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Medicine & Science in Sports & Exercise:
doi: 10.1249/MSS.0b013e3181a84db2
APPLIED SCIENCES: Symposium

Effects of Sit-up Training versus Core Stabilization Exercises on Sit-up Performance

CHILDS, JOHN D.1; TEYHEN, DEYDRE S.1; BENEDICT, TIMOTHY M.1; MORRIS, JAMIE B.1; FORTENBERRY, ANDREW D.1; MCQUEEN, RENE M.1; PRESTON, JANICE B.1; WRIGHT, ALISON C.1; DUGAN, JESSICA L.1; GEORGE, STEVEN Z.2

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Author Information

1US Army-Baylor University Doctoral Program in Physical Therapy (MCCS-HMT), Army Medical Department Center and School, Fort Sam Houston, TX; and 2Department of Physical Therapy, Brooks Center for Rehabilitation Studies, University of Florida, Gainesville, FL

Address for correspondence: John D. Childs, P.T., Ph.D., O.C.S., US Army-Baylor University Doctoral Program in Physical Therapy (MCCS-HMT), Army Medical Department Center and School, 3151 Scott Rd, Rm2307, Fort Sam Houston, TX 78234; E-mail: childsjd@gmail.com.

Submitted for publication December 2008.

Accepted for publication March 2009.

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Abstract

Purpose: Core stabilization exercises target abdominal and trunk muscles without the excessive loading that occurs during sit-ups. However, core stabilization exercise programs (CSEP) have not been widely adopted in the US Army partially because of the perceived deleterious impact they would have on performance during the Army Physical Fitness Test. The purpose was to determine whether performing CSEP in lieu of sit-ups during unit physical training would have detrimental effects on sit-up performance and passing rates on the fitness test.

Methods: Soldiers (N = 2616) between 18 and 35 yr of age were randomized to receive a traditional exercise program (TEP) with sit-ups or CSEP. Subjects with a previous history of low back pain or other injury precluding participation in training were excluded. The training programs were completed four times per week for 12 wk. Performance was assessed at baseline and after 12 wk.

Results: Both groups demonstrated significant improvements in sit-up performance and overall fitness scores over time (P < 0.001). There were no significant between-group differences in overall fitness scores (P = 0.142) or sit-up performance (P = 0.543). However, CSEP resulted in a significant improvement in sit-up passing rates by 5.6% compared with 3.9% for the TEP group (P = 0.004).

Conclusions: CSEP did not have a detrimental impact on sit-up performance or overall fitness scores or pass rates. There was a small but significantly greater increase in sit-up pass rate in the CSEP (5.6%) versus the TEP group (3.9%). Incorporating CSEP into Army physical training does not increase the risk of suboptimal performance on the Army's fitness test and may offer a small benefit for improving sit-up performance.

The US Army has incorporated traditional bent-knee sit-ups (with the hands interlocked behind the head) during physical fitness training for many years (2). Sit-ups test muscular endurance for the abdominal and hip flexor muscles and have validated normative standards on the basis of sex and age (2). This exercise has been adopted as part of the military's physical training doctrine on the basis of its ease of testing groups of individuals and on the basis of the notion that lower performance of sit-ups on the Army Physical Fitness Test (APFT) has been associated with a higher incidence of musculoskeletal injuries (13). Sit-ups are also commonly incorporated in general public training routines for the purpose of improving abdominal and hip flexor muscular endurance.

Despite long-standing tradition and widespread popularity of performing sit-ups, it has been postulated that this exercise results in increased lumbar spine loading, potentially increasing the risk of injury and low back pain (LBP). Specifically, sit-ups produce large shear and compressive forces on the intervertebral disc and across the lumbar spine (4,15,18). Increased muscle activation anteriorly during the sit-up results in both an initial hyperextension and a subsequent hyperflexion of the lumbar spine, contributing to high compressive forces of the lumbar spine (19,22).

To address these potential concerns, health and fitness professionals commonly recommend performing alternative "core stabilization" exercises, which are composed of abdominal and trunk muscle strengthening exercises in lieu of sit-ups to improve abdominal muscular fitness (1). These recommendations are based on the accumulated evidence demonstrating that these exercises selectively activate key abdominal and trunk musculature (i.e., transversus abdominis, multifidus, erector spinae, quadratus lumborum, etc.) involved in controlling forces across the lumbar spine (8-12,16). This literature has demonstrated that these exercises should be prescribed on the basis of controlled activation, low load principles that require minimal trunk movements, hence better matching the muscle's function and contributing to improved trunk neuromuscular control (16,23). Advocates of these approaches also point to research indicating that abdominal crunch and trunk stabilization exercises optimize the challenge to the abdominal muscles while minimizing potentially deleterious lumbar spine forces (4,7).

Core stabilization exercises have been supported by the US Army and advocated for inclusion into US Army physical fitness training programs (3); however, US Army personnel are still required to take an APFT that incorporates a 2-min maximal sit-up test. Failure to pass the APFT can have negative consequences on a soldier's career and decrease the chance for promotion; hence, this may be one reason why core stabilization exercise programs (CSEP) have not been widely adopted in the US Army.

Despite the theoretical risk of suboptimal sit-up performance on the physical fitness test, scant empirical evidence is available to inform whether performing a CSEP in lieu of sit-ups is a valid concern. Baxter et al. (5) observed no decrement in sit-up performance among a small cohort of US Military Cadets at West Point who exclusively performed abdominal crunch exercises during a 6-wk training period. However, data demonstrating similar sit-up performance and overall fitness as measured by the APFT among subjects performing a CSEP could inform decision making regarding the development of optimal physical training and fitness assessment programs in the US military. In addition, these data could help inform the design of optimal fitness training programs for the public at large. Therefore, the purpose of this study was to determine whether performing CSEP in lieu of sit-ups during a 12-wk training period has detrimental effects on performance of sit-ups and overall fitness as measured by the APFT. We hypothesized that there would be no differences in APFT sit-up scores or overall passing rates on the basis of whether subjects performed a traditional exercise program (TEP) or CSEP.

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METHODS

Consecutive subjects entering a 16-wk training program at Fort Sam Houston, TX, to become a combat medic in the US Army were considered for participation in this study. This study reports a planned analysis of a proximal outcome of the Prevention of Low Back Pain in the Military clinical trial (NCT00373009) (6), which has been registered at http://clinicaltrials.gov.

In the primary trial, subjects were randomized in clusters to receive CSEP alone, CSEP with a psychosocial education program, TEP, or TEP with a psychosocial education program. Subjects are currently being followed monthly for 2 yr after completion of training to assess the long-term outcomes of LBP occurrence and severity. However, the primary trial results are not yet available. Because the educational program was not designed to impact sit-up performance, we collapsed the study into two groups (TEP or CSEP) for the purpose of this analysis.

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Subjects.

Research staff at Fort Sam Houston, TX, introduced the study to individual companies of soldiers and obtained written informed consent. For eight consecutive months, subjects were screened for eligibility according to the inclusion/exclusion criteria. Subjects were required to be 18-35 yr of age (or 17-yr-old emancipated minor), participating in training to become a combat medic, and be able to speak and read English. Subjects with a prior history of LBP were excluded. A prior history of LBP was operationally defined as LBP that limited work or physical activity, lasted longer than 48 h, and caused the subject to seek health care. Subjects were also excluded if they were currently seeking medical care for LBP; were unable to participate in unit exercise owing to injury in foot, ankle, knee, hip, neck, shoulder, elbow, wrist, or hand; had a history of fracture (stress or traumatic) in proximal femur, hip, or pelvis; were pregnant; or had transferred from another training group. Other possible exclusions included soldiers who were being accelerated into a company already randomized and recruited for participation in the Prevention of Low Back Pain in the Military trial or soldiers who were being reassigned to an occupational specialty other than a combat medic.

Refer to Figure 1 for a flow diagram describing the number of patients considered for this trial, eventually enrolled into the trial, and completed follow-up assessment, as per the Consolidated Standards of Reporting Trials guidelines (17). The institutional review boards at the Brooke Army Medical Center (San Antonio, TX) and the University of Florida (Gainesville, FL) granted approval for this project. All subjects provided written informed consent before their participation.

FIGURE 1-Flow diagra...
FIGURE 1-Flow diagra...
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Randomization.

Military training environments require living in close quarters with other members of the unit, making individual randomization an unfeasible option for this trial because of concerns related to disruption of normal training schedule and treatment contamination. Therefore, a cluster randomization strategy was used for assigning companies to receive TEP or CSEP. This meant that for a given company, every subject who consented to the study received the same study condition. Cluster randomization is a viable methodological choice that has been effectively used in other large samples of primary prevention (20,21,24). The randomization schedule was prepared by computer and was determined before recruitment began. The randomization schedule was balanced to ensure equal allocation to each condition after 12 companies were recruited.

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Exercise programs.

Subjects in both groups performed the assigned exercise program in a group setting under the direct supervision of their drill instructors as part of daily unit physical training. The exercise regimen in both groups consisted of five to six exercises, each of which was performed for 1 min. Exercise programs were performed daily, for a total dosage time of approximately 5 min·d−1, 4 d·wk−1 during a period of 12 wk. Performing the exercise programs under the supervision of a drill instructor and in a group setting helped to ensure compliance with the assigned program and dosage. Additional details regarding each exercise program is included in Table 1 and in the Appendix.

Table 1
Table 1
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The subjects' drill instructors received comprehensive training in the study procedures by the staff before the study's initiation. Drill instructors were provided detailed training cards specific to each program. This information was also provided to the drill instructors on the study's Web site (http://polm.ufl.edu) for reference purposes. This training ensured that both the drill instructors and the subjects were proficient in their assigned exercise programs and enhanced the ability to accomplish the exercise programs in a standardized manner. Study personnel monitored physical training for an average of 2 d·wk−1 during the 12-wk training period to answer questions and to monitor compliance with the assigned exercise program.

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Measurements.

Study-related measures were collected by research personnel unaware of randomization assignment before training and 12 wk later when training was completed. All measures were scored in a masked manner by a computer algorithm. Subjects provided standard demographic information such as age, sex, past medical history, etc., and completed a variety of health outcome measures. It was not possible to blind subjects to group assignment because they actively participated in their randomly assigned training program. However, APFT fitness scores were collected by drill instructors according to standard testing procedures outlined later (2). The drill instructors were not formally involved with the study other than within the context of the usual training environment.

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APFT procedures.

Subjects' physical fitness was assessed at baseline and after their randomly assigned 12-wk training program according to established Army standards for conducting the APFT (2). The APFT consists of three events: 1) maximum sit-up performance in 2 min, 2) maximum push-up performance in 2 min, and 3) a timed 2-mile run. Scores for each event are based on age- and sex-stratified normative data and ranged from 0 to 100 points for each event. A soldier must score at least 60 points in each of the three events to pass, thus a minimum passing score of 180 points. Failure to achieve at least 60 points in any single event, regardless of performance in the other two events, results in an overall failure.

The sit-up event of the APFT begins with the command "get set." Subjects lie on their backs with the knees bent at a 90° angle and the feet together or up to 12 inches apart. Another person holds the ankles. Other methods of bracing or holding the feet are not permitted. The heel is the only part of the foot that must stay in contact with the ground. The subjects' fingers must be interlocked behind the head, and the backs of the hands are required to touch the ground. The exercise commences when the subject begins raising the upper body to, or beyond, the vertical position. The vertical position is defined as the base of the subject's neck being above the base of the spine. After the subject has reached or surpassed the vertical position, the subject lowers his body until the bottom of his shoulder blades touch the ground. The subject's head, hands, arms, or elbows do not have to touch the ground. A repetition is not counted if the subject fails to reach the vertical position, fails to keep his fingers interlocked behind his head, arches or bows his back, raises his buttocks off the ground to raise his upper body, or lets his knees exceed a 90° angle. If the standard is not met, the repetition does not count and the scorer repeats the number of the subject's last correctly performed sit-up to let the subject know a violation occurred. The up position is the only authorized rest position. If the subject stops and rests in the down (starting) position, the event will be terminated. As long as the subject makes a continuous physical effort to sit-up, the event will not be terminated. The subject may not use his hands or any other means to pull or push himself to attain the up (resting) position or to hold himself in the rest position. If the subject does this, his performance will be terminated. The subject has 2 min to perform as many sit-ups as possible. The total number of sit-ups performed in 2 min is adjusted on the basis of sex and age according to established Army standards (2). Similar standards exist for the performance of the push-up and 2-mile run events.

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Data analysis.

Descriptive statistics, including measures of central tendency and dispersion for continuous variables, were calculated to summarize the data. Demographic and baseline levels of variables were compared between the two randomly assigned groups using t-test for comparison of means and χ2 tests for comparison of proportions.

Independent variables were group with two levels (TEP and CSEP), quartile with four levels (0%-25%, 26%-50%, 51%-75%, and 76%-100%), and time with two levels (baseline and 12 wk). Quartile was considered to determine whether there were differential effects on sit-up up performance at the extremes of the range of performance. Dependent measures were scores and pass rates for the sit-up event and overall APFT.

A 2 × 4 × 2 (group × quartile × time) repeated-measures ANOVA with pairwise comparisons using the Bonferroni inequality was performed to examine differences in the overall fitness and sit-up performance scores. Differences in pass rates were assessed with a χ2. The α level was set to 0.05 a priori. Subjects with missing data were excluded because the purpose of this study was to determine the impact of performing CSEP in lieu of sit-ups on the basis of the condition that subjects actually completed the full training period.

The number needed to treat (NNT) is an epidemiological measure used in assessing the effectiveness of health-care interventions and conceptually represents the number of patients who need to be treated to prevent one additional bad outcome, thus lower NNT values imply fewer patients need to be treated to observe the benefit (14). We calculated the NNT statistic in this study to determine the relative impact of performing CSEP versus TEP to improve passing rates on the sit-up event of the APFT. In this instance, the "treatment" is the randomly assigned exercise training program (TEP or CSEP) and the "bad outcome" is a failure on the sit-up event of the APFT. All statistical analyses were performed using SPSS 12.0 (SPSS, Inc., Chicago, IL).

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RESULTS

A total of 3916 subjects were screened for inclusion into the study. There were 1061 (27%) who were ineligible and therefore excluded from further consideration, leaving 2855 eligible subjects. The reasons for ineligibility included being outside the age range; having a history of LBP; currently seeking care for LBP; prior surgery for LBP; currently not performing physical training; having a history of fracture of the proximal femur, pelvis, or hip; being pregnant; or being transferred in from another company. Among those eligible, 2033 subjects (71%) consented to participate (Fig. 1). There were 235 (11.6%) subjects for whom at least one event of the baseline APFT fitness score was missing because of a current injury that prevented them from completing the sit-up, the push-up, or the 2-mile run event, thus their data were excluded for the purposes of this proximal analysis. Of the remaining 1798 subjects, 331 (18.4%) did not have complete data for the 12-wk APFT fitness score, thus a total of 1467 subjects (81.6%; TEP: n = 706, TEP and CSEP: n = 761) were included in the completers-only analysis (Fig. 1).

The mean age of subjects was 21.9 ± 4.3 yr (73.3% male; Table 2). Descriptive statistics for each group categorized by quartile are included in Table 3. There was no significant group × time × quartile interaction for performance on either overall fitness (P = 0.164) or sit-up scores (P = 0.543) on the APFT (Table 3). Both groups demonstrated significant improvements in their sit-up scores (P < 0.001; Table 3) and overall fitness scores over time (P < 0.001; Table 4). Subjects in the top quartile for both groups demonstrated a small but significant decrease in sit-up performance from baseline to 12 wk (P < 0.001), indicating the potential for a ceiling effect to have occurred. Both groups performed sit-ups outside the unit physical training at equal rates overall (TEP = 69.5% and CSEP = 65%; P = 0.067) and equal frequencies on the basis of days per week (<3, 3-5, and >5 d; P = 0.320). Table 5 also displays the frequencies with which subjects in each group performed sit-ups outside the unit physical training on the basis of the baseline sit-up score quartile. Regardless of the baseline sit-up quartile, there were no significant differences in the percentage of subjects who performed sit-ups outside the unit physical training (Table 5).

Table 2
Table 2
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Table 3
Table 3
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Table 4
Table 4
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Table 5
Table 5
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There was also no significant group × time interaction for either the score of the overall APFT fitness (P = 0.142; Table 4) or the score on the sit-up component of the APFT (P = 0.543; Table 3) after 12 wk of training; however, CSEP resulted in a significant improvement in sit-up passing rates by 5.6% compared with 3.9% for the TEP group (P = 0.004; Table 6). The corresponding NNT for CSEP to improve passing rates on the sit-up event of the APFT was 56.

Table 6
Table 6
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DISCUSSION

The results of this study suggest that performing core stabilization exercises in lieu of traditional sit-ups during unit physical training did not have a deleterious impact on either performance or passing rates for sit-up or overall fitness as assessed with the APFT. Both groups significantly improved their overall fitness and sit-up performance on the APFT at a similar rate between the baseline and the 12-wk follow-up, suggesting that the omission of sit-ups during unit physical training in favor of a CSEP does not lead to decrements in performance on the APFT. In fact, there was a small but significantly greater increase in sit-up passing rates with CSEP (5.6%) versus TEP (3.9%).

The baseline to 12-wk change data in Table 6 represent a small but significantly greater increase in sit-up pass rate in the CSEP (5.6%) versus the TEP group (3.9%). Therefore, to help interpret the meaningfulness of this finding, we calculated the NNT for CSEP to improve passing rates on the sit-up event of the APFT, which was 56. In other words, in a company of 400 soldiers, approximately 34 soldiers will fail the sit-up event of the APFT. After 12 wk of TEP, 15 of those 34 soldiers would improve from a failing to a passing score on the sit-up event. Conversely, 22 of 34 subjects in the CSEP group would progress from a failing score to a passing score, indicating that performing CSEP resulted in a net seven additional subjects progressing from a failing to a passing score on the sit-up event of the APFT compared with TEP. It is possible that the significant improvement in passing rates observed in favor of the CSEP group (Table 6) may represent a type I error due to the large sample size, thus bringing into question the meaningfulness of this finding. Nevertheless, these data may be important to consider in future research and to inform policy decision making regarding the potentially protective role of CSEP on sit-up performance.

The results of this study differ in several ways from the findings of Baxter et al. (5). For example, our population consisted of enlisted soldiers in the military with an average baseline sit-up score of 77%. This is a more representative population of the Army as a whole compared with Baxter who included officer candidate cadets at US Military Academy at West Point, with an average baseline sit-up score of 95% (5). Furthermore, the composition of the exercise programs and dosing of the intervention was different. The training program in the Baxter study was limited to performing abdominal crunches for 6 wk (5), whereas the subjects in our study performed 12 wk of a CSEP composed of abdominal crunches among a more comprehensive trunk strengthening program. Despite these differences, both studies found no decrease in sit-up performance when traditional sit-ups were omitted from a physical training program for a maximum of 12 wk (5).

One of the potential confounding factors anticipated before the study was that subjects in the CSEP group might not be compliant with the instructions to avoid performing sit-ups outside the unit physical training because of perceived deleterious impact that not performing sit-ups might have on their APFT fitness scores. It was unrealistic to precisely control for sit-up exposure outside the unit physical training because graduation from training and opportunity for promotion are dependent on passing the fitness test; therefore, we assessed compliance with the assigned training program as part of the 12-wk follow-up by assessing the extent to which subjects in each group performed sit-ups outside the unit physical training. Subjects in both groups performed sit-ups outside the unit physical training at equal rates (TEP = 69.5% and CSEP = 65%; P = 0.067); therefore, only 35% of subjects in the CSEP group did not perform sit-ups outside the unit physical training. However, there was no difference between the groups in the frequency with which subjects performed sit-ups outside the unit physical training (<3, 3-5, and >5 d). It may be that the frequency of performing sit-ups outside the unit physical training may simply be an indicator of the normal amount of training that routinely occurs outside the more formal unit physical training.

We further analyzed the frequency of performing sit-ups outside the unit physical training on the basis of the baseline sit-up quartile if subjects more at risk for suboptimal performance on the APFT (0-50th percentile) and who were assigned to the CSEP might be more inclined to perform sit-ups outside the unit physical training compared with subjects in the TEP group in the same quartile. However, there were no significant differences in the frequency of performing sit-ups outside the unit physical training between the groups regardless of quartile. Although there were trends for differences between the groups in the 100th percentile (P = 0.05; Table 5), the difference was in favor of the TEP; thus, this finding does not support the argument that performing sit-ups outside the unit physical training in the CSEP confounded the results.

It might also be expected that subjects in the CSEP group who performed additional sit-ups would demonstrate improved sit-up performance and passing rates on the APFT compared with subjects who did not, again confounding the study's interpretation. However, a sensitivity analysis revealed no difference in sit-up performance and overall passing rates on the APFT between subjects in the CSEP group who performed sit-ups outside the unit physical training and those who did not. This finding lends further evidence to suggest that the performance of additional sit-ups outside the unit physical training did not confound the results and reinforces the notion that soldiers, commanders, and health policy decision makers should not be concerned that performing CSEP in lieu of sit-ups will lead to decreased performance on the APFT. It should be noted that because both groups performed sit-ups outside the unit physical training at equal rates, the results of the study may be attributable to CSEP plus sit-up training outside the unit physical training compared with TEP plus sit-up training outside the unit physical training.

Another potential concern was that subjects in the CSEP group who were on the margin of failing the sit-up event on the APFT at baseline (0-50th percentile) might be more adversely impacted by CSEP than subjects with preexisting performance levels above the passing thresholds (51st to 100th percentile) because even small decrements or failure to improve sit-up performance among subjects in the lower quartiles could pose an increased risk of not passing the sit-up event. Conversely, it would take a large negative change in sit-up performance to impact passing rates among subjects in the top quartiles, even if CSEP was found to be associated with decreased sit-up performance. In other words, it is logical to presume that subjects in the top two quartiles would likely pass the sit-up event on the APFT regardless of group assignment. However, it turned out that there was no significant quartile effect overall, meaning that within each quartile, subjects improved their scores at a similar rate, regardless of whether they completed TEP or CSEP.

Subjects in the top quartile for both groups demonstrated a small but significant decrease in sit-up performance during the 12-wk period. Given preexisting high levels of fitness, the potential to demonstrate improvements was minimal, thus indicating the potential for a ceiling effect to have occurred. However, the magnitude of this decrease (3.4 and 2.5 points for the CSEP and TEP groups, respectively) had no material impact on passing rates because these subjects' fitness level was already in the top quartile. Therefore, the results of this study may not be generalizable to subjects with exceptionally high levels of physical fitness. Further research could be conducted on elite athletes or other populations of soldiers with high levels of physical fitness using an extended scoring scale that could detect higher levels of physical fitness and incorporated factors related to the influence of motivation on fitness test performance.

Despite evidence from the biomechanical literature supporting the benefits of abdominal crunch and core stabilization exercises and data from this trial suggesting that performing these exercises does not have a deleterious impact on overall fitness or maximal performance of sit-up as assessed on the basis of the APFT, little information is available suggesting whether the increased loads encountered with traditional sit-ups actually contribute to increased injury rates. If this is the case, these data would discredit the validity of including sit-ups as a component of the unit physical training or assessing sit-up performance in the APFT. We can confidently conclude that future research can examine whether CSEP offers protection against the development of musculoskeletal injuries such as LBP without having to be unduly concerned that doing so will lead to substantial increases in failure rates on the APFT. The results of follow-up studies will assist policy makers in constructing the physical fitness training programs and fitness assessment methodologies that offer the most protection against developing musculoskeletal injuries and maintain optimal physical fitness.

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CONCLUSIONS

Performing core stabilization exercise does not increase the risk of suboptimal performance of sit-ups or overall fitness as assessed with the APFT. Therefore, CSEP can be incorporated into physical fitness programs without concern that doing so will have a deleterious impact on sit-up performance or overall fitness scores. In fact, of a typical company of 400 soldiers, CSEP could result in 7 additional soldiers progressing from failing to passing the sit-up event compared with TEP, demonstrating the potential for core stabilization exercises to improve performance of sit-ups in those with the lowest fitness scores. Although the magnitude of this benefit on the APFT may be considered small and future research is needed to determine the extent to which an improvement in passing rates on the sit-up event with CSEP would be realized, we can confidently conclude that performing CSEP in lieu of traditional sit-ups during unit physical training does not result in a decrement in the overall fitness or sit-up performance and passing rates on the APFT. In light of these data that CSEP can be studied without concern for increasing failure rates on the APFT, combined with a potentially important benefit of actually improving APFT fitness scores, future research from the primary study will determine whether CSEP is protective against the development of musculoskeletal injuries such as LBP. These data can also be used to inform health policy decision making because it relates to designing optimal health and fitness training and assessment programs for both military and civilian populations.

Congressionally Directed Peer Reviewed Medical Research Program (No. W81XWH-06-1-0564). The Prevention of Low Back Pain in the Military trial is supported by the peer-review medical research program of the Department of Defense (PR054098).

The authors thank Christopher Barnes, Yang Li, and Erik Henrickson for the creation and management of the Web site and database and Donna Cunningham for her administrative assistance.

The results of the present study do not constitute endorsement by the American College of Sports Medicine.

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APPENDIX
TEP
The sit-up

The sit-up was to be performed as the first and last exercise in the set of five exercises.

Starting position (Fig. A1): On the command, "Start position, move," the subject was supine in standard sit-up position, knees bent at 90°, with hands interlocked behind the head.

FIGURE A1-Start and ...
FIGURE A1-Start and ...
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Exercise instructions (Fig. A2): On the command, "Exercise position, move," the subject was to bend and lift the upper body until shoulders and hips were parallel. Then the subject was to return to the starting position. The subject was to perform as many repetitions as possible in 1 min.

FIGURE A2-Exercise p...
FIGURE A2-Exercise p...
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The sit-up with trunk rotation

Starting position (Fig. A1): On the command, "Start position, move," the subject was supine in standard sit-up position, knees bent at 90°, with hands interlocked behind the head.

Exercise instructions (Fig. A3): On the command, "Exercise position, move," the subject was to lift, bend, and rotate the upper body to the left until the right elbow touches the outside portion of the left knee. Then the subject was to return to the starting position. The subject was to perform as many repetitions as possible in 1 min to the left side and then repeat above to the right side for as many repetitions as possible in 1 min.

FIGURE A3-Exercise p...
FIGURE A3-Exercise p...
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The abdominal crunch

Starting position (Fig. A1): On the command, "Start position, move," the subject was supine in standard sit-up position, knees bent at 90°, with hands interlocked behind the head.

Exercise instructions (Fig. A4): On the command, "Exercise position, move," the subject was to lift the upper body from the ground until the bottom borders of the shoulder blades cleared the ground and then quickly return to the start position. The subject was to perform as many repetitions as possible in 1 min.

FIGURE A4-Exercise p...
FIGURE A4-Exercise p...
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CSEP
The abdominal drawing-in crunch maneuver

Starting position (Fig. A1): On the command, "Start position, move," the subject was supine in standard sit-up position, knees bent at 90°, with hands interlocked behind the head.

Exercise instructions (Fig. A5): On the command, "Exercise position, move," the subject was to draw abdominal muscles up and in toward the spine, then lift the upper body from the ground until the bottom borders of the shoulder blades clear the ground. This position was to be held for 10 s. Six repetitions of this exercise were to be performed in 1 min.

FIGURE A5-Exercise p...
FIGURE A5-Exercise p...
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The horizontal side support

Starting position (Fig. A6): On the command, "Start position, move," the subject was to lie on the right side with knees straight, left leg resting in front of the right leg and upper body supported with the right elbow, with the left hand supporting the right shoulder.

FIGURE A6-Start and ...
FIGURE A6-Start and ...
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Exercise instructions (Fig. A7): On the command, "Exercise position, move," the subject was to draw in the abdominal muscles, and for a count of 5, lift the body from the ground with the body weight supported by the arms and feet. This position was to be held for 5 s. Then the body was to lower to the ground during a count of 5. The subject was to perform six repetitions of this exercise on the right side for 1 min and then repeat six repetitions of this exercise on the left side for 1 min.

FIGURE A7-Exercise p...
FIGURE A7-Exercise p...
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The supine shoulder bridge

Starting position (Fig. A8): On the command, "Start position, move," the subject was supine in standard sit-up position, knees bent at 90°, with hands interlocked behind the head and instructed to pull in the abdominal muscles as in the abdominal drawing-in crunch maneuver.

FIGURE A8-Start and ...
FIGURE A8-Start and ...
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Exercise instructions (Fig. A9): On the command, "Exercise position, move," for a count of 5 s, the subject was to raise the hips and lower back off the ground until the body from the trunk to knees was in a straight line, with weight evenly distributed on the shoulders and feet. With the buttocks still raised, one leg was to be straightened out until it was in line with the trunk and thigh. This elevated position was to be held for 5 s in the elevated position and then lowered to the ground during a count of 5. With each repetition, the subject was to alternate each leg that was extended. The subject was to perform four repetitions of this exercise in 1 min.

FIGURE A9-Exercise p...
FIGURE A9-Exercise p...
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The quadruped alternating arm and leg

Starting position (Fig. A10): On the command, "Start position, move," the subject was to assume the quadruped position on the hands and knees and instructed to pull in the abdominal muscles as in the abdominal drawing-in crunch maneuver.

FIGURE A10-Start and...
FIGURE A10-Start and...
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Exercise instructions (Fig. A11): On the command, "Exercise position, move," for a count of 5 s, the subject alternately extended one leg and the opposite arm. This position was held for 5 s. Then both extremities were lowered to the ground during a count of 5. This movement was repeated with the opposite arm and leg. The subject was to perform four repetitions in 1 min.

FIGURE A11-Exercise ...
FIGURE A11-Exercise ...
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The woodchopper

Starting position (Fig. A12): On the command, "Start position, move," the subject was to assume a straddle stance with the arms overhead, hands joined, and fingers interlaced. They were further instructed to make sure to have the hips set, abdominals tightened, and arms extended as fully overhead as possible.

FIGURE A12-Start and...
FIGURE A12-Start and...
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Exercise instructions: Count 1 (Fig. A13)-On the command, "Exercise position, move," the subject was to begin squatting with the heels flat while lowering the arms between the knees. The shoulders, knees, and balls of the feet should be aligned and the trunk should remain straight and tilted forward with the heels remaining on the ground. Count 2 (Fig. A14)-The subject was to move through the starting position to rise onto the balls of the feet, making sure not to let the trunk arch backward. Count 3 (Fig. A13)-The subject was to begin squatting with the heels flat while lowering the arms between the knees. The shoulders, knees, and balls of the feet should be aligned. The trunk should remain straight and tilted forward with the heels remaining on the ground. Count 4 (Fig. A14)-The subject was to move through the starting position to rise onto the balls of the feet, making sure not to let the trunk arch backward. Completion of counts 1-4 of the exercise sequence at a moderate pace constituted completion of one repetition of this exercise. This exercise was to be performed rhythmically for 1 min. After the last repetition, the subject was to halt at the starting position.

FIGURE A13-Exercise ...
FIGURE A13-Exercise ...
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FIGURE A14-Exercise ...
FIGURE A14-Exercise ...
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Keywords:

FITNESS; LOW BACK PAIN; LUMBAR SPINE; PREVENTION; MILITARY

©2009The American College of Sports Medicine

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