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Caroline Lisee, Lindsay Slater, Jay Hertel and Joe M. Hart

Context: Strength, functional performance, and limb symmetry are common objective clinical assessments used by clinicians to guide safe return to physical activity following injury. Population-specific unilateral limb outcomes or estimates of limb symmetry of these assessments should be established. Objective: To compare lower-extremity strength, functional performance, and limb symmetry in healthy participants based on sex and level of activity. Design: Descriptive laboratory study. Setting: Laboratory. Participants: A total of 117 healthy participants (72 males and 45 females; mass = 73.67 [13.60] kg, height = 1.76 [0.12] m, and age = 21.44 [2.92] y) without history of injury within 6 months were included. Interventions: Participants completed isokinetic concentric and isometric knee extension and flexion strength tasks at 90°/s, 180°/s, and 90°, respectively, and 4 hop tasks (single, cross-over, triple, and 6-m timed) during 1 session. Groups were separated by sex (male and female) and activity level (athlete and nonathlete). Participants rostered on National Collegiate Athletic Association (NCAA) Division I (DI) teams were considered as athletes, and non-NCAA DI healthy, uninjured participants were considered as nonathletes. Main Outcome Measures: Limb symmetry index (LSI), maximal voluntary isometric contraction (N·m/kg), peak torque (N·m/kg), average power (N·m/s), distance (m), and time hopped (s) were assessed. LSI was calculated by dividing the lower limb outcome by the higher limb outcome of the nondominant or dominant limb. Group differences were assessed through Mann–Whitney U tests and Cohen’s d effect sizes for all comparisons. Results: LSI differences did not exist between groups. Mean LSIs for all participants ranged between 83.52% (12.54%) and 96.16% (3.82%). On average, males were stronger (range: d = 0.63–1.54), hopped farther (range: d = 1.52–1.63), and hopped faster (range: d = 1.67–1.68) than females. On average, some strength differences existed between athletes and nonathletes, but athletes hopped farther (range: d = 0.71–0.82) and faster (range: d = 0.87–0.88) than nonathletes. Conclusions: Unilateral limb strength and functional performance outcomes differ between sex and activity level, but not limb symmetry. These differences may be important for a clinician’s understanding of normative values of common return-to-play assessment tasks.

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J. Craig Garrison, Joe M. Hart, Riann M. Palmieri, D. Casey Kerrigan and Christopher D. Ingersoll

Context:

Although kinematic analyses are helpful in describing movement differences between genders, kinetic data might further explain the predisposing factors contributing to potential injury during athletic landing maneuvers.

Objective:

To determine whether there are differences in knee moments between male and female varsity college soccer players during a single-leg landing.

Design:

Preexperimental with static group comparison.

Setting:

Motion-analysis laboratory.

Participants:

16 varsity college soccer players (8 men, 8 women).

Intervention:

Subjects performed 5 single-leg landings from a height of 60 cm.

Main Outcome Measures:

Peak internal rotation, valgus, varus, and extension knee moments calculated from raw ground-reaction forces and kinematic data.

Results:

Significant gender differences were present (P = .020), with men exhibiting 31% greater mean peak knee-varus moments than women when landing on a single leg from 60 cm (P = .020).

Conclusions:

Male soccer players demonstrate greater knee-varus moments than female soccer players during single-leg landing. This might be valuable in designing clinical treatment and prevention programs for ACL injuries.

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Jihong Park, Terry L. Grindstaff, Joe M. Hart, Jay N. Hertel and Christopher D. Ingersoll

Context:

Weight-bearing (WB) and non-weight-bearing (NWB) exercises are commonly used in rehabilitation programs for patients with anterior knee pain (AKP).

Objective:

To determine the immediate effects of isolated WB or NWB knee-extension exercises on quadriceps torque output and activation in individuals with AKP.

Design:

A single-blind randomized controlled trial.

Setting:

Laboratory.

Participants:

30 subjects with self-reported AKP.

Interventions:

Subjects performed a maximal voluntary isometric contraction (MVIC) of the quadriceps (knee at 90°). Maximal voluntary quadriceps activation was quantified using the central activation ratio (CAR): CAR = MVIC/(MVIC + superimposed burst torque). After baseline testing, subjects were randomized to 1 of 3 intervention groups: WB knee extension, NWB knee extension, or control. WB knee-extension exercise was performed as a sling-based exercise, and NWB knee-extension exercise was performed on the Biodex dynamometer. Exercises were performed in 3 sets of 5 repetitions at approximately 55% MVIC. Measurements were obtained at 4 times: baseline and immediately and 15 and 30 min postexercise.

Main Outcome Measures:

Quadriceps torque output (MVIC: N·m/Kg) and quadriceps activation (CAR).

Results:

No significant differences in the maximal voluntary quadriceps torque output (F 2,27 = 0.592, P = .56) or activation (F 2,27 = 0.069, P = .93) were observed among the 3 treatment groups.

Conclusions:

WB and NWB knee-extension exercises did not acutely change quadriceps torque output or activation. It may be necessary to perform exercises over a number of sessions and incorporate other disinhibitory interventions (eg, cryotherapy) to observe acute changes in quadriceps torque and activation.

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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 [8] y, height 169.0 [8.5] cm, mass 69.8 [13.8] kg; 21 with a previous history of LBP—age 25[9] 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.

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J. Craig Garrison, Joe M. Hart, Riann M. Palmieri, D. Casey Kerrigan and Christopher D. Ingersoll

Context:

Gender differences in muscle activity during landing have been studied as a possible contributing factor to the greater incidence of anterior cruciate ligament injuries in women.

Objective:

To compare root-mean-square (RMS) electromyography (EMG) of selected lower extremity muscles at initial contact (IC) and at peak knee internal-rotation (IR) moment in men and women during landing.

Design:

Preexperimental design static-group comparison.

Setting:

Motion-analysis laboratory.

Participants:

16 varsity college soccer players (8 men, 8 women).

Main Outcome Measures:

EMG activity of the gluteus medius, lateral hamstrings, vastus lateralis, and rectus femoris during landing.

Results:

When RMS EMG of all muscles was considered simultaneously, no significant differences were detected between genders at IC or at peak knee IR moment.

Conclusion:

Male and female college soccer players display similar relative muscle activities of the lower extremity during landing. Gender landing-control parameters might vary depending on the technique used to analyze muscle activity.

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Michael L. Alosco, Krysten Knecht, Ellen Glickman, John Gunstad, Michael Bergeron and Joe Hart

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Shandi L. Partner, Mark Alan Sutherlin, Shellie Acocello, Susan A. Saliba, Eric M. Magrum and Joe M. Hart

Context:

Individuals with low back pain (LBP) have reduced function of the transversus abdominis (TrA) and lumbar multifidus (LM) muscles. Biofeedback during exercise may increase the ability to contract the TrA and LM muscles compared with exercise alone.

Objective:

To compare TrA preferential activation ratio (PAR) and the percent change in LM-muscle thickness in patients with LBP history before and after exercise with or without biofeedback.

Design:

Controlled laboratory study.

Setting:

University research laboratory.

Patients:

20 LBP individuals, 10 exercise alone and 10 exercise with biofeedback.

Interventions:

Patients were allotted to tabletop exercises in isolation or tabletop exercises with visual, auditory, and tactile biofeedback.

Main Outcome Measures:

TrA PAR and percent change in LM-muscle thickness.

Results:

There were no differences between groups at baseline (all P > .05). Nonparametric statistics showed decreased resting muscle thickness for total lateral abdominal-wall muscles (P = .007) but not TrA (P = .410) or LM (P = .173). Percent TrA thickness increased from table to standing positions before (P = .006) and after exercise (P = .009). TrA PAR increased after exercise (pre 0.01 ± 0.02, post 0.03 ± 0.04, P = .033) for all patients and for exercise with biofeedback (pre 0.02 ± 0.01, post 0.03 ± 0.01, P = .037) but not for exercise alone (pre 0.01 ± 0.02, post 0.02 ± 0.05, P = .241). No group differences were observed for TrA PAR before (exercise 0.01 ± 0.02, exercise with biofeedback 0.02 ± 0.01, P = .290) or after exercise (exercise 0.02 ± 0.05, exercise with biofeedback 0.03 ± 0.01, P = .174). There were no group differences in LM percent change before exercise (P = .999) or after exercise (P = .597). In addition, no changes were observed in LM percent change as a result of exercise among all participants (P = .391) or for each group (exercise P = .508, exercise with biofeedback P = .575).

Conclusion:

TrA PAR increased after a single session of exercises, whereas no thickness changes occurred in LM.

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Joe Hart, Damien Clement, Jordan Hamson-Utley, Monna Arvinen-Barrow, Cindra Kamphoff, Rebecca A. Zakrajsek and Scott B. Martin

Context:

Injured athletes begin the rehabilitation process with expectations about the nature of the working relationship with an athletic trainer. These expectations can infuence the effectiveness of the assistance provided.

Objective:

To determine whether male and female athletes differed in terms of expectations about injury rehabilitation services with an athletic trainer.

Design:

A questionnaire was administered to student athletes that assessed expectations about injury rehabilitation. Setting: Five colleges and universities.

Patients or Other Participants:

Questionnaire responses were provided by 679 student athletes (443 males and 236 females).

Main Outcome Measure:

Responses to the Expectations about Athletic Training questionnaire were used to assess factors identifed as Personal Commitment, Facilitative Conditions, Athletic Trainer Expertise, and Realism.

Results:

A statistically signifcant interaction between gender and prior experience was identifed. Male athletes with no prior experience had lower expectations for a facilitative environment. Female athletes with prior experience were less likely to have realistic expectations.

Conclusions:

Gender and prior experience infuence athletes’ expectations of injury rehabilitation with an athletic trainer.