As shown in , novice and expert practitioners did not differ on key variables that have been associated with inflammation. Seven women in each of the groups were postmenopausal. As a consequence of our stringent exclusion criteria, overall medication use was low; novices and experts did not differ in the proportion reporting use of aspirin, ibuprofen, or other over-the-counter analgesics, ps > .39, birth control pills, hormone replacement therapy, omega-3 supplements, or a daily multivitamin, ps > .23.
Mean (SD) demographic, physiological, dietary, and behavioral data for novice and expert yoga practitioners
Mean ratings of novices’ (21.92, SD=4.93) and experts’ (31.86, SD=4.83) ability to perform common yoga poses, assessed during the screening session, were clearly different, F(1,48) = 51.82, P < .000. Similarly, novices (M=31.88, SD=7.77) had substantially less hamstring and low back flexibility than experts (M=41.81, SD=5.19), producing the expected differences on the sit-and-reach test, F(1,49) = 27.91, P < .001.
Self-Report and Behavioral Data
There was a significant time by condition interaction for PANAS positive affect, F(4, 198) = 14.49, P < .001 (). Participants’ positive mood scores increased following yoga, decreased following the video, and were unchanged following movement.
Mean (± SEM) changes in self-reported positive affect on the PANAS as a function of time and condition. Experts and novices did not differ.
Due to a lack of variability in PANAS negative affect scores, values were dichotomized as “at the minimum” (n = 280, 62.36%) and “above the minimum” (n = 169, 37.64%). Logistic regression on the transformed values was conducted with Generalized Estimating Equations (GEEs) using an unstructured covariance matrix to account for the repeated visits. Results revealed a significant time main effect, X2(1) = 14.35, P < .001, and a significant time by yoga expertise interaction, X2(2) = 5.45, P < .02. Experts were more apt to report negative affect above the minimum at the end of the conditions than novices.
Stroop interference scores showed no differences for either the positive or negative emotion words as a function of time, expertise, condition, or their interactions, all Ps > .24. However, as illustrated by the heart rate increase (), the Stroop did function as a mild stressor.
Mean (± SEM) heart rate throughout the admissions as a function of novice vs. expert yoga practitioner status. * denotes P = .03.
Novices and experts did not differ in hours of sleep the night before the CRC visits, F(1,47.8) = 0.63, p = .43. However, after controlling for the previous night’s sleep, novices (M = 6.75, SD = .93) reported significantly fewer hours of sleep than experts (M = 7.24, SD =1.00) following the 6-hour days in the CRC, F(1,46) = 5.94, P = .02
Skin Barrier Repair
The speed of skin barrier repair following tape stripping did not differ as a function of expertise, condition, time, or their interactions, all Ps > .08.
Analysis of participants’ heart rates revealed significant main effects for time and condition, as well as significant interactions between time and yoga expertise, F(7, 247) = 3.97, P < .001, and time and condition, F(14, 359) = 15.47, P < .001. Comparisons were planned between novices and experts for heart rate during the stressor, as well as three values collected well into the condition. Using a critical p-value of .038, experts had lower heart rates than novices during the stressor, t = 2.30, P = .025 (); no other tested time points reached even an uncorrected level of significance, all P’s > .08. Additionally, the degree of change from the Stroop to the stressors differed between the expertise levels, t=2.16, P = .035, with novices exhibiting larger responses to the stressors than experts. For the time by condition interaction, a critical P-value of .025 was used to compare yoga to the other two activities at time points during and after the condition. Participants’ heart rate during the yoga condition was higher than when in the video condition 10 minutes into the intervention, t=9.61, P < .001, and lower than the video condition at the end of the intervention, t=3.05, P = .004; similarly, yoga was higher than movement 10 minutes into the condition, t=2.41, P = .02, and lower post-condition, t=4.96, P < .001. However, as planned in the experimental design, the overall mean heart rate during the yoga condition did not differ from that in the movement condition, P =.17.
Cortisol and Catecholamines
The significant time effect for cortisol reflected the normal diurnal fall across the morning as well as the usual post-lunch increase, F(6, 371) = 80.21, P < .001. There were no significant group or condition effects or interactions.
There was a significant condition by time interaction for norepinephrine, F(10, 318) = 8.08, P < .001. Similar to the heart rate data, participants’ norepinephrine response after 10 minutes of the yoga was significantly higher than the same interval in either the video, F(1,121) = 27.42, P < .001, or the movement condition, F(1,121) = 12.77, P < .001. Novices and experts did not differ in norepinephrine production, F(1, 46.1) = .34, P = .56. The significant time effect for epinephrine reflected a post-stressor peak value for the session, followed by a decrease through the conditions, F(5,341) = 12.62, P < .001. In addition, experts had higher overall levels of epinephrine than novices, F(1,48.5) = 8.26, P = .006, a surprising finding in view of the norepinephrine and heart rate data. Examination of raw data showed that 4 experts and 1 novice were outliers across time; comparisons between these individuals and the remainder of the sample showed significantly fewer hours of sleep prior to the three visits, F(1,49)=9.52, P=.003, but no differences in affect, other health behaviors, or inflammation.
Serum Cytokines and hsCRP
Experts had lower overall IL-6 serum levels than novices, F(1,45.7) = 4.98, P = .03. Indeed, novices’ average IL-6 values were 41% higher than those of experts (). Additionally, although the group effect did not reach traditional significance levels for either sIL-6r, F(1,43.5)=3.55, P =.07, or TNF-α, F(1,45.3)=2.25, P =.14, both were in the expected direction, with lower levels of inflammation in yoga experts compared to novices.
Mean (± SEM) serum IL-6 as a function of novice vs. expert yoga practitioner status also reflect significantly elevated levels of IL-6 post-intervention.
Significant time effects were observed for all serum cytokines, all Fs > 16, all Ps < .001. Specifically, we observed elevations in IL-6 at the sessions’ end compared to the following morning, t=12.40, adj. P < .001 (). For sIL-6r, levels were higher at the sessions’ end, t=4.90, adj. P < .001, and the next morning, t=6.11, adj. P < .001, compared to baseline. Although TNF-α did not increase at the sessions’ end, it did rise the following morning, t=4.76, adj. P < .001.
We assessed hsCRP once at baseline at each of the three visits; 43% of the values (n = 65) were below the assay’s detectable lower bound of .3 mg/dL, and thus hsCRP was dichotomized as undetectable/detectable. The logistic regression with GEEs analysis showed that the odds of a novice having a detectable hsCRP level were 4.75 times that of experts (β = −1.55, P = .009).
LPS-Stimulated Cytokine Production
The expertise by time interaction for stimulated IL-6 production, F(4,275) = 2.57, P < .04, is shown in . A planned comparison showed that experts produced less IL-6 in response to the stressors than novices (Mdiff = 26076, SEdiff = 13104), F(1,53.1) = 3.96, P = .05. No other time points approached significance (all P’s > .14). Stress-induced LPS-reactivity was significantly correlated with total serum IL-6, r=.33, P=.02.
Mean (± SEM) LPS-stimulated IL-6 production throughout the admissions as a function of novice vs. expert yoga practitioner status. * denotes P = .05.
In the condition by time interaction for TNF-α, F(8,268) = 2.03, P = .04, values obtained immediately following the stressor were lower in the yoga condition, compared to the video and movement conditions combined (Mdiff = .09, SEdiff = .04), F(1,133) = 2.29, P = .02. Values obtained immediately following the stressor were lower in the yoga condition, compared to the video and movement conditions combined (Mdiff = .09, SDdiff = .36), F(1,137) = 4.90, P = .03.
To identify individuals producing high vs. low levels of inflammatory markers across the assay battery, median splits were applied to the average baseline values of our six markers: serum IL-6, TNF-α, sIL-6r, and hsCRP, and LPS-stimulated IL-6 and TNF-α production. Individuals falling into the low or high category on each marker were given a score of 0 or 1, respectively, and the summed values were grouped into low (0 or 1), medium (2 or 3) or high (4–6). Novices and experts showed very different patterns, χ2(2)=13.91, P < .001 (); 60% of the novices were high producers compared to only 24% of experts, while 40% of experts were low producers and 0% of the novices.
Figure 6 The numbers of novices and experts falling into low, medium, or high inflammatory groups based on the number of assays on which they were above the baseline median values for serum Il-6, TNF-α, sIL-6r, and hsCRP, and LPS-stimulated IL-6 and TNF-α (more ...)