pacing strategy of Dr Stephen Bailey.  A difference in technique (amount and duration of fast start) may not be the only variable when comparing my observations to that published.  They use a trainer indoors (understandably considering what they are measuring):
Would the results be different on an outside road condition?  Probably not, but I need to keep testing conditions in mind as further trials are done.  One of the major differences that I am seeing with the Fast vs Even start pacing is that of heart rate trajectory.  At least on this limited look at indoor trainer vs outdoor comparisons that differential may become blunted.

Road/Outdoor vs Trainer/Indoor cycling generalizations:

  • Perceived effort is higher on an indoor trainer.  Whatever the reasons (distraction riding outside reducing RPE), it is something to consider in attempting to simulate an outside road ride.  It also helps to explain why many of us consider indoor riding so unpalatable.
  • Overall cardio-pulmonary impact at equivalent power outputs is very similar in both conditions.  Heart rate, respiratory rate and minute ventilation were all similar between test conditions.  However they may be some subtle differences in heart rate patterns in the fast start road vs trainer.  This may also translate to lower costal and RF SmO2 at interval end.  I need to explore this further.
  • There were subtle alterations in pedaling mechanics and muscle usage with a turbo trainer.  Whether this is going to impact road riding specificity is not clear.  It is also possible that these changes resemble outside riding up an incline however literature does not support the EMG changes that are seen with this.  The RF is the muscle group that seems to most affected by trainer use.  However, NIRS measurements of this muscle did not show marked difference while using a trainer.
  • Lastly, the Hexoskin, BSX sensor combo is a helpful tool for home physiologic testing and metrics.

This post is dedicated to my son Kipp who uses a trainer exclusively (performing multiple intense intervals) and has become a gifted cyclist as a result. 

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