S. Jun Son

Efficacy of Sensory Transcutaneous Electrical Nerve Stimulation on Perceived Pain and Gait Patterns in Individuals With Experimental Knee Pain

OBJECTIVES To examine the effect of experimental knee pain on perceived knee pain and gait patterns and to examine the efficacy of transcutaneous electrical nerve stimulation (TENS) on perceived knee pain and pain-induced knee gait mechanics. DESIGN Crossover trial. SETTING Biomechanics laboratory. PARTICIPANTS Recreationally active, individuals without musculoskeletal pain aged 18 to 35 years (N=30). INTERVENTIONS Thirty able-bodied individuals were assigned to either a TENS (n=15) or a placebo (n=15) group. All participants completed 3 experimental sessions in a counterbalanced order separated by 2 days: (1) hypertonic saline infusion (5% NaCl); (2) isotonic saline infusion (0.9% NaCl); and (3) control. Each group received sensory electrical stimulation or placebo treatment for 20 minutes, respectively. MAIN OUTCOME MEASURES Perceived pain was collected every 2 minutes using a 10-cm visual analog scale (VAS) for 50 minutes and analyzed using a mixed model analysis of covariance with repeated measures. Gait analyses were performed at baseline, infusion, and treatment. Sagittal and frontal knee angles and internal net joint torque across the entire stance were analyzed using a functional data analysis approach. RESULTS Hypertonic saline infusion increased perceived pain (4/10cm on a VAS; P<.05) and altered right knee angle (more flexion and less abduction; P<.05) and internal net joint torque (less extension and greater abduction; P<.05) across various stance phases. TENS treatment reduced perceived pain and improved right sagittal gait abnormalities as compared with placebo treatment (P<.05). CONCLUSIONS This pain model increases perceived pain and induces compensatory gait patterns in a way that indicates potential quadriceps weakness. However, TENS treatment effectively reduces perceived pain and restores pain-induced gait abnormalities in sagittal knee mechanics.

A 6-week Strength Training Increases Muscle Size in Patients with Chronic Ankle Instability: MRI Analysis

PURPOSE: Despite suggestions that low-intensity (LI) blood flow restricted exercise (BFRE) may be as effective as high intensity (HI) resistance exercise for the purpose of enhancing the recruitment of type II motor units (MU); individual MU acute response to LI BFRE has never been observed and/or reported. Recently, the decomposition of the surface electromyographic (EMG) signals introduced new analysis methods to assess single MU properties. Through these methods we aimed to observe LI BFRE effects on the behavior of the individual MUs. METHODS: Eight men (26.0 ± 3.8 yrs) performed 5 sets of 15 reps of knee extensions at 20% 1RM (with and without BFR). BFR condition was set at 60% of the individual absolute arterial occlusion value. Torque was determined during preand post-exercise maximal voluntary contractions (MVC). Surface EMG activity was recorded from the vastus lateralis (VL) at preand post-exercise time point measurements. In each of these time points, isometric voluntary contractions were performed, matching trapezoidal target-force trajectories at 40% pre-MVC. Resulting surface EMG signals were decomposed and MU recruitment threshold, firing rates and MU action potential (MUAP) amplitudes were further analyzed. RESULTS: Torque only decreased after the LI BFRE condition (-20.5%; p<0.05). In the regression lines between MU recruitment threshold and firing rate, LI BFRE induced higher decrements in the linear slope coefficient (-165.1% ± 120.4, p<0.05) when compared to LI condition (-44.4 ± 33.1, p<0.05). Also, the MU firing rate vs. MUAP amplitude relationship had a notable shift to higher firing rate and MUAP amplitude values after the BFRE condition, reinforcing the evidence that new MUs with higher MUAP amplitude are recruited and MUs with similar MUAP amplitudes are activated at higher firing rates. CONCLUSION: LI BFRE induced a significant change in the MU recruitment pattern, with higher-threshold and lower-firing rate MUs being recruited earlier to compensate muscle failure. Moreover, there were strong evidences about an elevated firing rate in similar MUAP amplitude after LI BFRE condition. Acknowledgements: The authors would like to express their gratitude to Dr. Paola Contessa (Delsys Inc., Natick, USA), for all the invaluable assistance, comments and support.

Walking mechanics for patellofemoral pain subjects with similar self-reported pain levels can differ based upon neuromuscular activation

Patellofemoral pain (PFP) is often studied on subjects who are classified using only self-reported data. Neuromuscular activation influences movement mechanics for PFP subjects, but is not likely to be self-reported. We compared lower-extremity mechanics, during a common movement (walking), between two subdivisions of a group of PFP subjects that were similar, based on common self-report tools, but different, based on a common objective measure of quadriceps activation. Our intent was to highlight the importance of objectively considering neuromuscular activation when researching PFP movement mechanics. Thirty similar PFP research subjects (based on four common self-report tools) were divided into two subdivisions, based on different quadriceps central activation ratios (CAR): a quadriceps deficit (QD; CAR <0.95) group and a no quadriceps deficit (NQD; CAR ≥0.95) group. All subjects in both groups performed five walking trials, while common mechanical characteristics were measured: 3D ground reaction force, and 3D joint kinematics and kinetics. Functional statistics were used to compare mechanical characteristics between the groups across the entire stance phase of gait (α=0.05). Numerous differences were found between the two groups for ground reaction force, and joint kinematics and kinetics. For example, the NQD group exhibited 5% greater vertical ground reaction force at peak impact, and 5% less vertical ground reaction force during the unloading portion of stance, relative to the QD group. The results indicate that when researching movement mechanics associated with PFP, it is important to consider objectively-measured neuromuscular activation characteristics that are not likely to be self-reported by PFP subjects.