1) The document discusses tools for analyzing power data from bike powermeters, including power profiling, normalized power, training stress score, and quadrant analysis. 2) It defines normalized power as an estimate of the power a rider could maintain if power was constant, rather than variable as with most rides and races. The calculation involves smoothing the power data, raising it to the 4th power, and taking the average. 3) Normalized power provides a valid way to compare training sessions and races with different demands, and can be used to assess fitness changes without formal testing by examining normalized power from hard one-hour races.

1. Making sense out of apparent chaos:
analyzing data from on-bike
powermeters
Andrew R. Coggan, Ph.D.
Cardiovascular Imaging Laboratory
Washington University School of Medicine
St. Louis, MO 63021

2. On-bike powermeters: both a blessing and a curse
Powermeters provide a
detailed (e.g., second-bysecond) record of a
cyclist’s power, cadence,
heart rate, etc., during
each training session or
race, but...
1. Multiple variables/seconds x 3600 seconds/hour x
several hours/day x 365 days/year = a LOT of data!!

3. 2. Data are highly variable!

4. “Tools” for analyzing powermeter data
1)
2)
3)
4)
Power profiling
Normalized power
Training stress score
Quadrant analysis

5. “Tools” for analyzing powermeter data
1)
2)
3)
4)
Power profiling
Normalized power
Training stress score
Quadrant analysis

6. What is normalized power?
Normalized power is an estimate of the power
that a rider could have maintained for the same
physiological “cost” if power had been perfectly
constant (e.g., as on an ergometer) instead of
variable.

7. Average power =
273 W

8. Kinetics of PCr resynthesis
Coggan et al., J Appl Physiol 1993; 75:2125-2133

9. Half-lives of other physiological responses
Power (force and/or velocity)
(0 s)
PCr kinetics
~25 s
Heart rate/cardiac output:
~25 s
Sweating:
~25 s
VO2:
~30 s
VCO2:
~45 s
Ventilation:
~50 s
Temperature (core):
~70 s

11. Data smoothed using 30 s rolling ave.

12. VO2, heart rate, lactate, and RPE
as a function of power output
VO2
Blood lactate
RPE
Heart rate
180
8
160
7
140
VO2max
6
120
5
100
4
80
3
OBLA
60
40
2
Lactate threshold
1
0
0
50
100
150
200
250
Power (W)
300
350
400
20
0
450
HR (beats/min)
VO2 (L/min), lactate (mM), or RPE
(U)
9

13. Blood lactate-exercise intensity relationship
20
y = 3.94x3.91
R2 = 0.81
Blood lactate (mmol/L)
18
16
14
12
10
8
6
4
2
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Power/power at lactate threshold
Coggan, unpublished observations

16. Steps to calculate normalized power
1) smooth the data using a 30 s rolling average to
take into account the time course of physiological
responses
2) Raise the data obtained in step 1 to the 4th power
take into account the non-linear nature of
physiological responses
3) take the average of the values obtained in step 2
4) reverse step 2 to obtain the normalized power

17. Normalized
power = 301 W

18. Relationship of average and normalized power to
maximal steady state power
Average power
Normalized power
Power during ~1 h race (W)
500
400
y = 0.93x + 27
R2 = 0.93
300
y = 1.27x - 126
R2 = 0.73
200
100
0
0
100
200
300
400
500
Maximal steady state power (W)
Coggan, unpublished observations

19. Normalized power for 1 h (W)
Relationship of normalized power to power at lactate
threshold (Dmax method)
500
400
y = 0.88x + 51
R2 = 0.91
300
200
100
0
0
100
200
300
400
500
Power at lactate threshold (Dmax method) (W)
Edwards et al., unpublished observations

20. Advantages of/uses for normalized power
• Allows more valid comparison of races or training
sessions with differing demands
– e.g., hilly vs. flat training rides, criteriums vs. TTs, outdoor vs.
indoor training
• Helpful in the design of novel interval workouts
– if normalized power for session (intervals plus recovery periods
combined) exceeds athlete’s power-duration curve, unlikely that
they will be able to complete workout as planned

21. Advantages of/uses for normalized power (con’t)
• Can be used to assess changes in fitness w/o need for
formal testing
– normalized power from hard ~1 h race provides estimate of
maximal steady state power
• May prove to be useful constraint when attempting to
model performance
– e.g., to determine optimal TT pacing strategy

22. Limitations of normalized power
• Essentially assumes that the net contribution from
anaerobic ATP production is negligible
– therefore not valid during shorter efforts in which contribution
from anaerobic capacity is significant (e.g., individual pursuit)
• Occasionally overestimates sustainable power
– is the algorithm biased, or are such data just statistical outliers?