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The purpose of this study was to determine the changes in vertebral column height (VCH) of males and females, at every one-half mile, for a total walking distance of 3 miles.
Twenty males and twenty females between the ages of 21 and 40 years walked 3 miles on a treadmill maintaining a walking speed that the subject rated between 12 and 14 on Borg's rate of perceived exertion scale. Blood pressure, heart rate, and VCH measurements were taken initially and at each half-mile interval throughout the three-mile walk. Vertebral column height (VCH) was measured from the spinous process of C7 to S2 using a standard tape measure.
Significant differences existed in vertebral column height according to sex (F = 16.18; p < .05) and significant differences in vertebral column height at the different distances (F = 65.02: p < .0001). Significant changes occurred in the VCH between half-mile intervals only between 0.5 miles and 1.0 mile and between 1.0 mile and 1.5 miles during the walk. As found with a regression analysis, curvilinear relationship exists between the distance walked and VCH; with VCH decreasing throughout the distance of the walk.
Vertebral column height decreased in a curvilinear relationship throughout the distance of walking 3 miles in both males and females.
One of the most simplistic means of weight loss is walking. According to the American College of Sports Medicine (ACSM),1 Center for Disease Control and Prevention (CDC),2 Surgeon General of the United States,3 and the American Heart Association,4 the suggested recommendations for exercise are an accumulated 30 minutes of moderate physical activity three-to-five days weekly. An example of the CDC-ACSM criteria is brisk walking over uneven ground at 3-4 mph, for 10-15 minutes, 5-7 times per week.1 Using the Borg Scale, which is a 20-point scale system used to monitor exercise intensity,2 it was estimated that the rate of perceived exertion (RPE) for the average individual participating in brisk walking would fall between 12 and 18. Although walking, jogging, and running on normal ground surfaces or a treadmill have multiple physiological benefits, detrimental effects such as vertebral compression may occur as well.
Various studies have been conducted related to the vertebral column and loss of vertebral column height (VCH).5–17 Koeller et al16,17 stated that the mean water content of the disc decreases in a non-linear fashion in both the thoracic and lumbar regions (T9-S1) with increased age. Research has shown that disc height loss occurs with dynamic activities rather than with static loading,14,15 varies depending on position,8 results from different load placement,14 and occurs in a non-linear fashion with most of the compression occurring early in the activity.14 Various researchers have noted that compressive forces on the vertebral column lead to decreased disc height, reduced shock absorption capability, decreased elasticity of the disc tissue, and decreased vertebral flexibility, thereby, putting the vertebral column at risk for injury and ultimately resulting in decreased VCH.11,12
The average adult takes 5,000 to 10,000 steps daily, which amounts to 3-5 miles per day, respectively.18–20 Subsequently, information as to how the spine responds to walking this distance is important. Garbutt et al19 observed changes in overall body height in elite runners using a stadiometer and found overall body height decreased 3.26 cm after 15 minutes of running and 2.12 cm between 15 and 30 minutes of running. Garbutt et al19 may have assumed that only changes in spinal height occurred during running. Roush et al14 investigated changes in VCH in male runners over a distance of three miles and found a curvilinear relationship between distance and VCH. However, no studies have been conducted to assess changes in VCH during walking for a distance of three miles. The purpose of this study was to determine the changes in VCH of males and females, at every one-half mile, for a total walking distance of three miles.
The investigation was approved by the Investigational Review Board of A. T. Still University of Health Sciences - Mesa, Arizona Campus. Each subject was informed of the risks associated with the study and was required to sign a consent form. Twenty, healthy males (mean age: 26.83 years; height: 176.10 cm + 9.61; weight: 75.81 kg + 10.17; BMI: 24.90 + 3.00) and twenty, healthy females (mean age: 25.60 years; height: 167.04 cm + 6.19; weight: 64.60 kg + 6.87; BMI: 23.5 + 2.30) who routinely exercised at a moderate intensity at least three times a week volunteered to participate in this study. Subjects were excluded if they had back pain within the last month, any type of diagnosed scoliosis, or any medical condition that prevented them from walking at a moderate pace on a treadmill. The subjects were introduced to the testing procedures and instrumentation prior to data collection.
A pilot study was conducted to determine the reliability of the investigators as measurers. Both investigators with over 15 years of experience measured the VCH for a sample of twelve females and eight males. A standard tape measure was used to measure VCH. During data collection, the subject was standing and the investigator palpated the spinous process of C7.20 The investigator then palpated the location of S2.20 Using a standard tape measure, the investigator recorded the distance between C7 and S2 in centimeters. An Interclass Correlation Coefficient (ICC) was calculated to assess the reliability of the investigators. The ICC (2,2) for the first investigator was 0.98, and for the second investigator was 0.94.
Prior to data collection, subjects were instructed to receive at least six hours of sleep in the recumbent position the night prior to testing and to arrive within 90 minutes of arising from bed. During the initial visit, subjects completed a medical questionnaire. In addition, subject's height (cm), body mass (kg), resting heart rate (HR), blood pressure (BP) and rating of perceived exertion (RPE) was obtained. Body Mass Index (BMI) was calculated as the ratio of weight (kg) and the square of the subject's height (m).
Prior to walking, HR, BP, RPE, and VCH were obtained. The VCH measurements from spinous process of C7 and S2 were acquired using a standard measuring tape. The slope of the treadmill was set to zero. Subjects were instructed to walk “normally” at a pace that fell between 12 and 14 on the rating of perceived exertion (RPE) scale, signifying moderate intensity. At each half mile, up to a total of 3 miles, subjects stepped off the treadmill and their BP, HR, RPE and VCH was recorded. This data were collected to ensure that subjects were maintaining a walking speed within a 12 to 14 rating on RPE scale and exercising at a safe intensity.21
Means and standard deviations of heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were calculated according to sex. Means and standard deviations of VCH and changes in VCH between intervals were recorded for each 0.5-mile interval during the 3-mile walk. A repeated-measures analysis of variance was calculated for VCH at each one-half mile interval, with sex as an independent variable. Significance was accepted at p<.05. Confidence intervals were used to determine individual differences between intervals for each sex. A relationship between VCH and distance interval, and a regression equation using a polynomial for the variables, were also calculated for each sex. All statistical calculations were performed using the Statview Statistical Package 5.0 (Cary, NC).
Means, standard deviations, and 95% confidence intervals of VCH can be found in Figure 1. The results of the analysis of variance were that were significant differences existed in VCH according to sex (F = 16.178; df = 1,38; p <.05). Significant differences also existed in VCH at the different distances (F = 65.02; df = 5,190; p <.05). No significant interactions were found between sex and distance (F = 0.51; df = 1,5; p > 0.05). Differences in VCH were noted to be significant between interval distances of onemile or greater, up until mile two; thereafter, no significant changes were seen. Significant changes occurred in the VCH between half-mile intervals only between 0.5 miles and 1.0 mile and between 1.0 mile and 1.5 miles during the walk.
A regression analysis was also calculated to determine the change in the means of the VCH of both males and females throughout the 3-mile walk. A regression plot for a seconddegree polynomial is shown in Tables 1. Coefficients of determination were calculated between the regression equation and the actual data points. The coefficients were 0.98 and 0.99 for males and females, respectively. The regression plot indicates that a curvilinear relationship exists between the distance walked and VCH. The VCH decreased throughout the distance of the walk.
Mean changes in VCH can be found in Table 2. Overall, the maximum decrease in VCH was 1.14 cm for males (F = 2.36; df = 5,19; p <.05) and 1.10 cm for females (F = 2.34; df = 5,19; p <.05). Males exhibited changes in VCH during each interval of walking, with a maximum amount of change in VCH of 0.33 cm between 1.0 and 1.5 mile (Figure 2). The average decrease between intervals was 0.25 cm + 0.07.
Females exhibited significant decreases in VCH for each interval up to 2.0 miles, with a maximum amount of change between .05 and 1.0 mile of 0.33 cm (Figure 3). The average decrease between intervals up to 2.0 miles was 0.09 cm + 0.11. Changes in VCH from 2.0 to 2.5 miles and from 2.5 to 3.0 were not significantly different from zero.
Previous investigators have concluded the VCH will decrease in height during physical activity.13,21 The purpose of this study was to determine if VCH changed and how it changed when walking a distance of 3 miles. Americans are walking greater distances in order to achieve health and weight loss benefits as marketed by the American Heart Association,4 America on the Move,22 and the 10,000 steps program.23 The overall change in VCH was relatively small (males = 1.14 cm; females = 1.10) when compared to the changes in overall body height in running.19
The data indicate that the VCH decreased in a curvilinear fashion over the distance walked in both males and females. It is assumed that the changes in VCH are due to the compressive forces that are placed on the disc and resultant hydrostatic changes that occurred as a result of the load. Holm et al24 found that as hydration decreased, pressure on the disc was increased. As water content decreases so does the height of the disc; the result is a decrease in total vertebral column height.
Interestingly, no changes were shown to occur during the first half-mile walked. It could be hypothesized that the loading forces were not enough at this point to cause hydrostatic changes within the intervertebral disc. Koeller et al16,17 found that the mean water content of the disc decreases in a non-linear fashion in both the thoracic and lumbar regions (T9-S1) with increased age and that when subjected to the same compressive load, the intradiscal pressure was greater in the upper lumbar discs versus the lower. This change is mainly due to the disc's cross-sectional area, which is increased in the inferior aspect of the vertebral column.7,16,17 Leatt et al12 and Hirsch11 suggested that the vertebral column may be at risk for injury as a decrease in vertebral flexibility may occur.
No changes in VCH occurred after walking 2 miles, which may suggest a plateau exists in the vertebral column height (VCH) between miles two and three. Two miles may approximate the recommended accumulated 30 minutes of daily activity suggested in the ACSM Guidelines, 1 Surgeon General's Recommendation,3 and Center for Disease Control and Prevention (CDC).2
This study conveys the changes in the VCH to walking over a period of 3 miles. No previous research is available with which to compare these findings. Previous research has been performed on the effects of running on the VCH.9,14 Roush et al14 investigated changes in vertebral column height in male runners over a distance of 3 miles and found a curvilinear relationship between distance and VCH. A decrease in vertebral column height is noted as a result of varying activities and from different loads that are placed upon the body.15 White and Malone15 found that loss of disc height occurs with dynamic activities, such as running, rather than with static loading.Carrigg and Hillemeyer9 reported that static axial pressures are lowest while lying down, higher with standing, and even higher still while sitting and that these static changes occur in a non-linear fashion with most of the compression occurring early in the activity.9 Vertebral column height may decrease with daily activities and even more so with activities that cause an increased axial compressive load throughout the spine.11
With respect to age and sex, evidence from this study has suggested that walking distances of 1-mile or more will have a compressive effect on the VCH in both healthy males and females between the ages of 20 and 40. Ahrens6 showed that significant compression occurred in the spine in both young males ages 20 to 27 and older males ages 50 to 57. It is not evident how height, weight and body mass content, leg length, stride length, shoe type, posture, and length of sleep in a horizontal position the night prior to the study impacted the findings of this study.
The findings from this study suggest that clinicians need to be aware of and consider not only the physiological changes that occur with physical activity, but also our role in the prevention and treatment of such changes. As clinicians, it is important to appreciate the changes that occur in the vertebral column height as a result of repeated compression, such as those that occur with walking, jogging, and running.
The limitations of this study should be noted. Although the sample used to gather results consisted of young healthy adults who had no current complaint of back pain, other age groups with limited walking tolerances due to various medical conditions, specifically low back pain were not included. Given that individuals with chronic low back pain were not measured in this study, it is recommended that a study be performed to investigate the changes in VCH with subjects who have experienced chronic back pain. Another limitation was that the walking pace was uncontrolled, with the exception of participant's maintaining a pace between 12 and 14 on a Borg rating of perceived exertion scale,21 making the effect on the results uncertain. Another major limitation to this study was that the sample consisted of individuals who were all aerobically fit and participating in moderately vigorous exercise three to five times per week. While this sample may not be indicative of the normal population seen in a clinical environment, it does provide a baseline for future studies.
Future research should investigate the changes in VCH when walking on different surfaces, at different inclinations, at varying levels of exercise training, and at differing ratings of perceived exertion. In addition, the impact of limb length, body mass index, height, weight, age, and varying speeds and distances should be investigated.
The purpose of this study was to determine the changes that occur in VCH at every one-half mile, when walking a total distance of 3 miles. The changes were relatively small and much less than reported for running. The loss of VCH was noted within all distance intervals of 1 mile or greater up to 2 miles. These findings support the hypothesis that a change occurs in VCH in healthy males and females over the course of a 3-mile walk.