The fruits of ones labor: Effort-reward imbalance but not job strain is related to heart rate variability across the day in 35-44-year-old workers.

This paper is interesting because multilevel growth curve models were used to demonstrate that age modifies work stress-heart rate variability (HRV) associations. Middle-aged workers had the most pronounced inverse association between HRV and effort-reward imbalance, a result which is in line with what you see as an occupational health physician engaged in stress management.

Cross-sectional data were used to evaluate associations of the Demand Control Model and the Effort Reward Model, respectively, and HRV. A total of 591 workers were grouped in four different age groups (17-34, 35-44, 45-54, and 55-65 years). Multilevel growth curve models were used to examine whether age modifies a potential association between work stress and HRV. The analysis is rather advanced, but the use of repeated measures of HRV asks for a multilevel analysis. The results are therefore seen as strong evidence for an interactive effect of age when it comes to the association between work stress and HRV. It is interesting that no associations were found between the Demand Control Model and HRV, contrary to associations between the Effort Reward Model and HRV. This indicates that the two most used stress models do quantify different issues in connection with work stress. Associations between HRV and the Demand Control Model have, however, been demonstrated, but studies on the subject are few {1-3}. The result presented in this paper -- that the inverse association between effort-reward imbalance and root mean square successive difference (RMSSD) is most pronounced in the middle-aged compared to younger and older study participants -- underlines the importance of the circumstances. The circumstances are always of importance to the perception of stressors, and circumstances have to be considered when you study stress physiology, discuss relevant stressors or want to make interventions or stress management. In this case, age was of importance and, in other cases, social status or other psychosocial factors, genetics or personality may influence the significance of working conditions in stress physiology {4}.

References:
{1} Chandola et al. Neurosci Biobehav Rev 2010, 35:51-7 [PMID:19914288].
{2} Clays et al. Int Arch Occup Environ Health 2010, May 1, Epub ahead of print [PMID:20437054].
{3} Collins et al. Am J Ind Med 2005, 48:182-93 [PMID:16094616].
{4} Bergman et al. Int J Behav Med 2008, 15:54-61 [PMID:18444021].