Context: Medial knee displacement (MKD) is a common risk factor for lower-extremity injury and is related to altered gluteal muscle activity. Ultrasound imaging (USI) is a reliable means to explore mechanical muscle activity; however, no information exists regarding USI of the gluteals during gait in an MKD population. Objective: To determine differences in USI gluteal muscle activity during gait in individuals with and without MKD. Design: Descriptive laboratory study. Setting: University research laboratory. Participants: Out of 28 participants, 14 exhibiting MKD unilaterally during a single-leg squat (19.36 [1.51] y, 169.73 [7.50] cm, and 62.01 [10.57] kg; 10 females) and 14 matched non-MKD subjects (20.29 [1.73] y, 167.24 [9.07] cm, and 67.53 [16.03] kg). Interventions: Bilateral B-mode USI of the gluteus maximus (Gmax) and gluteus medius (Gmed) muscles during quiet stance, heel strike, and a 10-second treadmill walking clip. Main Outcome Measures: Gluteal thickness measures normalized to quiet stance yielded activity ratios, and percentage of muscle thickness change was assessed between heel strike and quiet stance. Differences between groups were assessed with Cohen’s d effect sizes with 95% confidence intervals. Activity ratios with 90% confidence intervals plotted on 10% intervals from 0% to 100% of gait were used to compare groups and limbs. A subsample of images was measured to determine intertester reliability. Results: USI revealed decreased Gmax and Gmed percent change at heel strike (%change = −9.57% [7.15%] and −8.76% [4.26%], respectively). The MKD limb compared with the contralateral limb exhibited decreased Gmed activity ratio at 30% of gait (MKD = 0.89 [0.056]; non-MKD = 1.01 [.052]). Intertester reliability was excellent for gluteus maximus (intraclass correlation coefficient = .987 [.014]) and Gmed (intraclass correlation coefficient = .989 [.013]) measurements. Conclusions: USI highlighted gluteal activity differences of MKD limbs during gait, which may contribute to inadequate hip stabilization during this daily repetitive task. These findings potentiate the use of USI as an intervention- or screening-based visual tool.
Alexandra F. DeJong, L. Colby Mangum, Jacob E. Resch, and Susan A. Saliba
Mark A. Sutherlin, L. Colby Mangum, Jay Hertel, Susan A. Saliba, and Joseph M. Hart
Ultrasound imaging has been used to assess muscle function of deeper muscles and to compare individuals with and without low back pain. These measures may be influenced by numerous factors requiring normalization for these comparisons. The purpose of this study was to assess anthropometric normalization variables with muscle thickness of the transversus abdominis and lumbar multifidus across multiple ultrasound testing positions. Numerous anthropometric variables were correlated with muscle thickness. Mass, body mass index, and height times mass show the best promise for normalization, but were not consistent for the transversus abdominis and lumbar multifidus muscles. Normalization strategies should be considered when comparing between groups.
Mark A. Sutherlin, L. Colby Mangum, Shawn Russell, Susan Saliba, Jay Hertel, and Joe M. Hart
Context: Reduced spinal stabilization, delayed onset of muscle activation, and increased knee joint stiffness have been reported in individuals with a history of low back pain (LBP). Biomechanical adaptations resulting from LBP may increase the risk for future injury due to suboptimal loading of the lower-extremity or lumbar spine. Assessing landing mechanics in these individuals could help identify which structures might be susceptible to future injury. Objective: To compare vertical and joint stiffness of the lower-extremity and lumbar spine between individuals with and without a previous history of LBP. Design: Cross-sectional study. Setting: Research laboratory. Participants: There were 45 participants (24 without a previous history of LBP—age 23  y, height 169.0 [8.5] cm, mass 69.8 [13.8] kg; 21 with a previous history of LBP—age 25 y, height 170.0 [8.0] cm, mass 70.2 [11.8] kg). Interventions: Single-limb landing trials on the dominant and nondominant limb from a 30-cm box. Main Outcome Measures: Vertical stiffness and joint stiffness of the ankle, knee, hip, and lumbar spine. Results: Individuals with a previous history of LBP had lower vertical stiffness (P = .04), but not joint stiffness measures compared with those without a previous history of LBP (P > .05). Overall females had lower vertical (P = .01), ankle (P = .02), and hip stiffness (P = .04) compared with males among all participants. Males with a previous history of LBP had lower vertical stiffness compared with males without a previous history LBP (P = .01). Among all individuals without a previous history of LBP, females had lower vertical (P < .01) and ankle stiffness measures (P = .04) compared with males. Conclusions: Landing stiffness may differ among males and females and a previous history of LBP. Comparisons between individuals with and without previous LBP should be considered when assessing landing strategies, and future research should focus on how LBP impacts landing mechanics.
Luk Devorski, David M. Bazett-Jones, L. Colby Mangum, and Neal R. Glaviano
Context: Lumbopelvic-hip complex (LPHC) exercises are used to increase stabilization within the human body. Torso-elevated side support (TESS), foot-elevated side support (FESS), prone bridge plank (PBP), and V-sit are common LPHC exercises. Objective: To evaluate muscle activation in the shoulder girdle and LPHC during 4 LPHC exercises and evaluate the reasoning for termination. Study Design: Cross-sectional study. Setting: Laboratory. Patients or Other Participants: Seventeen healthy participants (12 males and 5 females; age: 21.47 [3.16] y, height: 179.73 [8.92] cm, mass: 76.89 [11.17] kg). Main Outcome Measures: Participants completed 2 repetitions of the TESS, FESS, PBP, and V-sit until failure. Surface electromyography of the middle deltoid, latissimus dorsi, middle trapezius, rectus abdominis, erector spinae, external oblique, and gluteus medius were recorded and normalized to maximum voluntary isometric contraction (MVIC). The duration of exercise and subjective reasoning for termination of exercise was completed following the 4 tasks. Results: The TESS and PBP had significantly greater middle deltoid muscle activation (TESS: 55.66% [24.45%] MVIC and PBP: 42.63% [18.25%] MVIC) compared with the FESS (10.10% [10.04%] MVIC) and V-sit (2.21% [1.94%] MVIC), P < .05. The TESS produced significantly greater external oblique activity (78.13% [32.32%] MVIC) than the PBP (54.99% [19.54%] MVIC), P < .05. Due to shoulder fatigue and pain, 41.1% and 17.0% of participants terminated the TESS, respectively. The PBP was terminated due to abdominal fatigue (41.1%) and upper-extremity fatigue (47.0%). Conclusions: The V-sit resulted in isolated activity of the abdominal portion of the LPHC. The FESS had increased global co-contraction of the LPHC compared with the TESS. The PBP and TESS had significant muscle activation in the upper-extremity.
Neal R. Glaviano, Ashley N. Marshall, L. Colby Mangum, Joseph M. Hart, Jay Hertel, Shawn Russell, and Susan Saliba
Context: Patellofemoral pain (PFP) is a challenging condition, with altered kinematics and muscle activity as 2 common impairments. Single applications of patterned electrical neuromuscular stimulation (PENS) have improved both kinematics and muscle activity in females with PFP; however, the use of PENS in conjunction with a rehabilitation program has not been evaluated. Objective: To determine the effects of a 4-week rehabilitation program with PENS on lower-extremity biomechanics and electromyography (EMG) during a single-leg squat (SLS) and a step-down task (SDT) in individuals with PFP. Study Design: Double-blinded randomized controlled trial. Setting: Laboratory. Patients of Other Participants: Sixteen females with PFP (age 23.3 [4.9] y, mass 66.3 [13.5] kg, height 166.1 [5.9] cm). Intervention: Patients completed a 4-week supervised rehabilitation program with or without PENS. Main Outcome Measures: Curve analyses for lower-extremity kinematics and EMG activity (gluteus maximus, gluteus medius, vastus medialis oblique, vastus lateralis, biceps femoris, and adductor longus) were constructed by plotting group means and 90% confidence intervals throughout 100% of each task, before and after the rehabilitation program. Mean differences (MDs) and SDs were calculated where statistical differences were identified. Results: No differences at baseline in lower-extremity kinematics or EMG were found between groups. Following rehabilitation, the PENS group had significant reduction in hip adduction between 29% and 47% of the SLS (MD = 4.62° [3.85°]) and between 43% and 69% of the SDT (MD = 6.55° [0.77°]). Throughout the entire SDT, there was a decrease in trunk flexion in the PENS group (MD = 10.91° [1.73°]). A significant decrease in gluteus medius activity was seen during both the SLS (MD = 2.77 [3.58]) and SDT (MD = 4.36 [5.38]), and gluteus maximus during the SLS (MD = 1.49 [1.46]). No differences were seen in the Sham group lower-extremity kinematics for either task. Conclusion: Rehabilitation with PENS improved kinematics in both tasks and decreased EMG activity. This suggests that rehabilitation with PENS may improve muscle function during functional tasks.
Kristen Couper Schellhase, Emily Tran, Shannon Carmody, Peter Dawry, and L. Colby Mangum
Research has explored factors related to retention of athletic trainers in collegiate settings but less is known about retention of athletic trainers in secondary school settings. This study aimed to investigate factors that increase retention of secondary school athletic trainers. Twenty-two secondary school athletic trainers (10 females and 12 males, length of employment 14.65 ± 5.01 years) participated in a semistructured video call interview with seven open-ended questions. A phenomenological approach revealed three themes and eight subthemes: (a) support (administration, partner athletic trainer, and non-work-related); (b) connections (impact on patients, school community, and wider community); and (c) security (financial and nonfinancial). Although participants acknowledged challenges, they identified aspects that positively influenced their retention.