Fig 1.
Example of the protocol for a male runner reaching stage 6.
Table 1.
Descriptive characteristics of the subjects.
Notation: mean ± SD.
Fig 2.
Locations of the accelerometers attached to the runners’ bodies.
For each location, an example signal of the total acceleration over three seconds is shown. Note that only one of the two tibia accelerometers is used in this study.
Table 2.
Overview of all features.
Fig 3.
Calculation of contact time from the vertical lower back acceleration.
The green and red dots indicate respectively starts and ends of foot-ground contact.
Fig 4.
Measured vs predicted VO2max values.
D = descriptive features, HR = heart rate features, ACC = accelerometer features. Points that are closer to the orange line, on which the measured VO2max equals the predicted VO2max, correspond to more accurate predictions.
Table 3.
Comparison of the four combinations.
Table 4.
Fixed-effect coefficients learned from the complete dataset.
Table 5.
Comparison of the two methods of Weyand et al.
Fig 5.
Evaluation of the second method of Weyand et al. using gender and as features.
Fig 6.
Total tibia acceleration of two similar subjects.
The two subjects have the same gender (G = 1 = female), a similar body mass (BM = 71.8 kg for subject 1 and 68.5 kg for subject 2), and a similar inverse heart rate in the warm-up stage ( = 0.00559 for subject 1 and 0.00557 for subject 2). While the value of the
feature is low for subject 1 (0.689), it is high for subject 2 (2.30). Consequently, subject 1 has a lower VO2max (33.14 ml ⋅ kg−1 ⋅ min−1) than subject 2 (41.71 ml ⋅ kg−1 ⋅ min−1).
Fig 7.
Explained variance (R2) of F4 when down-sampling the tibia acceleration to different sample rates.