Employees need to recover from work during off-job time to stay healthy and maintain well-being . Previous studies have shown that recovery occurring off-job time promotes employee well-being and better functioning at work the next day. For example, recovery is positively related to life satisfaction, the next day’s work engagement [3-4] and task performance .
However, previous studies might only tell half of the story. In the literature on recovery, researchers have mainly concentrated on recovery occurring after work in non-work contexts (external recovery). However, recovery from work can start during the work day in the work context (internal recovery). This aspect of recovery has little attention from researchers. One exception is a study  which found that internal recovery during the work day increased the possibility that employees started their next working day in an optimally recovered state. Therefore, it is important to fill this research gap in order to facilitate employees’ internal recovery even when facing high work pressures and workloads.
According to the conservation of resources (COR) theory [7-8], recovery from work occurs if employees replenish psychological, emotional and physical resources that are depleted during work, and they prevent further depletion of these resources after work. One way that recovery can be accomplished is by employees changing the demands of their job in relation to their job resources, also called job crafting [9-10]. Job crafting helps the employee gain resources and prevent the loss of resources [9-10]. In the current study we focus on the possibility that job crafting helps employees to maintain a state of internal recovery, and we explore a potential underlying mechanism and boundary condition in this relationship. Thus the study makes two main contributions to the literature.
First, to our knowledge, the effect of job crafting on internal recovery state is uncharted territory. Based on COR theory , we argue that by job crafting , employees can replenish and prevent further depletion of resources that are depleted during the workday. By maintaining adequate resources, these employees are less likely to experience ego depletion, a state in which there has been an exhaustion of resources needed to change behaviors or pursue goals . In turn, lower ego depletion positively impacts internal recovery state . In sum, the current study makes a contribution to the literature by empirically testing the effect of job crafting on internal recovery state, and by testing whether this association is mediated by ego depletion. The results of these analyses have implications for how employers and employees can facilitate employees’ recovery after work.
Second, in line with COR’s principle of the gain paradox, which proposes that resource gains become more important when resource loss circumstances are high , we assume that the positive effect of job crafting on internal recovery becomes more important when the individual is in high resource loss circumstances. More and more jobs are high pressure work environments that require high concentration and self-control. For most employees, self-control demands are a source of stress at work . Thus, in the current study, we use self-control demands as an indicator of resource loss circumstances. We test whether job crafting has a differential effect on employee internal recovery state for employees with high or low self-control demands. Our study strengthens our understanding of how people with different levels of self-control demands at work might benefit differently from job crafting in terms of internal recovery.
In summary, our hypothesis is that job crafting will predict internal recovery; this process will occur through lower ego depletion; and this mediating effect will be moderated by self-control demands. In addition, consistent with previous studies , we focus on fatigue and vigor as indicators of employees’ internal recovery state. Figure 1 summarizes the relationships tested in this study.
The Job Demands-Resource Model proposes that jobs are characterized by demands and resources. Job demands require employees’ sustained effort and are related to certain costs. By contrast, job resources reduce the effect of job demands and associated costs, making it easier to achieve work goals and personal development . However, researchers make a distinction between challenging and hindering job demands . Specifically, challenging job demands, such as workload and time pressure, positively affect work-related outcomes . Challenging demands require extra effort to meet, but they could lead to personal gain or growth when employees are able to surmount them . In contrast, hindering job demands, such as role ambiguity and emotional demands, are not conducive to accomplishing work goals and hinder optimal functioning .
Using Job Demands-Resources Model as a framework, Tims et al  propose that job crafting refers to the self-initiated changes that employees make in their own job demands and job resources to attain and/or optimize their personal or work goals. Further, Tims et al  propose four job crafting dimensions: (1) increasing structural job resources (i.e., mobilizing job characteristics that help to achieve work goals and develop the self, such as opportunities for development, autonomy, or skill variety), (2) increasing social job resources (i.e., mobilizing job characteristics in the relational sphere, such as seeking social support, supervisory coaching, or performance feedback), (3) increasing challenging job demands (i.e., creating access to job demands that require effort but are rewarding when attained; for example, starting new projects), and (4) decreasing the hindrance of job demands (i.e., making sure one’s work is less demanding, such as by ensuring the work is emotionally less intense).
Job crafting is not only a general behavior but a daily behavior . Previous research showed that job crafting contributes to building resources at work such as positive affect [21-22], self-efficacy, work meaningfulness  and work engagement . Further, job crafting could prevent resource loss by relieving burnout , decreasing exhaustion , and relieving negative affect .
Theoretical background and hypothesis development
COR theory [7-8] provides a theoretical foundation for understanding how job crafting affects vigor and fatigue. This theory suggests that individuals seek to gain resources such as social support, and to prevent the loss of resources such as energy. Resources such as support and energy help employees to better address environmental demands. According to COR theory, employees need to gain new resources or replenish consumed resources to recover from work.
Job crafting can potentially increase employees' important resources such as supervisor supports and social relations   , and reduce resource loss such as relieving fatigue and decreasing burnout . Thus, it is reasonable to argue that job crafting, as an important positive workplace behavior , can reduce various stress reactions and promote internal recovery. Below, we will use COR as the theoretical basis to develop hypotheses regarding the relationship between job crafting and an internal recovery state, as well as the mediating role of ego depletion and the moderating role of self-control demands in these associations.
Mediating effect of ego depletion
Ego depletion refers to a state in which there has been an exhaustion of resources for changing behaviors or pursuing goals [27-28]. Based on COR theory , individuals with greater resources are less vulnerable to exhaustion of resources. We propose that job crafting provides employees the opportunity to gain resources and reduce the loss of resources, and thus to be lower their risk of ego depletion.
Specifically, job crafting might prevent employee ego depletion in the following ways. First, employees who increase their job resources (structural job resources and social job resources) may be less likely to experience ego depletion at work. COR theory proposes that employees who possess resources are better equipped to handle stressful circumstances and are more likely to avoid problematic situations . In line with this proposition, increasing structural job resources and social job resources via job crafting enables employees to handle high job demands, leading to less ego depletion. In addition, job crafting protects employees from ego depletion and allows employees to have access to larger pools of resources that will protect them from strain. For example, previous studies demonstrated that job crafting is negative related to burnout and exhaustion [24-25].
Second, we expect that increasing challenging job demands also prevents employee ego depletion. Although challenging job demands require extra resources from employees, they do not necessarily cause a decrease in resources. This is because the positive emotions, self-efficacy and personal growth provided by challenging job demands are important resources for employees [29-30]. Challenging job demands do require extra effort but do not have an energy-depleting effect . For example, Crawford et al found that increasing challenging job demands contributes to lower levels of burnout. Similarly, increasing challenging job demands may relieve ego depletion by building resources such as positive affect , self-efficacy , work meaningfulness .
Third, reducing hindering job demands may help prevent ego depletion. Hindering job demands have a strong relationship with ego depletion . Decreasing hindering job demands allows employees to focus their efforts on core work tasks and to restore energy , which may prevent ego depletion. For example, employees may protect themselves from ego depletion via minimizing contact with people whose problems affect them emotionally. Further, previous studies revealed that decreasing hindering job demands is related to decreased burnout and exhaustion [24-25]. Taken together, this evidence leads us to we believe that employees who decrease hindering job demands via job crafting experience less ego depletion.
Previous findings provide initial support for the idea that job crafting can prevent employee resource depletion. For example, job crafting contributes to decrease burnout . Similarly, Petrou et al  reported that job crafting was related to low exhaustion. Thus, based on the theoretical considerations and previous research, we expect that employees’ daily job crafting will be negatively related to daily ego depletion at work.
Daily job crafting will be negatively related to daily ego depletion at work.
COR theory proposes that individuals who have fewer resources are more vulnerable to further resource loss and less capable of resource gain . In line with the proposition, employees who experience ego depletion at work have fewer resources to deal with any additional job demands and thus experience high fatigue and low vigor at the end of workday. For example, if employees are in the state of depletion at work, they would find subsequent job tasks more demanding and need more resources to overcome non-task distractions. In turn, employees have few resources left at the end of the workday and feel more fatigue and less vigor.
There is some initial evidence that supports the above view. Researchers have demonstrated that self-regulatory resource depletion induced by self-control negatively predicts end-of-day vigor and positively predicts end-of-day fatigue . Similarly, Lanaj et al  found that morning depletion diminished employees’ daily vigor. Taken together, these results suggest that there are conceptual and empirical reasons to predict that employees who experience ego depletion will feel more fatigue and less vigor at the end of the workday.
Daily ego depletion will be negatively related to end-of-day vigor (2a) and positively related to end-of-day fatigue (2b).
Combining the aforementioned arguments about the relationships between daily job crafting and daily ego depletion, and between daily ego depletion and vigor and fatigue at the end of workday, it might be expected that daily ego depletion would be a mediator in the relationship between job crafting at work and the resources available after work. In terms of COR theory, job crafting is a resource-gaining experience; the gain in resources lowers the risk of ego depletion and allows the employee to deal with additional job demands; and the employee has sufficient resources left at the end of the day. Based on this argument, we believe that the relationship between daily job crafting and vigor and fatigue at the end of workday is mediated by daily ego depletion.
Daily ego depletion will mediate job crafting’s association with (3a) vigor and (3b) fatigue at the end of workday.
Moderating effect of self-control demands
Self-control demands require employees to control their impulses (inhibiting spontaneous, impulsive response tendencies), resist distractions (resisting distractions evoked by task-irrelevant stimuli) and overcome inner resistance (overcoming inner dislikes, aversions or motivational inhibitions) . Previous studies demonstrated that when employees encounter more self-control demands, they are more likely to experience a depletion of limited self-control resources [27-28].
The gain paradox principle of COR theory proposes that resource gains become more important in the context of resource loss . In line with this principle, employees who experience high self-control demands benefit most from job crafting as a way to reduce ego depletion. Compared to employees with low self-control demands, employees who encounter high self-control demands are more likely to experience resource loss  and job crafting becomes more important for them. Consequently, employees with high self-control demands are more likely to engage in job crafting to change the level of job demands in relation to job resources, thus reducing ego depletion. On the basis of the aforementioned discussion, we proposed the following moderation hypothesis.
Self-control demands will moderate the negative relationship between job crafting and ego depletion, with the relationship being stronger when self-control demands are high.
Combining our previous two hypotheses on mediation and moderation, we also proposed the following moderated mediation hypothesis.
Self-control demands will moderate the indirect effect of job crafting on (5a) vigor and (5b) fatigue at the end of workday through ego depletion, with the indirect effect being stronger when self-control demands are high.