DOES HAMSTRING TIGHTNESS LEAD TO INCREASED SPINE FLEXION IN A MAXIMUM DOWNWARD REACH?

Participants: J. A. Ashton-Miller, L. J. Huston, P. Moga, E. M. Wojtys

Keywords: spine, biomechanics, motion analysis, hamstrings

Introduction

The hamstring muscles, by virtue of their origin and insertion, can affect trunk mechanics during activities of daily living. This study compares the thoracic and lumbar spine flexion occurring during a maximum downward reach test in subjects with and without tight hamstrings. We hypothesized that in reaching for the floor with straight knees, subjects with tight hamstrings flex their thoracic and lumbar spine more than normal, due to restricted hip flexion.

Materials and Methods

Seventeen subjects (7 males, 10 females, avg. age 20.7 + 9.8 yrs) diagnosed with tight hamstrings were compared with a healthy age-matched control group of 14 subjects (8 males, 6 females). For the purposes of this study, tight hamstrings were diagnosed in those who, while without bending their knees, were unable to touch the ground with their fingertips during a maximum downward reach test. Patient history and general anthropometric measurements were taken on all subjects. Pairs of specially-designed passive retroreflective markers were affixed to the subjects' skin at four spine landmarks: T1, T10, L3, and S1, while reflective tape markers were applied to the skin over the PSIS, ASIS, greater trochanter, lateral femoral condyle, and the lateral epicondyle of the elbow. Each spine marker consisted of a semicircular- shaped spring wire frame, which was mounted in the mid-sagittal plane over each of the spinal landmarks. Two feet pivoted at each end of the frame, so that they could be taped to the skin above and below the landmarks. Each pair of retroreflective markers were spaced 6 cm apart on a cardboard strip. The rectangle was mounted at the midpoint of each frame such that a line through them was always maintained normal to the skin surface at the landmark. Marker reliability studies were performed on subjects using A-P and lateral radiographs in order to confirm correct marker placement and behavior.

The subjects were instructed to perform two unconstrained maximum downward reach tests, starting in the upright position and each taking 15 seconds to complete. Marker trajectories were measured using a laterally placed 2-D motion analysis system (MacReflex; Qualisys, Glastonbury, CT), at a sampling rate of 120 Hz. T1-T10, T10-L3, L3-S1, and pelvis-knee angles were calculated in the mid-sagittal plane at each time point. To facilitate inter subject comparisons, final finger-to-floor distance was normalized by initial finger-to-floor distance in the upright stance, yielding the normalized reach distance, D.

Multiple linear regression models were used to predict D from known changes in thoracic angle (x1), lumbar angle (x2) and hip flexion angles (x3) by group. Unpaired Student t-tests were used to determine differences between the normal and tight hamstring groups. Statistical significance was determined to be at the p<0.05 level.

Results

No significant differences were found in initial spine or hip angles between the two groups (Table I). Multiple regression analysis showed that in a maximum downward reach task, D is primarily determined by hip flexion angle in both normal and tight hamstring groups.

Normal Flexibility group:

D = 0.005(x1) - 0.002(x2) + 0.010(x3) r2 = 0.950

x1: p =0.197; x2: p=0.574; x3: p=0.008

Tight hamstrings group:

D = - 0.008(x1) + 0.002(x2) +0.010(x3) r2 = 0.950

x1: p =0.087; x2: p =0.209; x3: p =0.005

Both D and change in x3 were significantly greater in the control group than in the tight hamstrings group (Table 1). The fact that x3 was less than 60° in the tight hamstring group confirms the initial diagnosis. The thoracic (T1-T10) angle in the fully flexed position was significantly greater in the control group (p=0.05), while the lower thoracic/upper lumbar (T10-L3) angle was greater in the tight hamstrings group. The lower lumbar angle (L3-S1) in the fully flexed state was significantly lower in the tight hamstring group than in the healthy control group (p=0.03).

Table 1:

Mean (SD) of Thoracic, Lumbar and Hip Flexion Angles(°)

* statistically significant

Conclusions

In the tight hamstring group, maximum downward reach (D) was not associated with increased flexion of the thoracic spine. It was, however, associated with an increase in T10-L3 angle and a significant decrease in the L3-S1 angle. These patients therefore compensated for their tight hamstrings by employing increased lower thoracic/upper lumbar flexion, even though they were not able to reach down as far as the healthy control group.

If this finding is confirmed by others, it remains to be shown that lower thoracic/upper lumbar compensation is associated with Scheuermann's changes and/or low back problems in this region of the spine.