Evaluation of an Innovative Shoulder Strengthening Device: Reactively Training the Shoulder

Authors

Bradley T. Hirayama, University of the PacificFollow
Jamie Narciso, University of the PacificFollow
Shadi Othman, University of the PacificFollow
Preeti Oza, University of the PacificFollow

Poster Number

5a

Lead Author Affiliation

Engineering Science

Lead Author Status

Masters Student

Second Author Affiliation

Bioengineering

Third Author Affiliation

Bioengineering Department

Third Author Status

Faculty

Fourth Author Affiliation

Physical Therapy

Fourth Author Status

Faculty

Introduction/Abstract

According to the 2016 United States Bureau of Labor report, approximately 32 shoulder injury cases were reported per 10,000 full time employees, equating to a median of 26 days away from work – more than double any other body part (Alizadehkhaiyat, Hawkes, Kemp, & Frostick, 2015). A 2006 national comparative study of US high school athletic trainers revealed that the shoulder joint was the most prevalent injury for both males and females across 9 different sports resulting in approximately 44% of the injured players missing multiple weeks of playing time (Arora, Button, Basset, & Behm, 2013). Additionally, the Phoenix shoulder and knee clinic reported in 2006 that approximately four million orthopedic visits were for the rotator cuff or other shoulder problems, and that about 25 percent of people over fifty have some sort of shoulder issue (i.e. pain, rotator cuff, etc.) (Phoenix Shoulder and Knee, 2014). Clearly, the shoulder has been and remains a part of the body that is prone to injury and causes numerous lost days of work and school within the United States, yet shoulder strengthening and rehabilitation innovations have been a stagnant area of study yielding only a few known published articles within the past five years (our search in Scopus and PubMed resulted in less than five publications). These studies focused on post-surgery individuals’ rehabilitation applications, quantifying muscle activities and best current rehabilitation/strengthening exercises (Alizadehkhaiyat, Hawkes, Kemp, & Frostick, 2015; Arora, Button, Basset, & Behm, 2013; Escamilla, et al., 2016; Meyers, et al., 2005). Additionally, current rehabilitation devices such as the Bodyblade (Escamilla, et al., 2016) or resistance bands (Meyers, et al., 2005), do not allow injured or weaker athletes proper strengthening or rehabilitation. This is due to the patient’s limited strength, which may lead to a longer or incomplete rehabilitation time. The focus of this article is to define sports related injury biomechanics, introduce innovative strengthening and rehabilitation technology, then provide a comprehensive study of one innovation, ROTR 1, that is designed to reactively strengthen (Reilly, Cabri, & Araujo, 2005) the muscles of the shoulder using a mechanized system.

Purpose

Reactive strengthening, the ability for the body to change quickly from an eccentric to a concentric contraction, is a technique used to effectively increase performance in activities such as basketball and sprinting (Reilly, Cabri, & Araujo, 2005). This strengthening technique focuses on proper muscular contraction during action to produce the maximum force and protection for the joints. Current shoulder strengthening and rehabilitation devices, however, aren’t focused on proper muscle recruitment to maximize performance and protection. Escamilla et al. describes the use of the BB as an oscillating pattern that can be used in various positions (Escamilla, et al., 2016). The user provided oscillation and movement patterns of the BB and resisted against the motion to keep the BB in an equilibrium state to activate the muscles of the shoulder complex. In this study, an innovative device, Rotr 1 (patent pending), was created to use dynamic, mechanically created motion to disturb the balance of muscular forces around the shoulder. The device creates a random force, provided by motor driven oscillations, that the user must keep in an equilibrium state. The main goal of the Rotr 1 is to use a reactive style of strengthening of the shoulder complex that increases the body’s ability to adapt and protect the shoulder in various situations.

Method

A total of 17 healthy volunteers, 10 non-athletes and 7 athletes, participated in the study. All participants didn’t have any current or previous shoulder injuries, past surgeries, or any possible ailments that may change the biomechanics of the shoulder. They were recruited from the general student body at The University of the Pacific. The mean (±STD) height, weight, and age for the entire group was 66.8±4.3 in, 148.6±35.6 lbs, and 21.2±1.7 years. This study was approved by the University’s institutional review board (IRB) and each participant gave written informed consent prior to participation. Subjects were asked to wear comfortable shorts, no shoes, and no shirt (sports bra for females). The electrode placement areas were prepped by shaving and abrading prior to placement of the electrodes. Eight wireless Delsys electrodes were placed parallel to the fibers of each muscle studied on the subject’s dominant side adapted from Criswell et al (Criswell & Cram, 2011). Standard OptiTrack calibration and baseline markers were used for this study. The device was tested in three different positions (figure 1). The positions were represent the progression of the throwing motion. Four configurations in each position were tested to determine the efficacy of the device (table 1). The subject had no prior knowledge or use of the device before starting the study. All exercises were performed seated with their feet firmly planted on the floor. The test administrator instructed and supervised the subjects on the proper use of the device – relaxing the hand and forearm allowing the device to move the entire arm. The device was demonstrated to each subject by the test administrator; however, subjects were not allowed to handle the device in any way prior to the start of testing. The test administrator provided a random ‘jerk’ intensity for each trial to avoid learning or any bias from the subject or administrator. All trials were performed in a single hour session. Once the electrodes were placed on the subject and the motion capture system was calibrated, the subject was instructed to sit on a low, no-back stool. Maximum voluntary isometric contraction (MVIC) data was collected for each muscle as described by the CDC (U.S. Department of Health And Human Services, 1992). Subject was instructed to give their max for 10 seconds, then 30 seconds of rest was given to minimize the effect of fatigue. The MVIC for each subject was performed in the same order: anterior deltoid, middle deltoid, posterior deltoid, bicep, tricep, pectoralis major, latissimus dorsi, and middle trapezius. Once the MVIC was completed, the subject was shown the three positions used in the trial (figure 1) and instructed to practice each position before the test began. Each subject was instructed to do their best to return to the same positions each time using visual and memory cues. Subjects were to assume a random position/configuration (table 1) by the test administrator. A total of 12 position/configurations were used and 3 trials were performed for each. Each trial lasted 10 seconds with a 30 second rest in-between trials. The raw EMG signal was full-wave rectified and smoothed with a 10 ms moving window over the duration of the 10 second trial. The maximum value of the rectified signal was extracted and normalized as percent max of MVIC. Configuration 1, from the table above, was used as my ‘baseline’ muscle activity and my starting point for comparison. A one way Kruskal-Wallis analysis of variance (ANOVA) was employed (p < 0.05) to assess the difference amongst the four configurations for each subject. A two way (2 x 2) fixed measures ANOVA was employed (p < 0.05) to assess the difference amongst the three positions. A two way nested ANVOA was employed (p < 0.05) to assess the interaction for all subjects and between position and configuration. Tukey HSD post-hoc analysis was employed to assess the pairwise comparisons and identify the differences. Motion capture data was exported as x, y, z positional data points for all 37 markers used in each trial. The marker’s data of the proximal and posterior shoulder, upper arm, elbow, wrist and hand of the dominant arm for each subject was organized using R. The data was full wave rectified and sorted into each positional grouping. The standard deviation for each group was calculated and the percentage of points within one standard deviation of the mean was used to indicate the positional accuracy between athletes and non-athletes.

Results

Motion capture data for each position was clustered together and the standard deviation was calculated then plotted, see in figure 2. Athletes were found to have higher positional accuracy (~87% position markers within one standard deviation of mean) than non-athletes (~82% position makers within one standard deviation of mean). The interaction between the fixed variable, position, and the random variable, configuration, had to be assessed before the interaction within each variable (shown in table 2). The anterior deltoid (P=.922), middle deltoid (P=.886), posterior deltoid (P=.999), biceps brachii (P=.999), triceps brachii (P=.999), and latissimus dorsi (P=.988) show no significance between the fixed and random variables; however, the pectoralis major (P=.0006) showed significance between the variables. The non-athletes showed a greater percent activation than the athletes for both males and females in all muscle groups, positions and configurations (figure 3a and 3b). Further investigation of the male and female data separately showed that the average percent activation for athletes and non-athletes are similar in amplitude (e.g. all male non-athlete’s percent activation amplitude are similar). Samples of male (figure 3c) and female (figure 3d) data are presented with progressing configurations on three different muscles and all three positions. An increasing trend is seen between configurations. The magnitude of percent activation between configuration 1 (control) and configuration 4 (working against device) are similar for all trials (~0.1% increase). This increase, however, is not statistically significant (alpha=0.05) using Kruskal-Wallis and two-way ANOVA analysis. A similar trend was found in all other muscles except for the pectoralis major and posterior deltoid. Positional accuracy was found to be extremely important due to the significant difference in muscular activation between positions (figure 3e). Two samples (middle and posterior deltoid) are used to show an approximate 20% difference in activation of the muscles between positions one and three. A similar trend was found for all muscle groups and positions.

Significance

The neuro-muscular system is built to adapt to changes in its environment and react to stimuli. It responds best by learning from errors brought upon the system due to a disturbance of its equilibrium. Current shoulder strengthening and rehabilitation techniques are static and require users to provide, then react to the error in the system. I’ve created an innovative device that uses dynamic, mechanically created motion to disturb the balance of muscular forces around the shoulder. The device creates a random error that the user must react to, increasing the body’s ability to adapt and protect the shoulder in various situations. My device can be used in any arm position and throughout all ranges of motion, making it useful to anyone that performs overhead activities. My experiment was set up to assess the efficacy of the device by correlating the muscular activity using different arm positions and device configurations. The data collection was performed using electromyographical analysis of the muscles around the shoulder; which, demonstrated an increase in muscular activation of the shoulder muscles without requiring significant user input. Static rehabilitation systems are being replaced by dynamic resistance exercises forcing the user to react instead of act, increasing their performance and decreasing the likelihood of injury. Though many devices are being created for dynamic resistance exercises, none have been marketed for the shoulder. I am bridging this gap through my research and have successfully created a dynamic shoulder strengthening and rehabilitation device. I hope to elevate performance of overhead athletes and any overhead activities, by increasing the body’s ability to effectively react and protect the shoulder.

Location

DeRosa University Center

Format

Poster Presentation

Poster Session

Morning 10am-12pm