MethodsObjective

Introduction

Figures

Significance

References1. Andersson, G.B., Epidemiologic aspects on low-back

pain in industry. Spine, 1981. 6(1): p. 53-60. 2.2. Radebold, A., et al., Muscle response pattern to

sudden trunk loading in healthy individuals and in patients with chronic low back pain. Spine, 2000. 25(8): p. 947-54. 3.

3. Marshall, P.W., I. Desai, and D.W. Robbins, Core stability exercises in individuals with and without chronic nonspecific low back pain. Journal of strength and conditioning research / National Strength & Conditioning Association, 2011. 25(12): p. 3404-11. 4.

4. Moreau, C.E., et al., Isometric back extension endurance tests: a review of the literature. Journal of manipulative and physiological therapeutics, 2001. 24(2): p. 110-22.

5. Alaranta, H., et al., Static back endurance and the risk of low-back pain. Clin Biomech (Bristol, Avon), 1995. 10(6): p. 323-324.

6. Feldman, D.E., et al., Risk factors for the development of low back pain in adolescence. American journal of epidemiology, 2001. 154(1): p. 30-6. 7.

7. Russ, D.W., Sex Differences in Muscle Fatigue, in Human Muscle Fatigue, C.a.R. Williams, S., Editor 2009, Routledge: New York. p. 135-163.

Data Analyses

A three way mixed-model MANOVA was used to determine the effects of load magnitude (20, 40, or 60% MVIC), group (healthy, LBP) and sex (female, male) on time to task failure (TTF), slope of median frequency of each muscle.

Median power frequency (MPF) was determined using a Fast-Fourier transformation and was calculated for one second epochs during the fatigue trials with a 50% overlap using custom software developed in MatLabTM .

Low back pain (LBP) is a common problem, affecting as much as 80% of the population at some point [1]. It has been suggested that coordinated trunk muscle activity, particularly in the lower back, may play a critical role in preventing back pain by providing spinal stability [2, 3]. While considerable data are available regarding the role of the strength and endurance of the trunk extensors in LBP [4, 5], less is known about the trunk flexor muscles. As contributors to spinal stability, these muscles may also play an important function in preventing back pain.

To examine the link between the trunk flexors and LBP by measuring the abdominal endurance and muscle activity of two groups of subjects, those with LBP and healthy controls.

Our study suggests that therapists should not train trunk flexor endurance as a means of improving back pain, as it is unlikely that LBP affects trunk flexor muscular endurance (excluding perhaps the left and right rectus abdomini) to begin with.

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Discussion

Figure 4. Normalized slope of MPF for the rectus abdominus, external and internal obliques.

• Participants with a history of LBP do not have a significant loss in abdominal endurance versus healthy controls [1, 6].

• Raises questions regarding the role of the trunk flexor muscles in low back pain.

• To our knowledge, this is the first study to compare trunk flexor muscle endurance in females and males, and confirms studies on the appendicular and back extensor muscles, showing that females have greater fatigue resistance in females than males at higher loads [7].

• Interestingly, this difference disappeared in the LBP group.

Figure 2. TTF of participants with and without LBP at each level of effort

The Influence of Previous Low Back Pain and Sex on Trunk Flexor Endurance at Various Work LoadsLauren C. Thomas, Seth Oberst, DPT, Christopher Wall, DPT, Lindsey Russell, BS, Kerry McFadden, BS, David Russ, PT, PhD, Brian Clark, PhD, James S. Thomas, PT, PhD.Ohio University, Athens, OH, USA.

Time to Task Failure in Control vs LBP Populations

Percent MVIC

20% MVIC 40% MVIC 60% MVIC

Tim

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Control PopulationLBP Population

Time to Task Failure in Female vs Male Populations

% MVIC

20% MVIC 40% MVIC 60% MVIC

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(s)

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Female Population Male Population

Subjects• 18 Hx of LBP (10 female, 8 male)• 18 Healthy controls(10 female, 8 male)• Average age: 22.5 ± 2.4 years• Average Ht: 67.6 ± 3.82 in• Average Wt: 157.0 ± 25.8 lbs

Procedure• Fatigue assessed at 20, 40, or 60% MVIC. • Testing sessions randomized and

separated 72 hours.• Surface EMG data were recorded

bilaterally from: 1) rectus abdominus 2) external oblique 3) internal oblique and 4) rectus femoris.

• Participants were positioned in supine on a segmented table in a neutral hip position (See Figure 1)

• Participants were then asked to maintain the trunk in a horizontal position (± 1 degree) as long as possible against a load equal to 20, 40, or 60% of MVIC.

• Task failure occurred when the participant was unable to maintain this position for 3 consecutive seconds.

Figure 1. Custom table used to assess trunk fatigue at various levels of effort.

Results• TTF decreased as task difficulty was increased

(F=76.5, p<0.05). • No effect of LBP history on task on TTF

• TTF with history of LBP was 87%, 78%, and 52% of healthy participants

• Main effect of gender on TTF (F=5.65, p<0.05)• Normalized MPF slope for Left and right

rectus abdominus (LRAB and RRAB) showed significant differences between the control and LBP participants at 40% of MVIC (p<0.05).

External Obliques Normalized Slope

% MVIC

20% MVIC 40% MVIC 60% MVIC

No

rma

lized S

lope -4

-2

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2Control Population LBP Population

Internal Obliques Normalized Slopes

% MVIC

20% MVIC 40% MVIC 60% MVIC

No

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lopes

-4

-3

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-1

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Rectus Abdomini Normalized Slopes

%MVIC

20% MVIC 40% MVIC 60% MVIC

No

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e -5

-4

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Figure 3. Effect of gender on TTF