In the present study, we found that 8 weeks of supervised SBA led to a significant improvement in anxiety among individuals living with substance use disorder. Our findings align with previous investigations that have also shown positive results of structured physical activity (PA) programs on anxiety. For example, an 8-week structured exercise intervention has been demonstrated to reduce anxiety in individuals with methamphetamine dependence during the early phase of community rehabilitation treatment (Dolezal et al., 2013; Rawson et al., 2015). Our work further supports these observations, suggesting that the positive effects of exercise can extend to a larger spectrum of substance use. In addition, our study indicates that exercise exerts some positive effects on sleep quality, insomnia, and perceived level of stress, although these results were not statistically significant.
We primarily focused our attention on assessing the effects of exercise on anxiety and depression, as these parameters are crucial for monitoring the clinical and psychological conditions of abstinent individuals (Zweben et al., 2004) and predicting the recovery process (Zorick et al., 2010; Zweben et al., 2004). Drug use induces distinct neurobiological and physiological modifications associated with depression and anxiety (Zweben et al., 2004). For instance, after drug use, there is a persistent reduction in dopamine-D2 receptors and dopamine concentration in the striatum of individuals living with substance use disorder (Greenwood et al., 2011; MacRae et al., 1987). These neurochemical adaptations can impair the ability to respond to environmental-related reward stimuli, worsening abstinence symptoms (Greenwood et al., 2011). A decreased response to non-drug reward stimuli has been observed in the striatum of individuals living with substance use disorder (Greenwood et al., 2011). Notably, regular physical training has been shown to ameliorate dopamine D2 and D3 receptor deficits in the striatum of animals (MacRae et al., 1987), thereby alleviating post-exposure behavior in morphine-addicted mice (Miladi-Gorji et al., 2012), and reducing withdrawal symptoms associated with cocaine, morphine, and nicotine (Miladi-Gorji et al., 2012; Sanchez et al., 2013; Thanos et al., 2013). Exercise-induced dopaminergic stimulation seems to be particularly important in the early phase of drug withdrawal, while mechanisms related to the long-term regulation of dopaminergic and glutamatergic stimulation in the striatum, along with the enhancement of neuroplasticity in the reward circuitry, seem to mediate the effectiveness of training in an advanced phase or rehabilitation (Lynch et al., 2013). Furthermore, exercise leads to increased expression of Brain-derived neurotropic factor (BDNF) in different regions of the brain (Gomez-Pinilla et al., 2011). It has been shown to remodel the brain structure in depressed patients, promoting positive behavioral adaptations to environmental stimuli and improving brain neuroprocessing in these patients (Zhao et al., 2020).
Moderate PA has been shown to improve sleep quality, contributing to mitigate insomnia in the general population. This is significant since insomnia and poor sleep quality are prevalent among community polysubstance users and are associated with lower metacognitive abilities in these individuals (Manzar MD, Alghadir AH, Khan M, Salahuddin M, Hassen HY, Almansour AM, Nureye D, Tekalign E, Shah SA, Pandi-Perumal SR, 2022). In our study, we observed encouraging findings regarding the improvement of sleep quality in individuals living with substance use disorder undergoing structured SBA within a community treatment setting. However, the improvement in sleep quality did not reach statistical significance compared to the control group. The lack of significance concerning the effect of structured PA on insomnia and perceived stress in our study may be partly attributable to the low frequency of training adopted. Similar research has demonstrated that patients who participated in more exercise sessions during the 8-week intervention experienced a greater reduction in psycho-emotional symptoms compared to less adherent participants (Rawson et al., 2015). Thus, it can be speculated that a higher weekly frequency of training could have ensured more significant results on sleep quality and perceived stress. Finally, we believe that the positive findings from this study were largely warranted by the tight supervision and individualized, and training program delivered. Supervised exercise sessions tend to produce a higher attendance rates compared to home-based training, and have been associated with better outcomes in smoking cessation and the mitigation of withdrawal symptoms (Ussher et al., 2019; Williams et al., 2011).
The main limitation of this study is the relatively small sample size. This was unavoidable due to the need to exclude seriously diseased or uncooperative individuals, as well as subjects unfit to perform PA. Further studies with larger samples and/or including a control group would help strengthen the evidence obtained in our investigation. A larger sample would likely increase the statistical significance of the results recorded in the present study.
As a final consideration, it is essential to note that the present study was based on a sample of collaborative subjects with stable mental conditions, treated within a residential setting. While regular PA appears to produce positive effects on phyco-emotional status, varying the exercise type/intensity/frequency may result in different effects. Yet, factors as the stage of addiction, the type of drug consumed, the mental health status, and physical abilities of the population can influence the response to exercise interventions. Therefore, the findings gained in this study may not be generalizable to all individuals living with substance use disorder in other treatment contexts. The implementation of exercise interventions in terms of type, intensity, and frequency should be carefully pondered so to be tailored on individual subject’s needs.