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The Effectiveness of Traditional and Sling Exercise Strength Training in Women

Dannelly, Bethany D; Otey, Sarah C; Croy, Ted; Harrison, Blain; Rynders, Corey A; Hertel, Jay N; Weltman, Arthur

Journal of Strength and Conditioning Research: February 2011 - Volume 25 - Issue 2 - p 464-471
doi: 10.1519/JSC.0b013e318202e473
Original Research
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Dannelly, BD, Otey, SC, Croy, T, Harrison, B, Rynders, CA, Hertel, JN and Weltman, A. The effectiveness of traditional and sling exercise strength training in women. J Strength Cond Res 25(2): 464-471, 2011-Strength training often combines closed-kinetic-chain exercises (CKCEs) and open kinetic-chain exercises (OKCEs). The CKCE may be more effective for improving performance in lower-body training. Recently, we reported upper-body CKCE (using a commercially available system of ropes and slings, Redcord AS, Staubo, Norway) was as effective as OKCE training for strength gains and that CKCE was more effective than OKCE for improving throwing performance. To our knowledge the effectiveness of a strength training program that uses exclusively CKCE is unknown. In this study, we examined the effectiveness of CKCE vs. OKCE strength training programs in women enrolled in an introductory strength training program. Twenty-six participants were randomized to OKCE (traditional exercises) or CKCE (sling-based exercises). Participants completed 6 sets per week for 13 weeks. Pre and posttraining evaluations included the following: 1 repetition maximum (1RM) leg and bench press; sling exercise push-ups; isokinetic dynamometry; lateral step-down test; and the Star Excursion Balance Test. Both groups significantly improved bench press (by an average of 4-6 kg) and leg press (by an average of 23-35 kg) (p < 0.001). There was a significant group × time interaction (p < 0.001) for sling exercise push-ups (OKCE pre = 5.5 ± 8.6, OKCE post = 6.1 ± 8.2, CKCE pre = 6.8 ± 6.0, CKCE post = 16.9 ± 6.6). Isokinetic measures of knee extension, knee flexion, shoulder internal rotation, and shoulder external rotation increased (improvements ranged from 2.7 to 27.7%), with no group differences. Both OKCE and CKCE strength training elicited similar changes in balance. We conclude that CKCE training is equally as effective as OKCE training during the initial phases of a strength training program in women. The fact that only CKCE improved sling exercise push-ups supports previous findings suggesting functional superiority of CKCE.

Department of Human Services, Curry School of Education, University of Virginia, Charlottesville, Virginia

Address correspondence to Arthur Weltman, Alw2v@virginia.edu.

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Introduction

Strength training programs typically combine closed- and open-kinetic-chain exercises to improve overall strength. Open-kinetic-chain exercises (OKCEs) are performed with the terminal segment, typically the hand or foot, free to move with the load applied to the distal portion of the limb such as in the bench press or leg extension exercise. These exercises are usually non-weight bearing, with the movement occurring at the elbow or knee joint (6,13). Closed-kinetic-chain exercises (CKCEs) are exercises performed where the hand (for arm movement) or foot (for leg movement) is fixed and cannot move, such as a squat or push-up. The hand or foot remains in constant contact with the surface, usually the ground or the base of a machine. These exercises are typically weight-bearing exercises, where exercisers use their own body weight with or without external weight. The CKCEs tend to work more than 1 muscle group and joint simultaneously (6,13).

Several studies have shown that CKCEs may be more effective than OKCEs in improving performance-related measures in lower-body training (1,3). For example, lower-body CKCE training is more effective than OKCE training for improving vertical jump performance (1,3,13). Further, CKCEs are commonly prescribed for athletes, possibly because they result in less anterior and posterior tibiofemoral shear force than lower-body OKCEs do (6,10,16). Studies also have shown that lower-body CKCE generate muscular co-contraction, which provides greater joint stability than OKCE (7,16).

Studies conducted on upper-body strength training have shown that CKCEs are typically limited by body weight as a source of resistance so low repetition, high-intensity strength training can be difficult to execute (4,11). Thus, OKCEs are commonly employed in upper-body strength programs. Despite these perceived limitations, it has been shown that CKCEs can be effective for upper-body training (4,11). Similar to the lower-body exercises, upper-body CKCEs elicit muscular co-contractions, thus providing dynamic joint stability, which does not occur with OKCEs (11,13). A recent study from our laboratory found that substituting 4 upper-body CKCEs was as effective as OKCE training in producing maximal strength gains in collegiate softball players (13); however, only CKCE training significantly improved throwing velocity. Based on these findings, it is reasonable to conclude that CKCE training can be incorporated into upper-body strength training without sacrificing gains in maximal strength or performance criteria. Although some studies have shown that CKCE training may be as or more effective than OKCE training, to our knowledge, no data exist on the effectiveness of a strength training program that uses CKCEs exclusively (1,3,6,7,10,11,13,16). The use of CKCE may have particular utility for individuals who may be intimidated by traditional weight training settings.

For example, women beginning a weight training program are often uncomfortable in a typical weight room setting and as such may choose not to engage in this important activity (8). In this study, we compared a sling-based CKCE training program to an OKCE training program in a group of women enrolled in an introductory strength training program. We hypothesized that after training, both CKCE training and OKCE training would increase 1 repetition maximum (1RM) bench and leg press, and Biodex peak torque (PT) and power to a similar degree. We also hypothesized that performance on CKCE and dynamic balance would improve more with CKCE training because of specificity of training and the extra demands CKCE place on core stability.

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Methods

Experimental Approach to the Problem

This study included 1 independent variable with 2 levels (pre- and post-13 weeks of strength training) and 13 dependent variables. The independent variable was the type of training in which the subject engaged (CKCE or OKCE). Dependent variables included isokinetic concentric phase PT for knee flexion and extension and for shoulder internal and external rotation; isokinetic concentric phase peak power (PP) for knee flexion and extension and for shoulder internal and external rotation; 1RM bench press and 1RM leg press; lateral step-down test; Star Excursion Balance Test (SEBT); and maximum sling exercise push-ups.

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Subjects

The study was approved by the university's institutional review board. Twenty-nine female undergraduate students at the University of Virginia were recruited from Lifetime Physical Activity weight training classes (mean age = 19.6 ± 1.11 years, mean weight = 60.5 ± 7.2 kg, mean height = 166.4 ± 5.9 cm). All participants were enrolled in an introductory strength training class and provided written informed consent. Participants had 1 week (2 or 3 sessions) to learn basic weight training techniques and safety guidelines. Three subjects withdrew from the study. Two subjects dropped the course, and 1 subject was unable to complete the study because of work-related conflicts. Three additional subjects were unable to complete all aspects of performance testing because of pre-existing orthopedic injuries, but measures they were able to complete are included (resulting in n = 23 to n = 26, depending on the variable tested).

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Procedures

Performance Testing

Pre and posttraining testing consisted of isokinetic concentric phase PT for knee flexion and extension and for shoulder internal and external rotation; isokinetic concentric phase PP for knee flexion and extension and for shoulder internal and external rotation; 1RM bench press and 1RM leg press; lateral step-down test; SEBT; and maximum sling exercise push-ups.

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Isokinetic Strength Testing

Isokinetic strength testing was performed using a Biodex System 3 multijoint dynamometer (Shirley, NY, USA). All subjects performed 3 sets of 5 trials of each exercise with 90 seconds between sets. Verbal encouragement was given for each repetition and testing was preceded with 10-15 practice repetitions to familiarize the subject with the isokinetic device. Concentric internal rotation and external rotation tests intraclass correlation coefficients [ICCs] = 0.81 and 0.74 for internal and external rotation, respectively) were conducted at 180° s−1 through a 65° arc of motion, with the seatback angle set at 85°. The tested extremity was abducted approximately 25°, and shoulder flexed slightly to place the shoulder in the scapular plane for testing. Dynamometer and seat height were adjusted such that the humerus was in line with the rotor, as recommended by the manufacturer. The isokinetic knee flexion and extension test (ICCs = 0.91 and 0.92 for flexion and extension, respectively) was also performed at 180° s−1 from full knee extension (0°) to approximately 85-90° of flexion for 3 sets of 5 test repetitions with a 90-second rest period between sets. The seatback angle was set at 85°, and the hips were in 90° of flexion. Values from the 3 sets were averaged to find PT and power values for each subject.

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1RM Testing

The 1RM testing was performed using the National Strength and Conditioning Association 1RM protocol (2). Participants began the 1RM bench press and leg press assessments by warming up with repetitions on the bench press on 45-lb bars and free weights (York Barbell, York, PA, USA) and repetitions on the leg press machine (Hammer Strength, Schiller Park, IL, USA). The goal was to build to the 1RM load by approximately the fifth set. For the bench press, a successful repetition was scored if the weight was lowered to the chest and raised to full arm extension without subject losing foot, hip, back, or shoulder contact with the bench or the floor, and no help was provided by the spotter. For the leg press, a successful repetition was scored if the weight was lowered such that the knees created a 90° angle and raised to full leg extension without the subject losing back or shoulder contact with the machine and without help from the spotter. Three failed repetitions at a given weight or voluntary termination ended each test.

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Lateral Step-Down Test

The quality of movement during the lateral step-down test was assessed by a trained investigator using a scale designed for this purpose. Each participant was asked to stand on single-leg support with hands on the waist, knee straight, and weight-bearing foot on the edge of a 20-cm-high step. The contralateral leg was held, fully extended, over the floor adjacent to the step. The participant was then asked to bend the tested knee until the contralateral leg lightly touched the floor and then re-extend the knee to the start position. This was repeated for 3 repetitions. The investigator faced the subject and scored the test based on 5 criteria, described in detail elsewhere (12): (a) Arm strategy, (b) Trunk movement, (c) Pelvis plane, (d) Knee position, and (e) Maintenance of steady unilateral stance. A point was added for an unsuccessful execution of each of the 5 criteria during any of the 3 repetitions. Each subject received a score between 0 and 6.

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Star Excursion Balance Test

The anterior, posteromedial, and posterolateral components of the SEBT were conducted by a trained investigator using a “Y” that was taped the floor (ICCs range from 0.85 to 0.96 depending on movement). Participants were asked to stand on 1 leg with their toe at the base of the upper part of the “Y.” While maintaining this single-leg stance, the participant was asked to reach with the free leg in the specified direction (5,9). Reach was measured in centimeters, and each participant completed 3 trials. Measurements from the 3 trials were averaged and normalized to subject leg length. Reach was also measured on the opposite foot in all 3 planes of movement.

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Sling Exercise Push-Ups

Sling exercise push-ups were performed with a Redcord minitrainer (Kilsund, Norway). Handles were approximately 10 cm above the ground with participants positioned on their knees. An investigator instructed each participant in proper push-up form and counted the number of successful repetitions. A repetition was considered successful if the subject lowered her chest to the height of her hands while maintaining core stability and posture. Failure to maintain proper form or failure to continuously progress from 1 repetition to the next terminated the test.

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Training Intervention

Participants were randomized to 1 of 2 training intervention groups: OKCE training and CKCE training. Participants completed 6 sets of strength training exercises per week for 13 weeks. Based on course enrollment and time, some participants completed 3 sessions per week, performing 2 sets during each session, whereas others completed 2 sessions per week, performing 3 sets during each session. Investigators supervised all exercise sessions. The duration, relative intensity, and volume of each set were the same for both treatment groups. All participants were instructed to refrain from strength training outside of treatment sessions.

The CKCE group completed a full-body strength training program with Redcord minitrainers hung from ceiling beams, which consists of ropes with slings and handles that can be adjusted. Exercise intensity was controlled by adjusting handle height relative to the floor, foot height, and leg and hand position relative to the rope fulcrum. Although there was some trial and error in the determination of relative intensity of major pull and press lifts, all subjects realized their full capabilities within the first full week of training. By keeping the handles elevated, subjects could complete exercises with intensity and volume comparable with those in the OKCE group.

The OKCE group trained with free weights, dumbbells (York Barbell, York, PA, USA), and machines (Hammer Strength, Schiller Park, IL, USA). Exercise intensity and volume were adjusted relative to a subject's 1RM for major press and pull lifts. Intensity for exercises was determined by subject familiarity and proper form.

Examples of commonly selected OKCE and their CKCE analogs, in italics, are shown: (a) Barbell flat bench press/bilateral push-ups, (b) Cable seated row/bilateral inverted row, (c) Dumbbell biceps curl/biceps curl, (d) Triceps pulldown/triceps extension, (e) Shoulder extension/shoulder extension, (f) Pullover/Pullover, (g) Hip abduction/hip abduction, (h) Hip adduction/hip adduction, (i) Leg extension/leg extension-prone bridge, and (j) Leg curl/leg curl-supine bridge-leg press.

Figure 1 provides visual examples of OKCE-CKCE exercise pairs.

Figure 1

Figure 1

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Statistical Analyses

Statistical calculations were performed using Statview version 5.0.1 (SAS Institute, Cary, NC, USA). A 2-factor analysis of variance (ANOVA) with repeated measures was executed with the treatment group (CKCE or OKCE) as the independent variable. The dependent variables were the outcome measures for the various performance tests. Thus, there was 1 between-subjects factor (training group) and 1 within-subjects factor (time). The threshold for significance was set at 0.05 level. When baseline differences between groups were observed, analysis of covariance results were used with the baseline scores as the covariate. The Tukey-Kramer post hoc tests were used to locate differences.

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Results

Table 1 shows mean (SD) pre and posttraining data for the selected performance parameters. Both the OKCE and CKCE conditions had significant (p < 0.05) and similar improvements on most performance measures. The OKCE group improved 1RM leg press by 35.7 kg, with a 23.0-kg increase in the CKCE group (group × time interaction, p = 0.13). The OKCE group improved 1RM bench press by 5.6 kg, with an 4.0-kg increase in the CKCE group (group × time interaction, p = 0.36).

Table 1

Table 1

Figures 2 and 3 show the individual responses for 1RM leg and bench press, respectively. There was a significant group × time interaction (p = 0.003) for sling exercise push-ups. The CKCE group improved by 148.5%, with an observed mean 11% increase in the OKCE group. Individual responses are shown in Figure 4.

Figure 2

Figure 2

Figure 3

Figure 3

Figure 4

Figure 4

For most Biodex measures, including PT and PP, there were significant increases seen in both groups posttraining for knee extension (p = 0.002 [PT], p = 0.003 [PP]), knee flexion (p = 0.003 [PT], p < 0.001 [PP]), and shoulder internal rotation (p < 0.001 [PT], p < 0.001 [PP]). Shoulder external rotation did not have a significant group effect (p = 0.25 [PT], p = 0.08 [PP]). There were no significant differences between groups.

There was a significant improvement in lateral step-down performance posttraining with no significant differences between groups in both the right and left legs (p < 0.001).

Strength training had little overall effect on anterior, posteromedial, and posterolateral direction performance on the SEBT. For both the right and left legs, there was not a significant difference between pre and posttraining performance on the anterior direction of the SEBT (p = 0.16 [RL], p = 0.90 [LL]). For the right leg, there was also no significant difference between pre and posttraining performances on the posteromedial direction (p = 0.10), but for the left leg, there was an increase in the posteromedial direction (p = 0.003). For the right leg in the posterolateral direction, overall improvement approached significance (p = 0.067), whereas there was a significant increase in reach in the posterolateral direction for the left leg (p = 0.023). Additionally, posterolateral measurements trended toward a group × time interaction, with CKCE eliciting more improvement than OKCE (p = 0.085 [LL], p = 0.12 [RL]).

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Discussion

This study compared the effectiveness of CKCE training and OKCE training on several strength and balance measures in women initiating a strength training program. The major findings of this study were as follows: (a) both OKCE and CKCE strength training were equally effective for improving traditional measures of strength (e.g., 1 RM, isokinetic power) (Table 1, Figures 2 and 3); (b) only CKCE exercise improved sling exercise push-ups indicating both specificity of training and functional training superiority of CKCE exercise (Table 1, Figure 4); and (c) both OKCE and CKCE strength training elicited similar changes on balance with the exception of the posterolateral direction measure, where posterolateral measurements trended toward a group x time interaction, with CKCE eliciting more improvement than OKCE (Table 1).

The similar improvements in strength between the conditions suggest that solely using CKCE training is equally as effective as OKCE training during the initial phases of strength training. Previous studies have also found that CKCE training elicits strength and performance gains similar to or better than OKCE training (1,3,7,13,16). For example, lower-body CKCE training has been shown to be more effective than OKCE training for improving vertical jump performance (1,3,13), and CKCE training generates muscular co-contraction, resulting in greater joint stability (7,16). Another study found that substituting 4 upper-body CKCE was as effective as OKCE training in producing maximal strength gains (13). To our knowledge, this is the first study to examine the effectiveness of a strength training program that uses CKCEs exclusively.

It is interesting to note that the changes observed in strength outcomes after training were similar between groups, despite the fact that the Redcord group had higher initial strength values after random assignment. One could hypothesize that individuals who were less strong to begin would be more likely to experience great change in strength with training (14). It is possible that if subjects started with similar initial strength values, we might have observed greater improvements with CKCEs, similar to what has been observed in previous studies (1,3,6,7,10,11,13,16).

These findings have important implications for women initiating a weight training program, showing that CKCEs can be substituted for OKCEs without a detrimental effect on strength. Women initiating weight training programs are often hesitant to begin an OKCE program because of intimidation and fear of a weight room (8). These women may be more inclined to undertake a CKCE training program that can be conducted outside of a weight room. Further, a CKCE that uses a Redcord device are beneficial because it removes several barriers to strength training. The Redcord device is a convenient and effective strength training device that is portable, and time efficient, which eliminates the time factor that is a barrier for many people trying to consistently strength train (15).

Our hypothesis that performance on CKCE would improve more with CKCE training was supported. The significant group × time interaction for sling exercise push-ups shows that specificity of training impacts performance. The subjects in the CKCE training group used inherently unstable sling-based equipment, which likely activated both core and stabilizing muscles to a greater extent, and led to an improvement in performance. In a recent study from our laboratory (13), we investigated the relationship between strength training method and throwing velocity. That study reported that subjects in the CKCE training group significantly improved throwing velocity compared to the subjects in the OKCE training group, despite similar improvements in maximal strength. The instability of the sling-based training method again likely enhanced activation of the musculature involved in the torso and shoulder stabilization. The activation of these muscles along with more time spent on the eccentric portion of a given exercise could have contributed to the improvement in throwing velocity (13). Through core activation and activation of smaller stabilizing muscles, CKCE sling-based strength training appears to develop functional strength more so than OKCE training, which is beneficial for both performance and everyday living.

This study shows similar changes in balance for CKCE and OKCE training on the SEBT, with the exception of the posterolateral direction. Both strength training methods resulted in a significant improvement for left leg balance in the posteromedial direction and marginally significant improvements for right leg balance in the posteromedial direction. There was no significant change in balance in the anterior direction in both legs. The improvement in the posteromedial direction was expected. Movement in the posteromedial direction is a functional movement and recruits both the quadriceps and hamstrings; thus, strength training is expected to improve performance on this measure (5). The lack of change in anterior balance was not expected. The anterior component of the SEBT is mostly quadriceps dependent, demonstrated by significant quadriceps electromyographic activation during this task (5). Thus, with strength training, specifically quadriceps strength training, performance on the anterior component of the SEBT has been shown to improve (5). We do not have an explanation at this time for the lack of training effect for both the CKCE and OKCE training groups.

Our hypothesis that performance on balance measures would improve more with CKCE training was supported in the posterolateral direction on the SEBT. Our hypothesis was based on the idea that the extra demands CKCEs place on core stability would help with balance performance. Given the rotational component of the posterolateral direction, it is possible that the CKCEs facilitated more recruitment strategies and core stabilization, allowing for more controlled pelvic rotation (5). It is reasonable to hypothesize that CKCE training develops better joint coupling at the hip and knee than OKCE training, allowing for more stable pelvic rotation and core stabilization during the SEBT. In conclusion, both CKCE training and OKCE training for 13 weeks significantly improved overall strength and balance in women beginning weight training.

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Practical Applications

On the basis of the current data, it can be concluded that CKCE training is equally as effective as OKCE training in eliciting improvements during the initial phases of a strength training program in women starting a strength training program. The fact that only CKCEs improved sling exercise push-ups supports previous findings suggesting functional superiority of CKCEs. Further, women beginning strength training are often hesitant to begin an OKCE program because of intimidation and fear of a weight room. These women may be more inclined to undertake a CKCE training program that can be conducted outside of a weight room and can substitute CKCEs for OKCEs without a detrimental effect on strength. Although only beginners were examined, data from this study and data from previous studies indicate that substituting sling-based CKCEs for traditional OKCEs is effective for both strength gains and functional improvement.

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References

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Keywords:

closed-kinetic chain; open-kinetic chain; Redcord; 1RM; isokinetic dynamometry; balance

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