Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2024 Jul 20;11(7):736.
doi: 10.3390/bioengineering11070736.

Differential Back Muscle Flexion-Relaxation Phenomenon in Constrained versus Unconstrained Leg Postures

Yi-Lang Chen  1 , Ying-Hua Liao  1   2
Affiliations

Differential Back Muscle Flexion-Relaxation Phenomenon in Constrained versus Unconstrained Leg Postures

Yi-Lang Chen et al. Bioengineering (Basel). .

Abstract

Previous studies examining the flexion-relaxation phenomenon (FRP) in back muscles through trunk forward flexion tests have yielded inconsistent findings, primarily due to variations in leg posture control. This study aimed to explore the influence of leg posture control and individual flexibility on FRP in back and low limb muscles. Thirty-two male participants, evenly distributed into high- and low-flexibility groups, were recruited. Activities of the erector spinae, biceps femoris, and gastrocnemius muscles, alongside the lumbosacral angle (LSA), were recorded as participants executed trunk flexion from 0° to 90° in 15° increments, enabling an analysis of FRP and its correlation with the investigated variables. The findings highlighted significant effects of all examined factors on the measured responses. At a trunk flexion angle of 60°, the influence of leg posture and flexibility on erector spinae activities was particularly pronounced. Participants with limited flexibility exhibited the most prominent FRP under constrained leg posture, while those with greater flexibility and unconstrained leg posture displayed the least FRP, indicated by their relatively larger LSAs. Under constrained leg posture conditions, participants experienced an approximate 1/3 to 1/2 increase in gastrocnemius activity throughout trunk flexion from 30° to 90°, while biceps femoris activity remained relatively constant. Using an inappropriate leg posture during back muscle FRP assessments can overestimate FRP. These findings offer guidance for designing future FRP research protocols.

Keywords: flexibility; flexion–relaxation phenomenon; leg posture; muscle activity; trunk flexion.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Schematic of criteria for determining individual flexibility.
Figure 2
Figure 2
Flowchart depicting the selection process for the two test groups enrolled in the study.
Figure 3
Figure 3
Schematic illustration demonstrating the testing posture, body angles during trunk flexion, and positions of markers and stickers on the participant’s body.
Figure 4
Figure 4
Lumbar erector spinae (LES) activities across different trunk flexion angles, with comparisons using independent t-tests between two leg postures (LP) for each flexibility group.
Figure 5
Figure 5
Leg muscle activities across various trunk flexion angles between the two leg postures (LP), with comparisons using independent t-tests for gastrocnemius electromyography.
Figure 6
Figure 6
Comparisons of lumbosacral angles (LSAs) for four test combinations comprising two flexibility levels and two leg postures (LP).
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Keyserling W.M. Workplace risk factors and occupational musculoskeletal disorders, part 1: A review of biomechanical and psychophysical research on risk factors associated with low-back pain. Am. Ind. Hyg. Assoc. J. 2000;61:39–50. doi: 10.1202/0002-8894(2000)061<0039:WRFAOM>2.0.CO;2. - DOI - PubMed
    1. Shin G., D’souza C., Liu Y.H. Creep and fatigue development in the low back in static flexion. Spine. 2009;34:1873–1878. doi: 10.1097/BRS.0b013e3181aa6a55. - DOI - PubMed
    1. Baril-Gingras G., Lortie M. The handling of objects other than boxes: Univariate analysis of handling techniques in a large transport company. Ergonomics. 1995;38:905–925. doi: 10.1080/00140139508925159. - DOI - PubMed
    1. Shin G., Shu Y., Li Z., Jiang Z., Mirka G. Influence of knee angle and individual flexibility on the flexion–relaxation response of the low back musculature. J. Electromyogr. Kinesiol. 2004;14:485–494. doi: 10.1016/j.jelekin.2003.12.001. - DOI - PubMed
    1. Plamondon A., Delisle A., Bellefeuille S., Denis D., Gagnon D., Larivière C., IRSST MMH Research Group Lifting strategies of expert and novice workers during a repetitive palletizing task. Appl. Ergon. 2014;45:471–481. doi: 10.1016/j.apergo.2013.06.008. - DOI - PubMed

LinkOut - more resources