نوع مقاله : مقاله پژوهشی
نویسندگان
1 دانشیار گروه فیزیولوژی ورزشی، دانشکده علوم انسانی، دانشگاه ایلام، ایلام، ایران.
2 استادیار گروه فیزیولوژی ورزشی، دانشگاه پیام نور، تهران، ایران.
3 کارشناسی ارشد فیزیولوژی ورزشی، دانشکده علوم انسانی، دانشگاه ایلام، ایلام، ایران.
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Extended Abstract
Background and Aim: The skeleton plays a fundamental role in body structure, protection, movement, mineral storage, and hematopoiesis. Bone health is influenced by numerous factors, including nutritional status, hormonal balance, and physical activity. Age-related decline in bone mass is an inevitable process, and advancing age represents one of the most significant non-modifiable risk factors for osteoporosis. Preventive strategies such as weight-bearing exercise, adequate calcium intake, and sufficient vitamin D levels are essential for maintaining bone integrity and reducing fracture risk.
Scientific evidence indicates that regular physical activities, particularly weight-bearing exercises, contribute to preventing metabolic disorders and bone density loss by reducing bone resorption, increasing bone tissue formation, and maintaining mineral balance. These protective effects stem from exercise’s ability to modulate endocrine systems and mechanical signaling in bone cells, ultimately leading to improved bone structure quality and strength. In addition to exercise type and intensity, emerging evidence suggests that the timing of exercise may influence metabolic and physiological responses, including those related to bone metabolism. Circadian rhythms regulate numerous biological processes, and growing research indicates that the body’s internal biological clock may determine the optimal time to maximize exercise-induced benefits. Sato et al. (2019) reported a significant association between time of day and the physiological benefits derived from exercise, highlighting that exercise timing can elicit distinct metabolic responses. As a non-photic environmental stimulus, physical activity can modulate circadian rhythms and potentially shift the phase of the biological clock. When performed at an appropriate time, exercise may enhance circadian synchronization and improve physiological adaptation.
Although animal studies have demonstrated that exercise performance, gene expression, and energy expenditure vary according to time of day, the influence of exercise timing on bone metabolism remains insufficiently investigated, particularly in human populations. Therefore, the present study aimed to examine the effect of endurance exercise timing on serum levels of selected bone metabolism markers in middle-aged women.
Materials and Methods: This study was an experimental research with a pre-test to post-test design and a control group, conducted in 2024. The statistical population consisted of women aged 40 to 50 years in Kermanshah city. From the aforementioned population, 45 individuals volunteered to participate following a call for participation. Of these, seven were excluded due to not meeting the study’s inclusion criteria, and two were excluded after the first blood draw due to diagnosed illnesses. The remaining 36 individuals were selected as the statistical sample and were randomly assigned to three groups of 12: a morning exercise group (10:00 AM), an evening exercise group (7:00 PM), and a control group. Participants were selected based on inclusion criteria of BMI 18-25 kg/m², absence of chronic diseases, and no use of supplements affecting bone metabolism. The exercise protocol lasted eight weeks with three 60-minute weekly sessions consisting of warm-up, prolonged aerobic exercise, circuit training (sit-ups, push-ups, jump rope, plank, and burpees), and cool-down. Intensity gradually increased from 55% to 70% of heart rate reserve, monitored using Polar H9 heart rate monitors. Fasting blood samples were collected before and after the intervention, and serum levels of bone alkaline phosphatase, vitamin D, parathyroid hormone, and calcitonin were measured using standard kits. Statistical analyses were performed using analysis of covariance (ANCOVA) to assess between-group differences while controlling for baseline values. Bonferroni post hoc test were applied where appropriate. Statistical significance was set at p<0.05.
Findings: Results showed no significant differences in anthropometric characteristics between study groups. Data analysis using Shapiro-Wilk and Levene’s tests confirmed normal data distribution and homogeneity of variances. Then, ANCOVA test revealed that significant between-group differences in serum alkaline phosphatase levels (p=0.003), and Bonferroni post-hoc test showed that this difference was primarily between the evening exercise and control groups (p=0.003). While the morning exercise and control group comparison was not statistically significant. No significant differences were observed for other bone metabolism markers: parathyroid hormone (p=0.49), calcitonin (p=0.72), or vitamin D (p=0.41) (Table 1).
Conclusion: The present study demonstrated that the timing of endurance exercise exerts differential effects on certain bone metabolism markers in middle-aged women. Specifically, evening exercise resulted in a significant increase in bone-specific alkaline phosphatase levels, a marker of bone formation, whereas morning exercise did not produce a similar effect. These findings suggest a potential stimulatory influence of evening exercise on the bone formation process.
In contrast, neither morning nor evening exercise significantly affected serum levels of vitamin D, parathyroid hormone, or calcitonin. The slight increase in vitamin D observed in the morning exercise group may have been influenced by greater sun exposure rather than a direct physiological effect of exercise timing.
Overall, these results indicate that some markers of bone metabolism—particularly those associated with bone formation—may be sensitive to the timing of exercise, while others appear to be more strongly influenced by external factors such as nutritional status, sunlight exposure, and individual physiological variability. These findings highlight the potential importance of considering exercise timing when designing interventions aimed at optimizing bone health. However, further research with longer intervention periods, stricter control of confounding variables, and careful monitoring of dietary intake and environmental factors is needed to clarify the underlying mechanisms and to establish practical recommendations.
Ethical Considerations: The study protocol was approved by the Ethics Committee of Ilam University (Approval ID: IR.ILAM.REC.1403.017).
Compliance with ethical guideline: All participants provided written informed consent after receiving full explanations about the research objectives and procedures. Confidentiality of participant data was strictly maintained, and voluntary withdrawal from the study was permitted at any stage.
Funding: This article is derived from a Master’s thesis at Ilam University, with research costs covered by personal funds.
Conflict of Interest: The authors declare no conflicts of interest regarding the publication of this article.
کلیدواژهها [English]
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