1. Marian Abowd, Dr. Cindy Trowbridge, Dr. Mark Ricard EFFECTS OF PATTERNED ELECTRICAL NEUROMUSCULAR STIMULATION ON KNEE JOINT STABILIZATION AbstractResultsConclusion Department of Kinesiology, Biomechanics Laboratory University of Texas at Arlington Introduction INTRODUCTION: Electrical stimulation has traditionally been used in rehabilitation settings for neuromuscular reeducation and to reverse the adverse effects of muscle atrophy. However a more functional form of stimulation, known as patterned electrical neuromuscular stimulation (PENS), has recently been developed to replicate typical firing patterns of muscles. There has been evidence to suggest that receiving this treatment while performing exercises may have the potential to improve functional performance in healthy individuals. PURPOSE: The purpose of this study was to examine the effects of patterned electrical nerve stimulation (PENS) treatment applied during a step-up exercise on knee stabilization during resisted strength and balance tasks. METHODS: Four females and one male volunteered to participate in this study. Subjects were randomly assigned into two groups, one receiving the PENS treatment or “Microcurrent” treatment (control/sham). Each subject met 8 times for familiarization, pre- testing, treatments and post-testing. Subjects received five 15-minute treatments while performing 3x15 step-ups on their left leg. Testing required subjects to attach a cord to their right ankle while resisting 15% of their body weight. They performed five pulls extending their hip backward and five pulls flexing their hip forward. Joint angles at the left hip and left knee and cord force tension were assessed at maximum, middle, and minimum cord tension. Alpha value was set at.05 to test for significance. RESULTS: For the back and front pull at the three sampled time points, there were no significant joint angle differences (p> 0.05) for abduction and adduction, internal and external rotation for hip and knee, hip flexion and extension, or cord force. There were several group x time interactions for knee flexion. For back pull at max tension there were pre to post differences for both the control and PENS group (F (1, 3) = 42.121, p=.007). The control group increased knee flexion by 6.8º±1.6º whereas the PENS group decreased knee flexion 6.7º±1.3º. For the front pull at minimum tension there were pre to post differences for both the control group and the PENS group (F (1, 3) = 13.352, p=.035). The control group increased knee flexion by 8.73º±3.146º whereas the PENS group decreased knee flexion by 6.1º±2.5º. CONCLUSION: We believe that the PENS group decreased knee flexion at the maximum tension for the back pull and minimum tension for the front pull suggesting that the PENS treatment may have increased eccentric control of the quadriceps by improving motor unit recruitment. A more functional form of electrical stimulation, known as patterned electrical neuromuscular stimulation (PENS), has recently been developed to replicate typical firing patterns of muscles. There has been evidence to suggest that receiving this treatment while performing exercises may have the potential to improve functional performance in healthy individuals. It is theorized that increased neuromuscular control at the knee would be useful in preventing knee injuries caused by force flexion (landing) and the subsequent over activation of the knee extensors which can cause an ACL tear. Methods Five healthy subjects met eight times for familiarization of protocol, pre and post testing, and treatments (Table 1 & figure 1). Subjects were randomly assigned to treatment groups. On day 3, 4, 5, 6 and 7 subjects received a 15 minute treatment on the left quadriceps and hamstrings while performing 3x15 step-ups on the left leg (fig. 2). Three subjects received the PENS treatment and two subjects received a sham treatment (fig. 3). Day 3 and day 8 were used to asses kinematics of the stabilizing leg while performing 5 resisted front and back pulls (fig. 4). A SportCordz® and load cell were used to set resistance to 15% of the subject’s body weight. Vicon© cameras, a 6 degrees-of-freedom lower body marker set and Visual 3D software (fig. 5) were used to determine joint angles. Figure 1: Timeline of subjects’ visits Figure 2: Treatment day Figure 3: Accelerated Care Plus Omnistim FX 2 Pro Sport Figure 4: Subject performing a back pull Purpose The purpose of this study was to examine the effects of patterned electrical nerve stimulation (PENS) treatment applied during a step- up exercise on knee kinematics during resisted strength and balance tasks. Height (cm)Weight (kg)Age (yrs) CONTROL 170.18±17.7879.83±29.0324.5±0 PENS 162.56±4.1455.64±3.9925±6.37 Table 1: Demographics BACK MAX (deg) BACK MID (deg) BACK MIN (deg) Pre-test CONTROL29.2±6.334.4±8.439.3±17.2 PENS*42.4±2.541.0±7.146.3±11.3 Post-test CONTROL36.0±9.438.1±20.144.0±17.2 PENS*35.6±1.335.0±10.139.4±13.9 FRONT MAX (deg) FRONT MID (deg) FRONT MIN(deg) Pre-test CONTROL35.7±7.533.0±10.136.4±9.4 PENS47.9±8.244.2±6.9*49.0±6.6 Post-test CONTROL43.1±13.441.2±14.845.1±11.1 PENS45.1±11.138.2±6.5*42.9±4.9 The decreased knee flexion for the PENS group in both the back pull at maximum tension and the front pull at minimum tension suggests the electrical stimulation improved neuromuscular control by increasing eccentric control of the quadriceps through improved joint position. At these two time points, the left knee is typically being pulled into flexion due to direction of core force, gravity, and subject’s desire to control and stabilize motion. Therefore, the quadriceps are activating to control excessive flexion and falling. These findings are relevant in preventing knee injuries that result from forced flexion. Suggestions for future research include: larger sample size, more treatments, and force plate and electromyography (EMG) data collection. Figure 5: Back pull at maximum tension in Visual 3D Figure 6: Front pull at minimum tension in Workspace * Figure 6: Mean knee flexion angles during the back pull at max cord tension. For the PENS group there was a significant decrease in flexion in post test (p=0.007). Figure 7: Mean knee flexion angles during the front pull at min cord tension. For the PENS group there was a significant decrease in flexion in post test (p=0.035). Table 3: Mean knee flexion angles for the three time points during the front pull. *For the PENS group there was a significant decrease in flexion in post test (p=0.035). Table 2: Mean knee flexion angles for the three time points during the back pull. *For the PENS group there was a significant decrease in flexion in post test (p=0.007). Back Max (N)Front Min (N) Cord Force Tension Pre-test122.38±19.2258.37±7.25 Post-test123.17±19.8855.24±11.46 Table 4: Grand mean cord force tension for the back pull at maximum tension and front pull at minimum tension.