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Hyunjae Jeon and Abbey C. Thomas

Clinical Question: Is it beneficial to utilize feedback motion retraining in improving gait biomechanics, pain, and self-reported function on patients with patellofemoral pain (PFP)? Clinical Bottom Line: There is sufficient evidence to support the use of feedback motion retraining to improve gait, pain, and function in PFP rehabilitation.

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Abbey C. Thomas, Scott G. McLean, and Riann M. Palmieri-Smith

Neuromuscular fatigue exacerbates abnormal landing strategies, which may increase noncontact anterior cruciate ligament (ACL) injury risk. The synergistic actions of quadriceps and hamstrings (QH) muscles are central to an upright landing posture, though the precise effect of simultaneous fatigue of these muscles on landing and ACL injury risk is unclear. Elucidating neuromechanical responses to QH fatigue thus appears important in developing more targeted fatigue-resistance intervention strategies. The current study thus aimed to examine the effects of QH fatigue on lower extremity neuromechanics during dynamic activity. Twenty-five healthy male and female volunteers performed three single-leg forward hops onto a force platform before and after QH fatigue. Fatigue was induced through sets of alternating QH concentric contractions, on an isokinetic dynamometer, until the first five repetitions of a set were performed at least 50% below QH peak torque. Three-dimensional hip and knee kinematics and normalized (body mass × height) kinetic variables were quantified for pre- and postfatigue landings and subsequently analyzed by way of repeated- measures mixed-model ANOVAs. QH fatigue produced significant increases in initial contact (IC) hip internal rotation and knee extension and external rotation angles (p < .05), with the increases in knee extension and external rotation being maintained at the time of peak vertical ground reaction force (vGRF) (p < .05). Larger knee extension and smaller knee fexion and external rotation moments were also evident at peak vGRF following fatigue (p < .05). Females landed with greater hip fexion and less abduction than males at both IC and peak vGRF as well as greater knee fexion at peak vGRF (p < .05). The peak vGRF was larger for females than males (p < .05). No sex × fatigue effects were found (p > .05). Fatigue of the QH muscles altered hip and knee neuromechanics, which may increase the risk of ACL injury. Prevention programs should incorporate methods aimed at countering QH fatigue.

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Abbey C. Thomas, Brian G. Pietrosimone, and Carter J. Bayer

Context: Transcranial magnetic stimulation (TMS) may provide important information regarding the corticospinal mechanisms that may contribute to the neuromuscular activation impairments. Paired-pulse TMS testing is a reliable method for measuring intracortical facilitation and inhibition; however, little evidence exists regarding agreement of these measures in the quadriceps. Objective: To determine the between-sessions and interrater agreement of intracortical excitability (short- and long-interval intracortical inhibition [SICI, LICI] and intracortical facilitation [ICF]) in the dominant-limb quadriceps. Design: Reliability study. Setting: Research laboratory. Participants: 13 healthy volunteers (n = 6 women; age 24.7 ± 2.1 y; height 1.7 ± 0.1 m; mass 77.1 ± 17.4 kg). Intervention: Participants completed 2 TMS sessions separated by 1 wk. Main Outcome Measures: Two investigators measured quadriceps SICI, LICI, and ICF at rest and actively (5% of maximal voluntary isometric contraction). All participants were seated in a dynamometer with the knee flexed to 90°. Intracortical-excitability paradigm and investigator order were randomized. Bland-Altman analyses were used to establish agreement. Results: Agreement was stronger between sessions within a single investigator than between investigators and for active than resting measures. Agreement was strongest for resting SICI and active ICF and LICI between sessions for each investigator. Conclusions: Quadriceps intracortical excitability may be measured longitudinally by a single investigator, though active muscle contraction should be elicited during testing.

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Hyunjae Jeon, Sean Krysak, Steven J. Pfeiffer, and Abbey C. Thomas

Second anterior cruciate ligament (ACL) injury has similar biomechanical risk factors as primary injury. Standard of care rehabilitation does not adequately mitigate these biomechanical risks. This study examined the effectiveness of a 4-week plyometric intervention on biomechanical risk factors of second ACL injury versus no intervention in patients with a history of ACL reconstruction. Thirty adults post-ACL reconstruction received 12 sessions of plyometric (age: 19.9 ± 1.62 years; body mass index: 23.9 ± 2.6 kg/m2; months postoperative: 35.7 ± 24.2) or no (age: 21.3 ± 3.5 years; body mass index: 27.7 ± 4.8 kg/m2; months postoperative: 45.3 ± 25.4) exercise intervention. Hip and knee biomechanics were quantified during a jump-landing task before and after the intervention. Individual response to the intervention was evaluated via minimal detectable change. Hip flexion angle had the greatest response to plyometric training. Overall, focused plyometric intervention did not adequately mitigate biomechanical risk factors of second ACL injury; thus, development of interventions capable of modifying biomechanics known to contribute to ACL injury risk remains necessary.

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Hayley M. Ericksen, Brian Pietrosimone, Phillip A. Gribble, and Abbey C. Thomas

Context: Feedback is an important factor in interventions designed to reduce anterior cruciate ligament injury risk. Self-analysis feedback requires participants to self-critique their jump-landing mechanics; however, it is unknown if individuals can effectively self-analyze their own biomechanics and if this self-analysis agrees with observed biomechanical changes by an expert. Objective: To determine agreement between an expert and participants on biomechanical errors committed during 3 of 12 sessions, which were part of an intervention to change jump-landing biomechanics in healthy females. Design: Descriptive analysis. Setting: Research laboratory. Patients or Other Participants: Healthy recreationally active females with no history of lower-extremity fracture or surgery. Interventions: Participants completed a 4-week, 12-session feedback intervention. Each intervention session lasted approximately 15 minutes and included asking participants to perform 6 sets of 6 jumps off a 30-cm-high box placed 50% of their height away from the target landing area. Participants performed self-analysis feedback and received expert feedback on 7 different jump-landing criteria following each set of jumps. Main Outcome Measures: Data were coded, and agreement between the expert and the participant was assessed using Cohen’s unweighted kappa for sessions 1, 6, and 12. Results: There was agreement between the expert and participants for 0/7 criteria for session 1, 3/7 criteria for session 6, and 4/7 criteria for session 12. Conclusions: Participants demonstrated some agreement with the expert when evaluating their jump-landing biomechanics. Self-analysis feedback may not replace what an expert can provide; both types of feedback may be better used in conjunction to produce significant biomechanical changes. Changes made by the participant may not translate into biomechanical changes during a real-life game or practice situation. Future research should continue to investigate effective interventions to reduce injury risk.

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Mohammad H. Izadi Farhadi, Foad Seidi, Hooman Minoonejad, and Abbey C. Thomas

Context: Many factors have been reported contributing to altering the neuromuscular function of hip and knee muscles. The lumbar hyperlordosis, as a poor posture in some athletes, is thought to be associated with the alteration of the hip and knee muscles activity. Objective: To examine the activation of selected hip and knee muscles in athletes with and without lumbar hyperlordosis during functional activities. Design: Case-control study. Setting: University laboratory. Participants: Twenty-six college male athletes (n = 13 with and n = 13 without lumbar hyperlordosis). Interventions: Surface electromyography of gluteus maximus (GMAX), gluteus medius (GMED), vastus medialis oblique (VMO), and vastus lateralis (VL) were recorded during single-leg squat and single-leg jump landing (SLJL) tasks. Main Outcome Measure: Preactivity; reactivity; and onset muscle during SLJL and eccentric activity during single-leg squat (GMAX, GMED, VMO, and VL along with the ratio of VMO:VL) were assessed. Results: Athletes with lumbar hyperlordosis had a higher level of activity in their GMAX (P = .003), VMO (P = .04), and VL (P = .01) muscles at the moment before foot contact during SLJL. These athletes also demonstrated a higher level of GMAX activity (P = .01) immediately after foot contact. Finally, athletes with lumbar hyperlordosis activated their GMAX sooner (P = .02) during the SLJL. Athletes with normal lumbar lordosis had more activity in their GMED muscle (P = .001) in the descending phase of the single-leg squat task and a higher VMO:VL (P = .01) at the moment after the foot contact during the SLJL. Conclusion: The altered activation of GMAX, GMED, VMO, VL, and VMO:VL can reveal the role of lumbar hyperlordosis in the knee and hip muscles’ alteration in athletes. Further study is needed to identify whether these alterations in the hip and knee muscles contribute to injury in athletes.

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Lindsey K. Lepley, Abbey C. Thomas, Scott G. McLean, and Riann M. Palmieri-Smith


As individuals returning to activity after anterior cruciate ligament reconstruction (ACLr) likely experience fatigue, understanding how fatigue affects knee-muscle activation patterns during sport-like maneuvers is of clinical importance. Fatigue has been suggested to impair neuromuscular control strategies. As a result, fatigue may place ACLr patients at increased risk of developing posttraumatic osteoarthritis (OA).


To determine the effects of fatigue on knee-muscle activity post-ACLr.


Case control.


University laboratory.


12 individuals 7–10 mo post-ACLr (7 male, 5 female; age 22.1 ± 4.7 y; 1.8 ± 0.1 m; mass 77.7 ± 11.9 kg) and 13 controls (4 male, 9 female; age 22.9 ± 4.3 y; 1.7 ± 0.1 m; mass 66.9 ± 9.8 kg).


Fatigue was induced via repetitive sets of double-leg squats (n = 8), which were interspersed with sets of single-leg landings (n = 3), until squats were no longer possible.

Main Outcome Measures:

2 × 2 repeated-measures ANOVA was used to detect the main effects of group (ACLr, control) and fatigue state (prefatigue, postfatigue) on quadriceps:hamstring cocontraction index (Q:H CCI).


All subjects demonstrated higher Q:H CCI at prefatigue compared with postfatigue (F 1,23 = 66.949, P ≤ .001). Q:H CCI did not differ between groups (F 1,23 = 0.599, P = .447).


The results indicate that regardless of fatigue state, ACLr individuals are capable of restoring muscle-activation patterns similar to those in healthy subjects. As a result, excessive muscle cocontraction, which has been hypothesized as a potential mechanism of posttraumatic OA, may not contribute to joint degeneration after ACLr.

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Abbey C. Thomas, Janet E. Simon, Rachel Evans, Michael J. Turner, Luzita I. Vela, and Phillip A. Gribble

Context: Knee osteoarthritis (OA) frequently develops following knee injury/surgery. It is accepted that knee injury/surgery precipitates OA with previous studies examining this link in terms of years after injury/surgery. However, postinjury OA prevalence has not been examined by decade of life; thereby, limiting our understanding of the age at which patients are diagnosed with posttraumatic knee OA. Objective: Evaluate the association between the knee injury and/or surgical history, present age, and history of receiving a diagnosis of knee OA. Design: Cross-sectional survey. Setting: Online survey. Participants: A total of 3660 adults were recruited through ResearchMatch©. Of these, 1723 (47.1%) were included for analysis due to history of (1) knee surgery (SURG: n = 276; age = 53.8 [15.3] y; and body mass index [BMI] = 29.9 [8.0] kg/m2), (2) nonsurgical knee injury (INJ: n = 449; age = 46.0 [15.6] y; and BMI = 27.5 [6.9] kg/m2), or (3) no knee injury (CTRL: n = 998; age = 44.0 [25.2] y; and BMI = 26.9 [6.6] kg/m2). Respondents were subdivided by decade of life (20–29 through 70+). Intervention: An electronic survey regarding knee injury history, treatment, and diagnosis of knee OA. Main Outcome Measures: Binary logistic regression determined the association between knee surgical status and OA by decade of life. Participants with no histories of OA or lower-extremity injury were the referent categories. BMI was a covariate in all analyses. Results: SURG respondents were more likely to report having knee OA than CTRL for all age groups (odds ratios: 11.43–53.03; P < .001). INJ respondents aged 30 years and older were more likely to have OA than CTRL (odds ratios: 2.99–14.22; P < .04). BMI influenced associations for respondents in their 50s (P = .001) and 60s (P < .001) only. Conclusions: INJ increased the odds of reporting a physician diagnosis of knee OA in adults as young as 30 to 39 years. Importantly, SURG yielded 3 to 4 times greater odds of being diagnosed with knee OA compared with INJ in adults as young as 20 to 29 years. Delaying disease onset in these young adults is imperative to optimize the quality of life long term after surgery.

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Hayley M. Ericksen, Caitlin Lefevre, Brittney A. Luc-Harkey, Abbey C. Thomas, Phillip A. Gribble, and Brian Pietrosimone

Context: High vertical ground reaction force (vGRF) when initiating ground contact during jump landing is one biomechanical factor that may increase risk of anterior cruciate ligament injury. Intervention programs have been developed to decrease vGRF to reduce injury risk, yet generating high forces is still critical for performing dynamic activities such as a vertical jump task. Objective: To evaluate if a jump-landing feedback intervention, cueing a decrease in vGRF, would impair vertical jump performance in a separate task (Vertmax). Design: Randomized controlled trial. Patients (or Other Participants): Forty-eight recreationally active females (feedback: n = 31; 19.63 [1.54] y, 1.6 [0.08] cm, 58.13 [7.84] kg and control: n = 15; 19.6 [1.68] y, 1.64 [0.05] cm, 60.11 [8.36] kg) participated in this study. Intervention: Peak vGRF during a jump landing and Vertmax were recorded at baseline and 4 weeks post. The feedback group participated in 12 sessions over the 4-week period consisting of feedback provided for 6 sets of 6 jumps off a 30-cm box. The control group was instructed to return to the lab 28 days following the baseline measurements. Main Outcome Measures: Change scores (postbaseline) were calculated for peak vGRF and Vertmax. Group differences were evaluated for peak vGRF and Vertmax using a Mann–Whitney U test (P < .05). Results: There were no significant differences between groups at baseline (P > .05). The feedback group (−0.5 [0.3] N/kg) demonstrated a greater decrease in vGRF compared with the control group (0.01 [0.3] N/kg) (t(46) = −5.52, P < .001). There were no significant differences in change in Vertmax between groups (feedback = 0.9 [2.2] cm, control = 0.06 [2.1] cm; t(46) = 0.46, P = .64). Conclusions: While the feedback intervention was effective in decreasing vGRF when landing from a jump, these participants did not demonstrate changes in vertical jump performance when assessed during a different task. Practitioners should consider implementing feedback intervention programs to reduce peak vGRF, without worry of diminished vertical jump performance.