On April 15th, Isaac Blackman ran the Boston Marathon for the first time.  His previous best marathon was the one he trained for on his own in 2017 to qualify the 2019 Boston Marathon.  What made this race extra exciting for me as a coach (as if having an athlete race the Boston Marathon isn’t exciting enough) was the fact that he bought and started using a Stryd power meter just a few weeks before the race.  While we didn’t change the approach of training for the marathon leading up to the race, I felt I had gained enough insight and data from Isaac using the Stryd device to help him pace his marathon better, and hopefully get a PR in the race.

In 2017, when Isaac ran his Boston Qualifier, he started falling apart after about 21 miles holding a 6:30/mile up to that point.  He was very nervous about running anything faster than that at Boston since he didn’t want to bonk.  I reviewed his training leading up to the marathon in 2017 and noticed he was only running, which greatly effected his Performance Management Chart on TrainingPeaks.  His CTL was in the upper 30s.  Since he was training all three disciplines for the Boston Marathon, his CTL was near 80.  I was confident that he could likely run and hold just a bit faster than a 6:30/mile for the Boston Marathon.  I had arrived to that conclusion around the time he got to Stryd device.  In his marathon pacing/race simulations, he kept on landing right around 290w for his pacing race simulations.  I decided to have him try to hold about 290w for the Boston Marathon and not worry about his pace.  Isaac was not sure how fast to run the opening 3 miles since they were down hill and not sure how hard to push the uphills located from about mile 19 to 21.  The wonderful thing about the Stryd power meter is that you can dial in effort in terms of wattage and not worry if you are going uphill or downhill.  In other words, it makes pacing easier and there is less guess work.  So there we have it – Isaac’s race plan was to hold about 290w for what I thought would be about 2:50 marathon time.

Before we get into the race analysis, I need to define a few terms before we go any further.

Watts – total power produced

Horizontal power ratio – percentage of power producing forward motion.  The higher the ratio, the better

Vertical oscillation – the amount of distance traveled at the center of mass in the up and down motion. Measured in centimeters. Typically less vertical oscillation is better

Stride length – the distance between steps in meters.

Vertical ratio = vertical oscillation (in meters)/stride length (in meters). Lower number is better

Running effectiveness = ((meters/sec)/(w/kg)).  This is often best to look at when adjusted for Normalized Gradient Pace (the physiological cost in terms of pace for running over terrain with elevation changes).  Higher number is better

Leg Spring Stiffness (LSS) – think of this like a spring.  It is energy that is rebounded back into your forward motion after impact.  This is best looked at in relationship to the athlete’s weight in terms of LSS/Kg.  Higher number is better

Ground Contact Time – the time spent per step where the runner’s foot is touching the ground.  Measured in milliseconds.  Lower number is better

This is Isaac’s power file from the race in WKO4 along with his splits below per mile and the power he produced.

PACE (min/mile)                                Power (watts)                             Horizontal Power ratio                        Running Effectiveness (adjusted for NGP)

Mile 1:             6:43                                     274                                             73.9%                                                                  0.92

Mile 2:             6:28                                     292                                             75.1%                                                                  0.96

Mile 3:             6:24                                     294                                            75.1%                                                                   0.95

Mile 4:             6:24                                     289                                             75%                                                                    0.95

Mile 5:            6:23                                      305                                             76.3%                                                                1.00

Mile 6:            6:20                                      306                                              76%                                                                    0.96

Mile 7:            6:20                                      303                                              76.2%                                                                 0.98

Mile 8:            6:24                                      310                                              76.4%                                                                 1.00

Mile 9:           6:23                                       297                                              75.4%                                                                0.96

Mile 10:          6:24                                      312                                              76.8%                                                                  0.99

Mile 11:            6:24                                    302                                              76.4%                                                                 0.98

Mile 12:           6:19                                     297                                              75.5%                                                                0.97

Mile 13:            6:21                                    301                                               76.1%                                                              0.97

Mile 14:            6:21                                    304                                               76.5%                                                             1.00

Mile 15:             6:22                                   305                                               76.4%                                                             0.99

Mile 16:             6:18                                   289                                               74.9%                                                              0.94

Mile 17:             6:29                                    311                                               77.1%                                                             0.99

Mile 18:              6:45                                   302                                              76.1%                                                               0.98

Mile 19:              6:30                                    292                                            75.5%                                                             0.96

Mile 20:              6:39                                    300                                             76.2%                                                             0.98

Mile 21:              6:52                                    300                                             76.7%                                                             0.98

Mile 22:              6:21                                    290                                             75.1%                                                              0.97

Mile 23:               6:33                                   290                                              75.2%                                                           0.95

Mile 24:                  6:34                                288                                              74.9%                                                           0.97

Mile 25:                 6:57                                 273                                              74%                                                            0.96

Mile 26:                 7:30                                 265                                              73.6%                                                          0.95

Final 0.2 miles:      7:10                                 266                                              73.6%                                                          0.93


According to Isaac, the first 3 miles were pretty packed with runners so it was hard for him to get into a rhythm.  This is pretty obvious when looking at the pace and power, especially in the first mile of his run.

In the past, I would mostly look at pace and Normalized Gradient Pace to analyze the run.  If I were to look at just the paces from miles 2 – 23, I would be sitting here scratching my head wondering why Isaac slowed down in the last 2.2 miles of the race so much.  But with the help of the Stryd power meter, I can now see exactly what happened.

As you can see, Isaac ran 10-20 watts on average over his target power for the marathon from miles 5 – 21.  This is a little over 2 hours worth of running.  Running at any speed for any length of time will create some amount of TSS (Training Stress Score), or fatigue.  10-20 watts doesn’t sound like a lot.  But when TSS is calculated, as you get closer to threshold wattage (or surpass it) the relationship to TSS is exponential, not linear.  So 10-20 watts over the course of 2 hours would create a lot more TSS than the target of 290w.  I believe this is why Isaac started slowing down with 2 miles left to go.  I think that if he with just 10-15 less watts for those 2 hours, he likely wouldn’t have started slowing down and could have had a slightly better race time by a minute or so.

Another thing I want to point out is the Horizontal power ratio.  You can see it bounces around between 75% to 77% for the majority of the race.  It starts dropping significantly in the last couple miles.  This helps show how not only did Isaac start producing less watts, he also was less efficient by producing a lower percentage of power that was actually propelling him forward.  This is seen in the Running Effectivess, or RE, (adjusted for NGP) on the column on the far right.  The higher the number, the more efficient Isaac ran.  You can see how after Isaac got to the point in the race where the crowds thinned a little (mile 3 to 4), his RE was typically 0.97 to 1.00.  It’s not until he got to mile 23 where we start seeing a consistently lower number, 0.95 or less.

You can see in the chart below how these things took a visible drop in the final 2-3 miles of the race:

In addition to that drop in pace, we start to see other details as to why he slowed down.

                                                              miles 4 – 21:                                      Miles 22-26.2

stride length                                      0.70 meters                                           0.63 meters

Ground Contact Time:                       215 milliseconds                                 232 milliseconds

LSS/Kg                                                     0.138                                                   0.136

vertical oscillation:                              7.3 cm                                                  7.2 cm

Vertical Ratio:                                       0.104                                                     0.114

Cadence:                                          178 steps per minute                            174 steps per minute


In the end, it was a still a 7 minute PR for Isaac for the marathon distance!

As you can see, the amount data and insight from the Stryd device is insane.  It really helps me as a coach figure out what went wrong (or right) in a race (or training session).  Moving forward with Isaac, we will be working on decreasing his vertical oscillation (which will increase his horizontal power ratio) and improve his LSS by incorporating some plyometrics into his running routines.


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