Altitude training and haemoglobin mass from the optimised carbon monoxide rebreathing method determined by a meta-analysis

Abstract

Objective: To characterise the time course of changes in haemoglobin mass (Hbmass) in response to altitude exposure.

Methods: This meta-analysis uses raw data from 17 studies that used carbon monoxide rebreathing to determine Hbmass prealtitude, during altitude and postaltitude. Seven studies were classic altitude training, eight were live high train low (LHTL) and two mixed classic and LHTL. Separate linear-mixed models were fitted to the data from the 17 studies and the resultant estimates of the effects of altitude used in a random effects meta-analysis to obtain an overall estimate of the effect of altitude, with separate analyses during altitude and postaltitude. In addition, within-subject differences from the prealtitude phase for altitude participant and all the data on control participants were used to estimate the analytical SD. The 'true' between-subject response to altitude was estimated from the within-subject differences on altitude participants, between the prealtitude and during-altitude phases, together with the estimated analytical SD.

Results: During-altitude Hbmass was estimated to increase by ∼1.1%/100 h for LHTL and classic altitude. Postaltitude Hbmass was estimated to be 3.3% higher than prealtitude values for up to 20 days. The within-subject SD was constant at ∼2% for up to 7 days between observations, indicative of analytical error. A 95% prediction interval for the 'true' response of an athlete exposed to 300 h of altitude was estimated to be 1.1-6%.

Conclusions: Camps as short as 2 weeks of classic and LHTL altitude will quite likely increase Hbmass and most athletes can expect benefit.

Keywords: Altitude; Statistical review.

Figure 1

Estimates of the change in haemoglobin mass (Hbmass) during live high train low (LHTL, n=24) and classic (n=16) altitude exposure. Fitted lines are for the linear and quadratic models. Dashed lines are the upper and lower 95% confidence limits of the quadratic model. The relative weightings of estimates are indicated by symbol size and border thickness—the largest symbols are for the highest weighted estimates, the estimates with the smallest SEs. †The study at 1360 m, and has been omitted from the reported analyses.

Figure 2

Estimates of the change in haemoglobin mass (Hbmass) after live high train low (LHTL, n=15) and classic (n=21) altitude exposure. The relative weightings of estimates are indicated by symbol size and border thickness—the largest symbols are for the highest weighted studies which have the smallest SEs. †Outliers, the estimate at day 4 from Frese and Friedmann-Bette, and the estimate at day 7 from Neya et al. ‡The other three estimates from Frese and Friedmann-Bette (classic altitude and filled triangles) omitted from the reported analysis. Dotted (≤20 days) and dashed (>20 days) lines are the modelled estimates indicated in table 3.

Figure 3

Estimates of the within-subject coefficient of variation (CV (%)) of haemoglobin mass (Hbmass) obtained using all of the pairwise differences in natural log of Hbmass (ln(Hbmass)) over time from the 17 studies using either repeated measures on control participants or the prealtitude replicates on the altitude participants. A total of 80 estimates were obtained from 1003 paired differences. Three studies provided 51 estimates as a consequence of frequent serial measures on their control participants and duplicate measures at baseline on their altitude participants: Garvican et al (n=25), Robertson et al (n=12) and Saunders et al (n=14). The lower panel is a repeat of the upper panel expanding the first 40 days, with the symbol sizes indicating how many pairwise observations (on individuals) were used to generate the estimate; a small symbol indicates ≤7 observations, a medium symbol 8–14 observations and a large symbol ≥15 observations. A dashed line on both panels shows the fitted models; for x (days) ≤7whereas for x >7 Superscripted symbols indicate studies with the five largest estimates, each of which was >4%; ^‡Frese and Friedmann-Bette, §Garvican et al and ^†Saunders et al.

Figure 4

Estimated median and estimated between-subject ‘true’ change in haemoglobin mass (Hbmass) in response to altitude exposure. The solid line refers to the same quadratic model as in figure 1 with dashed lines being the upper and lower 95% individual response limits. Where the lower limit of the individual responses was estimated to be negative, it has been truncated at zero.