RELATIONSHIP BETWEEN HAMSTRING FLEXIBILITY GAINS AND REDUCTION IN STRETCH-RELATED DISCOMFORT FOLLOWING DIAPHRAGMATIC BREATHING-BASED FLEXIBILITY TRAINING IN AMATEUR ATHLETES: A SECONDARY ANALYSIS

Abstract

Background
Changes in flexibility are commonly reported as gains in joint range, yet the athlete’s tolerance of
stretching is an equally important clinical outcome. Hamstring range can increase through
mechanical, sensory, neuromuscular, and postural influences, while the discomfort perceived near
the end of a stretch may affect how much range an athlete can use comfortably. Diaphragmatic
breathing has potential relevance because it can be integrated into stretching while also influencing
respiratory control, trunk stabilization, and relaxation. The present secondary analysis examined the
relationship between objective hamstring flexibility gain and reduction in stretch-related discomfort
using data from an experimental study in amateur athletes.
Objective
To determine whether improvement in Active Knee Extension (AKE) is associated with reduction in
Numeric Pain Rating Scale (NPRS) scores during stretching, and to compare the pattern of objective
and subjective improvement between athletes receiving diaphragmatic breathing plus flexibility
training and those receiving flexibility training alone.
Methods
Data from 60 amateur athletes aged 18–30 years were analyzed. Group A (n=30) received
diaphragmatic breathing exercises in addition to traditional stretching and flexibility exercises,
whereas Group B (n=30) received the same traditional flexibility program without the breathing
component. Average bilateral AKE and NPRS during stretching were recorded before and after
intervention. Within- and between-group changes were evaluated using paired and independent t-
tests. Pearson correlation examined the relationship between AKE improvement and NPRS reduction
and also explored whether age or weekly training frequency was related to flexibility gain. Statistical
significance was set at p<0.05.
Results
Average AKE gain was 11.80 ± 2.28° in Group A and 6.86 ± 2.29° in Group B (t=8.369, p<0.001;
Cohen d=2.16). NPRS reduction was 3.37 ± 0.69 points in Group A and 2.08 ± 0.54 points in Group
B (t=8.045, p<0.001; Cohen d=2.08). Across all 60 participants, flexibility gain showed a moderate
positive association with reduction in stretching-related discomfort (r=0.521, p<0.001). Age was not
significantly associated with AKE improvement (r=0.138, p=0.2944), and weekly training frequency
showed essentially no relationship with AKE change (r=-0.008, p=0.9487). Clinically meaningful
improvement, defined in the source study as an AKE gain of at least 8°, occurred in 96.7% of Group
A and 26.7% of Group B.
Conclusion
Greater gains in hamstring flexibility were accompanied by greater reductions in stretch-related
discomfort. The stronger objective and subjective response in the diaphragmatic breathing group
suggests that breathing-based flexibility training may influence not only the range achieved but also
the athlete’s tolerance of stretching. These findings support evaluating flexibility and stretch
discomfort together rather than relying on range of motion alone.