Rubber-based resistance (RBR) bands and standard link steel (SLS) chains are 2 forms of resistances that offer a variable training stimulus. Both forms are used by athletes, strength and conditioning professionals, and in rehabilitation. Resistive properties of rubber-based resistance band and SLS chain are similar in that resistance increases with deformation and displacement, respectively. However, one resistance type increases in a curvilinear (RBR) manner and the other in a linear (SLS chains) fashion. Rubber-based resistance bands are viscoelastic (i.e., a material that behaves mechanically, as a fluid and solid), and thus they exhibit both elastic and nonelastic resistance properties when deformed or stretched (17). Tension (resistance) in RBR bands is determined by the stiffness (stress-strain relationship) properties, which are in turn affected by a number of factors (24). These factors include the type of material used during production, resting length (RL), density, band width, cross-sectional area, rate of deformation, temperature, and humidity. Past studies have confirmed the existence of the linear and curvilinear tension-deformation regions and relationships for RBR bands, which are dependent upon the amount of stress or force applied to, and resultant strain/deformation occurring within, the respective rubber band (12,18,22,24). The resistance provided by SLS chains is gravity dependent and determined by the type of steel, density, diameter, and length of the chain used. Two previous studies have calculated length to weight ratios for various sized (diameter) chains assuming that each link was of the same weight; therefore, linear increases in resistance would occur over changing displacement (1,5).
Rubber-based resistance bands and SLS chains have been used in combination with free weight resistance modes to improve upper and lower body strengths and power in ascending strength curve exercises (e.g., bench press, deadlift, squat, and shoulder press) (2,4,21,24). Strength curves approximate the torque (relationship between force generation and joint angle) production capabilities for specified exercise movements (13). In ascending strength curve exercises, maximum strength and torque production occur near the apex of the lift; therefore, the addition of either RBR bands or SLS chains to a barbell should theoretically provide progressively increasing resistance curves to match the changing torque capabilities of the musculoskeletal system (10,14,15,17). The added tension from the RBR bands and SLS chains has the potential to increase muscle stimulation, motor unit recruitment, and firing rates (6,9,24). Rubber-based resistance bands have also been used in rotator cuff rehabilitation, assisted and resisted sprint training, and powerlifting training to help athletes overcome the sticking region (8,11,16,19,21,23). Standard link steel chains have been used for the clean and snatch in an attempt to improve explosiveness, but there is little empirical evidence to support such a contention (5-7). The use of RBR and SLS chains has also been reported to increase activation of stabilizing muscles and enhance neurological adaptations, but there is a lack of scientific proof to support these claims (6,7).
An inherent limitation when using these modes of resistance is quantifying the actual resistive load. Many practitioners use these types of resistance with little understanding of the magnitude of the overload that the muscle is being exposed to. This is partly attributed to the difficulty in actually performing this type of “calibration” because typically strain gauges and force plates are needed. This difficulty in load prescription can also be attributed to the lack of standardization in regards to the type and quality of rubber and steel used during production. Therefore, the first step before any training with these types of resistance should be to develop tension-deformation charts for RBR bands and mass-displacement charts for SLS chains, because it would allow clinicians and practitioners to prescribe specific loading intensities in a more exact and scientific manner. The purpose of this study was to develop charts displaying the tension-deformation and mass-displacement relationships of RBR bands and SLS chains by quantifying the force outputs associated with these modes measured as a function of displacement and assess the reliability of these measurements. The outcomes of this study may provide clinicians and practitioners with a method of identifying tension-deformation and mass-displacement relationships and the ability to prescribe specific loading intensities.
Experimental Approach to the Problem
The tension and mass properties of RBR bands (Iron Woody LLC, Olney, MT, USA) and SLS chains (Australian Commercial Marine, Fremantle, Western Australia) were quantified statically over a range of displacements. The reliability of the tension of the RBR bands and the mass of the SLS chains were assessed over 4 testing sessions using 2 different force measuring devices (force plate and load cell). A force plate was used to measure the vertical ground reaction force (VGRF) provided by sets of RBR bands and SLS chains between a displacement range of 100-150 cm, where the tension and mass of the RBR bands and SLS chains was transferred to a barbell and squat rack, which in turn applied a VGRF to a force plate. The tension/mass measurements were limited to a displacement range (100-150 cm) of 50 cm because of height restrictions of the adjustable squat rack and the RLs of the RBR bands (104 ± 2.4 cm). A load cell was also used to measure the tension/force of individual RBR bands and SLS chains. The load cell setup allowed for single band and chain measurements, and tension to be assessed over a wider displacement range (100-200 cm) as compared with the force plate. The inner displacement range of 100 cm was chosen because of band RLs, and the outer range of 200 cm was chosen because of band fracture/breaking points.
Five sets of SLS anchor chains (Commercial Marine, Fremantle, Western Australia) with diameters of 6, 8, 10, 13, and 16 mm (Figure 1) and 5 sets of RBR bands (Iron Woody LLC) with widths of 14, 22, 30, 48, and 67 mm (Figure 2) were used in this study. Average chain lengths (260 ± 2.1 cm) and rubber band RLs (104 ± 2.4 cm) were measured before testing. An adjustable squat rack (Model TBP61, Orbit, Perth, Australia), a power cage and light weight barbell (Keiser, Fresno, CA, USA), 2 customized collars, 2 bolts, a tape measure, a vertical stand and a force plate (Fitness Technology, Adelaide, South Australia) were used to quantify the VGRF of RBR band and SLS chain sets. A load cell (Model 1000-DBBP, Bongshin), a measurement display screen (Ranger 2100, Bongshin), 2 eye bolts, 2 karabiners, 2 U bolts, 30 cm of inelastic rope, a tape measure, a vertical stand, and a power rack pulley system were used to quantify the tension and force properties of individual RBR bands and SLS chains.
Testing was performed over 4 sessions, which were divided into 2 force plate and 2 load cell testing sessions to assess reliability within and between devices.
Force Plate Testing
The force plate testing procedures were adapted from Wallace et al. (24). The apparatus/system was comprised of an adjustable squat rack and a light weight barbell, which was placed on a force plate inside a Keiser power cage. A tape measure was fixed vertically to a 2-m stand, which measured the vertical displacement of the barbell. The weight of the system (squat rack and barbell) was offset by zeroing the force plate before each trial; therefore, only the mass/tension of the corresponding sets of SLS chains (6, 8, 10, 13, and 16 mm) and RBR bands (14, 22, 30, 48, and 67 mm) were measured. Ground reaction forces were sampled for 5 seconds at a rate of 200 Hz at each displacement interval. Information was stored in the Ballistic Measurement Software (Fitness Technology, Adelaide, South Australia) data acquisition program.
Force Plate Testing for Rubber-Based Resistance Bands
Sets of equal sized rubber bands (14, 22, 30, 48, and 67 mm) were looped over a light weight barbell at opposite sides of the bar; the free (hanging) ends were then hooked to a sliding pulley system on the base of the power cage via bolts (Figures 3 and 4). Static band tensions (measured as ground reaction forces by the force plate) were acquired at the following displacement intervals: 110, 120, 130, 140, and 150 cm by adjusting the height of the squat rack before each trial. This procedure was replicated over 2 testing sessions to assess within-device reliability.
Force Plate Testing for Standard Link Steel Chains
Sets of equal sized chains (6, 8, 10, 13, and 16) were attached to opposite sides of a light weight barbell via U bolts, and the free ends were coiled on the ground (Figures 5 and 6). Static forces were acquired at the following displacement intervals: 110, 120, 130, 140, and 150 cm by adjusting the height of the squat rack before each trial. This procedure was replicated over 2 testing sessions to assess within-device reliability.
Load Cell Testing
Load Cell Testing for Rubber-Based Resistance Bands
The load cell testing procedures were adapted from Thomas et al. (22) (Figure 7). During the assessment of the RBR bands, the load cell was fixed to the base of the power rack via 2 U bolts, a karabiner and a specialized eye bolt, which was screwed into the load cell. The proximal end of the RBR band was then attached to the load cell via an inelastic rope, a karabiner and a specialized eye bolt, which was screwed into the distal side of the load cell (Figure 8A). The distal (free) end of the RBR band was then looped around the light weight barbell (Figure 8B), and static tensions were measured in 10-cm increments between a displacement range of 100 and 200 cm. The bands were held statically until a stable reading was acquired (∼5 seconds). This procedure was replicated over 2 testing sessions to assess within-device reliability.
Load Cell Testing for Standard Link Steel Chains
One end of a single SLS chain was attached inferior to the load cell in the following sequence: chain, to karabiner, to specialized eye bolt, to load cell; the remainder of the chain was coiled on the ground (Figure 9A, B). The superior portion of the load cell was attached to a pulley system via a specialized eye bolt and a karabiner, which moved vertically from the ground to the top of the power rack (Figure 10). A tape measure was secured vertically to a 2-m stand, and static force was measured as the load cell was moved vertically away from the ground in 10-cm increments between a displacement range of 100-200 cm. This procedure was replicated over 2 testing sessions to assess within-device reliability.
The reliability of SLS chains and RBR bands was assessed using intraclass correlation coefficients (ICCs), standard error of measurements (SEMs), and percent standard error of measurements (SEM %) as calculated by a Microsoft Excel spreadsheet. A paired sample t-test was used to determine if the force plate and load cell differed significantly (p ≤ 0.05). A paired sample t-test was also used to determine if the RBR bands within-set tensions differed significantly (SPSS 14 for Windows). Trend lines were fitted to the data, and goodness of fit (R2) was calculated for each of the resistances using linear and curvilinear regression equations (SPSS 14 for Windows).
The results were delimited to the specific chain properties supplied by Australian Commercial Marine and rubber band tensile properties supplied by Iron Woody LLC. It can be observed from Figures 11 and 12, that the RBR bands were best represented by second-order polynomial functions (R2 ≥ 0.99), exhibiting curvilinear tension-deformation relationships (Table 1); the SLS chains were best represented by first-order polynomial functions, exhibiting linear mass-displacement relationships (R2 = 1) (Table 2). The tension-deformation values of the 5 sets of RBR bands (14, 22, 30, 48, and 67 mm) and the mass-displacement values of the 5 sets of SLS chains (6, 8, 10, 13, and 16 mm) are detailed in Tables 3 and 4.
In terms of interband reliability, the 5 sets of RBR bands were found to be stable between testing sessions (ICC ≥ 0.99) with absolute SEM values ranging from 0.316 kg (SEM % = 5.97) for the 14-mm-wide band to 0.692 kg (SEM % = 2.47%) for the 67-mm-wide band. The mean tension values and RL measurements of the 14-, 22-, and 48-mm bands were more stable than the 30- and 67-mm bands (Table 5).
Interband mean tension values were not significantly different (p > 0.05), but practical differences were evident in the 30 (mean diff = 1.75 kg) and 67-mm (mean difference = 4.9 kg) bands. Resting length measurements were also found to differ for the 30- (RL difference = 3.5 cm) and 67-mm (RL difference = 5.5 cm) bands.
The intertrial measurements were reliable (ICC ≥ 0.99) for all RBR sets (14, 22, 30, 48, and 67 mm). The force plate (lowest SEM = 0.05 kg; mean SEM = 0.13 kg; highest SEM = 0.22 kg) and the load cell (lowest SEM = 0.12 kg; mean SEM = 0.16 kg; highest SEM = 0.21 kg) had similar SEM values over 2 trials. Interdevice measurements (ICC ≥ 0.99; 0.15 ≤ SEM ≤ 0.45 kg) were highly reliable for the all sets of RBR bands, and no significant differences (p > 0.05) were found between devices.
With regards to the chains, the interchain (ICC ≥ 0.999; 0 ≤ SEM ≤ 0.04 kg), intertrial (R ≥ 0.999; SEM = 0.16 kg) and interdevice (R ≥ 0.98; 0.09 ≤ SEM ≤ 0.99 kg) measurements for the 5 sets of SLS chains were highly reliable.
Static tension and weight properties of RBR bands and SLS chains over varying deformations and displacements were established. It was observed that the 5 sets of RBR bands exhibited curvilinear tension-deformation relationships that were best fitted by second-order polynomial function equations (Figure 11 and Table 1), which is similar to those of previous research (24). Some studies have found that RBR bands supplied by other manufacturers exhibited both curvilinear and linear tension-deformation regions (12,18,20,23). The 5 sets of SLS chains exhibited linear mass-displacement relationships and were best fitted by linear function equations (Figure 12 and Table 2), which is expected based on previous research and the material properties of SLS chains. A limitation to the quadratic (second-order polynomial function) equations was the high standard error of the coefficients (Table 1), for example, the measured tension of the 67-mm-wide band set at a 130 cm of deformation was 40 kg, and the predicted value from the quadratic equation was 46.7 kg indicating that these equations should not be used to predict specific tension values but instead be used as trend indicators. Standard coefficient errors would be reduced by measuring RBR tension in smaller intervals (i.e., 1 cm), which in turn would provide more data points and therefore a more accurate regression curve and equation to fit the data. Another option to reduce error is to use both quadratic and linear equations to represent specific portions of the tension-deformation curves, because RBR bands are made of a viscoelastic material (i.e., exhibit both linear and curvilinear stress-strain properties). The linear function equations were accurate predictors of the mass-displacement relationship of SLS chains, shown by the low standard error of coefficients (Table 2).
In terms of reproducing resistance properties over 2 trials, the RBR bands (SEM = 0.15) and SLS chains (SEM = 0.16) were found to be statistically reliable (ICC ≥ 0.99). The load cell and portable force plate testing setups were practically identical (ICC = 0.99) in terms of producing similar force outputs. The load cell testing setup (22) was the most effective method to measure single band and single chain forces. The force plate testing setup (24) was used effectively to measure the VGRF of RBR band and SLS chain sets. The RBR bands (ICC ≥ 0.99; 0.316 kg ≤ SEM ≤ 0.692 kg) and SLS chains (ICC = 1; SEM = 0) produced statistically reliable within-set forces. However, the interband tensile forces were unreliable, and differences were apparent in the 30-mm-wide (tensile diff. = 1.1 kg; RL diff. = 3.5 cm) and 67-mm-wide (tensile diff. = 4.9 kg; RL diff. = 5.5 cm) sets. This variability between bands can be attributed to the differences in interband RLs rather than the material quality of the bands. Therefore, these sets of RBR bands would create an imbalance if added to any barbell based movement (e.g., bench press, squats, deadlift, shoulder press), as they would provide greater resistance to one side of the bar. This imbalance would overload one area of the musculoskeletal system more than the other and could increase the risk of injury and be detrimental to symmetrical muscular development. The 14-, 22-, and 48-mm RBR band sets, and the 5 sets of SLS chains were found to be reliable, with the force outputs differing by less than 1 kg. Those using RBR need to be aware of RL anomalies when purchasing bands, because the RL of the bands can have a substantial effect on the nature of the resistive load.
The RBR bands used in this study were made of a hydrocarbon polymer-based material and exhibited viscoelastic tensile properties, which were dependent on the density, width, thickness, cross-sectional area, RL, and change in deformation of the respective band. The greater the density, width, thickness, cross-sectional area, and deformation of the RBR band, the greater the tensile force. Tensile properties of rubber bands will vary between manufacturers because of these physical/material differences; therefore, tensile/deformation measurements should be provided by all manufacturers and should be recalculated if used in experimental research. The tensile and material properties of the RBR bands used in this study were not provided by the manufacturer but were measured through controlled testing procedures. The resistance bands measured in this study exhibited tension-deformation characteristics similar to other manufacturers' bands that have been measured in past studies (12,18,20,22).
Standard link steel chains are generally comprised of iron, carbon, manganese, and nickel, where tensile strength is dependent on the percentage of carbon used to harden the iron (3). The element composition percentages of the SLS chains used in this study were not provided by the manufacturer. The resistance supplied by the SLS chains was dependent on chain diameter and vertical displacement and can be observed in Table 2. The composition of elements creating SLS chains may vary between manufacturers; therefore, mass-displacement charts specific to the material properties of the different types of SLS chains should be provided by the manufacturers to assist the practitioner in determining the resistive properties and subsequent magnitude of load to be prescribed.
The tension of the RBR bands and the mass of the SLS chains were measured statically at specific displacement intervals and not dynamically at given velocities/loading rates. This could prove to be a limitation, because resistance training and sports-specific movements are dynamic in nature; therefore, the resistance provided by the RBR bands and SLS chains may be different between static and dynamic testing conditions. Future research should be conducted where the resistive forces of these materials are tested at velocities and accelerations specific to sport and exercise movements.
The principal applications of this study for strength and conditioners or clinicians that use these types of resistance are as follows: (a) The load cell and the force plate provided practically identical values; therefore, if practitioners wanted to quantify the resistive forces associated with RBR bands and/or SLS chains, either device would be suitable with the load cell being a relatively cheap and affordable alternative to the force plate. (b) The tension-deformation and mass-displacement charts developed for the products used in this study enable specific loading intensities (i.e., amount of resistance) to be predicted at specific positions throughout an exercises range of motion. (c) It should be noted that the products supplied by other manufacturers will most probably differ in these relationships. It is therefore recommended that manufacturers provide this information; otherwise, those using chains and bands will have little understanding of the magnitude of the resistive overload they are prescribing or have to undertake analysis similar to that detailed in this study. (d) In the case of RBR, the practitioner also needs to be aware that even though the same colored bands are meant to have similar resistive qualities, this is not the case if RLs are different, as was the case for 2 of the band sets used in this study. Careful checking of the RL of bands is needed if the overload to be prescribed is to be standardized.
We thanks the Exercise and Sports Science Department at Edith Cowan University. The results of this study do not constitute endorsement of the product by the authors or by the NSCA.
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Keywords:© 2010 National Strength and Conditioning Association
material properties; standard link steel chains; variable resistance; biomechanics