Effect of Moderate-Intensity Aerobic Training on Serum Relaxin Levels, Low Back Pain Intensity, and Core Muscle Performance in Low-Risk Pregnant Women

Document Type : Research Paper

Authors

1 North Khorasan Social Security Treatment Management, Samen Aeme Hospital, Bojnord, Iran.

2 Department of Exercise Physiology, Faculty of Sport Sciences, Ferdowsi University of Mashhad, Mashhad, Iran.

3 Department of Sport Sciences, Faculty of Humanities, Kosar University of Bojnord, Bojnord, Iran.

4 Department of Sport Sciences, Faculty of Humanities, Kosar University of Bojnord, Bojnord, Iran

10.22080/jaep.2026.30384.2236

Abstract

Objectives: The aim of this study was to investigate the effect of eight weeks of moderate-intensity aerobic training on serum relaxin hormone levels, low back pain intensity, abdominal muscle endurance, and back muscle strength in low-risk pregnant women.  
Methods: 29 pregnant women with first or second pregnancy were selected as an available sample. After the withdrawal of 4 participants in the early stages (before the pre-test and the start of the intervention), finally 24 participants completed the study and were randomly divided into experimental (n=13) and control (n=11) groups. The aerobic training program was performed at 40% to 75% of maximum heart rate for eight weeks. Necessary measurements and blood tests were conducted 24 hours before the start of the first training session and 48 hours after the last training session. Repeated-measures ANOVA as well as non-parametric Wilcoxon and Mann-Whitney U tests were used to compare the mean data
Results: Exercise training caused a significant increase in relaxin hormone (P = 0.001) and muscle endurance (P = 0.001) in the experimental group, but did not produce a significant change in low back pain index or back muscle strength. Low back pain intensity showed no significant change in the exercise group but significantly worsened in the control group (P = 0.013).
Conclusion: Regular aerobic training can be recommended as a safe strategy to increase serum relaxin, improve abdominal muscle endurance, and prevent the exacerbation of low back pain during pregnancy; however, to achieve a significant reduction in low back pain, it should be combined with specific strengthening exercises for the trunk and back muscles.

Keywords

Journal of Applied Exercise Physiology
Volume 21, Issue 42
May 2026
Pages 15-29

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History

  • Receive Date: 28 October 2025
  • Revise Date: 17 December 2025
  • Accept Date: 27 January 2026

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