Muscle coactivation before and after the impact phase of running following isokinetic fatigue

Context:

The effects of fatigue on impact loading during running are unclear, with some authors reporting increased impact forces and others reporting decreased forces.

Objective:

To examine the effects of isokinetic fatigue on muscle cocontraction ratios about the knee and ankle during running.

Design:

Cross-sectional study.

Setting:

Neuromechanics laboratory.

Patients or Other Participants:

Female middle-distance runners (age  =  21.3 ± 1.93 years) with at least 5 years of training experience.

Intervention(s):

Participants ran on the treadmill at 3.61 m/s before and immediately after the fatigue protocol, which consisted of consecutive, concentric knee extension-flexion at 120°/s until they could no longer produce 30% of the maximum knee-extension moment achieved in the familiarization session for 3 consecutive repetitions.

Main Outcome Measure(s):

Electromyographic (EMG) amplitude of the vastus medialis (VM), biceps femoris (BF), gastrocnemius (GAS), and tibialis anterior (TA) was recorded using surface electrodes. Agonist∶antagonist EMG ratios for the knee (VM∶BF) and ankle (GAS∶TA) were calculated for the preactivation (PR), initial loading response (LR₁), and late loading response (LR₂) phases of running. Hip-, knee-, and ankle-joint angular displacements at initial foot contact were obtained from 3-dimensional kinematic tracings.

Results:

Fatigue did not alter the VM∶BF EMG ratio during the PR phase (P > .05), but it increased the ratio during the LR₁ phase (P < .05). The GAS∶TA EMG ratio increased during the LR₁ phase after fatigue (P < .05) but remained unchanged during the PR and LR₂ phrases (P > .05).

Conclusions:

The increased agonist EMG activation, coupled with reduced antagonist EMG activation after impact, indicates that the acute decrease in muscle strength capacity of the knee extensors and flexors results in altered muscle-activation patterns about the knee and ankle before and after foot impact.     

Ankle strength and force sense after a progressive, 6-week strength-training program in people with functional ankle instability

Context:

Although strength training is commonly used to rehabilitate ankle injuries, studies investigating the effects of strength training on proprioception have shown conflicting results.

Objective:

To determine the effects of a 6-week strength-training protocol on force sense and strength development in participants with functional ankle instability.

Design:

Randomized controlled clinical trial.

Setting:

University athletic training research laboratory.

Patients or Other Participants:

A total of 40 participants with functional ankle instability were recruited. They were randomly placed into a training group (10 men, 10 women: age  =  20.9 ± 2.2 years, height  =  76.4 ± 16.1 cm, mass  =  173.0 ± 7.9 kg) or control group (10 men, 10 women: age  =  20.2 ± 2.1 years, height  =  78.8 ± 24.5 cm, mass  =  173.7 ± 8.2 kg).

Intervention(s):

Participants in the training group performed strength exercises with the injured ankle 3 times per week for 6 weeks. The protocol consisted of a combination of rubber exercise bands and the Multiaxial Ankle Exerciser, both clinically accepted strengthening methods for ankle rehabilitation. The progression of this protocol provided increasingly resistive exercise as participants changed either the number of sets or resistance of the Thera-Band or Multiaxial Ankle Exerciser.

Main Outcome Measure(s):

A load cell was used to measure strength and force sense. Inversion and eversion strength was recorded to the nearest 0.01 N. Force-sense reproduction was measured at 2 loads: 20% and 30% of maximal voluntary isometric contraction.

Results:

Increases in inversion (F_1,38  =  11.59, P < 0.01, η_p²  =  0.23, power  =  0.91) and eversion (F_1,38  =  57.68, P < .01, η_p²  =  0.60, power  =  0.99) strength were found in the training group at the posttest when compared with the control group. No significant improvements were noted in force-sense reproduction for either group.

Conclusions:

Strength training at the ankle increased strength but did not improve force sense.     

Emergency face-mask removal effectiveness: a comparison of traditional and nontraditional football helmet face-mask attachment systems

Context:

Football helmet face-mask attachment design changes might affect the effectiveness of face-mask removal.

Objective:

To compare the efficiency of face-mask removal between newly designed and traditional football helmets.

Design:

Controlled laboratory study.

Setting:

Applied biomechanics laboratory.

Participants:

Twenty-five certified athletic trainers.

Intervention(s):

The independent variable was face-mask attachment system on 5 levels: (1) Revolution IQ with Quick Release (QR), (2) Revolution IQ with Quick Release hardware altered (QRAlt), (3) traditional (Trad), (4) traditional with hardware altered (TradAlt), and (5) ION 4D (ION). Participants removed face masks using a cordless screwdriver with a back-up cutting tool or only the cutting tool for the ION. Investigators altered face-mask hardware to unexpectedly challenge participants during removal for traditional and Revolution IQ helmets. Participants completed each condition twice in random order and were blinded to hardware alteration.

Main Outcome Measure(s):

Removal success, removal time, helmet motion, and rating of perceived exertion (RPE). Time and 3-dimensional helmet motion were recorded. If the face mask remained attached at 3 minutes, the trial was categorized as unsuccessful. Participants rated each trial for level of difficulty (RPE). We used repeated-measures analyses of variance (α  =  .05) with follow-up comparisons to test for differences.

Results:

Removal success was 100% (48 of 48) for QR, Trad, and ION; 97.9% (47 of 48) for TradAlt; and 72.9% (35 of 48) for QRAlt. Differences in time for face-mask removal were detected (F_4,20  =  48.87, P  =  .001), with times ranging from 33.96 ± 14.14 seconds for QR to 99.22 ± 20.53 seconds for QRAlt. Differences were found in range of motion during face-mask removal (F_4,20  =  16.25, P  =  .001), with range of motion from 10.10° ± 3.07° for QR to 16.91° ± 5.36° for TradAlt. Differences also were detected in RPE during face-mask removal (F_4,20  =  43.20, P  =  .001), with participants reporting average perceived difficulty ranging from 1.44 ± 1.19 for QR to 3.68 ± 1.70 for TradAlt.

Conclusions:

The QR and Trad trials resulted in superior results. When trials required cutting loop straps, results deteriorated.     

Tibiofemoral Joint Positioning for the Valgus Stress Test

Context:

Recommendations on the positioning of the tibiofemoral joint during a valgus stress test to optimize isolation of the medial collateral ligament (MCL) from other medial joint structures vary in the literature. If a specific amount of flexion could be identified as optimally isolating the MCL, teaching and using the technique would be more consistent in clinical application.

Objective:

To determine the angle of tibiofemoral joint flexion between 0° and 20° that causes a difference in the slope of the force-strain line when measuring the resistance to a valgus force applied to the joint.

Design:

Cross-sectional study.

Setting:

University research laboratory.

Patients or Other Participants:

Twelve healthy volunteers (6 men, 6 women: age  =  26.4 ± 5.6 years, height  =  170.9 ± 8.4 cm, mass  =  75.01 ± 14.6 kg).

Intervention(s):

Using an arthrometer, we applied a valgus force, over a range of 60 N, to the tibiofemoral joint in 0°, 5°, 10°, 15°, and 20° of flexion.

Main Outcome Measure(s):

Force-strain measurements were obtained for 5 positions of tibiofemoral joint flexion.

Results:

As knee flexion angle increased, slope values decreased (F_4,44  =  17.6, P < .001). The slope at full extension was not different from that at 5° of flexion, but it was different from the slopes at angles greater than 10° of flexion. Similarly, the slope at 5° of flexion was not different from that at 10° of flexion, but it was different from the slopes at 15° and 20° of flexion. Further, the slope at 10° of flexion was not different from that at 15° or 20° of flexion. Finally, the slope at 15° of flexion was not different from that at 20° of flexion.

Conclusions:

When performing the manual valgus stress test, the clinician should fully extend the tibiofemoral joint or flex it to 5° to assess all resisting medial tibiofemoral joint structures and again at 15° to 20° of joint flexion to further assess the MCL.     

Comparison of recovery strategies on maximal force-generating capacity and electromyographic activity level of the knee extensor muscles

Context:

With regard to intermittent training exercise, the effects of the mode of recovery on subsequent performance are equivocal.

Objective:

To compare the effects of 3 types of recovery intervention on peak torque (PT) and electromyographic (EMG) activity of the knee extensor muscles after fatiguing isokinetic intermittent concentric exercise.

Design:

Crossover study.

Setting:

Research laboratory.

Patients or Other Participants:

Eight elite judo players (age = 18.4 ± 1.4 years, height = 180 ± 3 cm, mass = 77.0 ± 4.2 kg).

Interventions :

Participants completed 3 randomized sessions within 7 days. Each session consisted of 5 sets of 10 concentric knee extensions at 80% PT at 120°/s, with 3 minutes of recovery between sets. Recovery interventions were passive, active, and electromyostimulation. The PT and maximal EMG activity were recorded simultaneously while participants performed isokinetic dynamometer trials before and 3 minutes after the resistance exercise.

Main Outcome Measure(s):

The PT and maximal EMG activity from the knee extensors were quantified at isokinetic velocities of 60°/s, 120°/s, and 180°/s, with 5 repetitions at each velocity.

Results:

The reduction in PT observed after electromyo-stimulation was less than that seen after passive (P < .001) or active recovery (P < .001). The reduction in PT was less after passive recovery than after active recovery (P < .001). The maximal EMG activity level observed after electromyostimulation was higher than that seen after active recovery (P < .05).

Conclusions:

Electromyostimulation was an effective recovery tool in decreasing neuromuscular fatigue after high-intensity, intermittent isokinetic concentric exercise for the knee extensor muscles. Also, active recovery induced the greatest amount of neuromuscular fatigue.     

Sweat Rates, Sweat Sodium Concentrations, and Sodium Losses in 3 Groups of Professional Football Players

Context:

Sweat sodium losses have never been reported in a large cohort of American football players.

Objective:

To compare sweat rates (SwtRs), sweat sodium concentrations (SwtNa⁺), and sodium losses in 3 groups of players (backs and receivers [BK], linebackers and quarterbacks [LB/QB], and linemen [LM]) to determine if positional differences and, therefore, size differences exist.

Design:

Observational study.

Setting:

Data were collected during practices in the second week of 2 consecutive training camps. The wet bulb globe temperature was 78.5°F ± 3.5°F (25.9°C ± 1.9°C).

Patients or Other Participants:

Eighteen BK, 12 LB/QB, and 14 LM volunteered.

Intervention(s):

Sterile sweat patches were applied to the right forearm after the skin was appropriately cleaned. The patches were removed during practice, placed in sterile tubes, centrifuged, frozen, and later analyzed by flame photometry.

Main Outcome Measure(s):

Sweat rate, SwtNa⁺, and sodium loss. We calculated SwtR by change in mass adjusted for urine produced and fluids consumed divided by practice time in hours.

Results:

Other than age, physical characteristics were different among groups (P < .001). The SwtR was different among groups (F_2,41  =  7.3, P  =  .002). It was lower in BK (1.42 ± 0.45 L/h) than in LB/QB (1.98 ± 0.49 L/h) (P < .05) and LM (2.16 ± 0.75 L/h) (P < .01), but we found no differences between SwtRs for LB/QB and LM. The SwtNa⁺ was not different among groups (BK  =  50 ± 16 mEq/L, LB/QB  =  48.2 ± 23 mEq/L, and LM  =  52.8 ± 25 mEq/L) and ranged from 15 to 99 mEq/L. Sweat sodium losses ranged from 642 mg/h to 6.7 g/h, and findings for group comparisons approached significance (P  =  .06). On days when players practiced 4.5 hours, calculated sodium losses ranged from 2.3 to 30 g/d.

Conclusions:

The BK sweated at lower rates than did the midsized LB/QB and large LM, but LB/QB sweated similarly to LM. Sweat sodium concentration and daily sodium losses ranged considerably. Heavy, salty sweaters require increased dietary consumption of sodium during preseason.     

Self-paced exercise performance in the heat after pre-exercise cold-fluid ingestion

Context:

Precooling is the pre-exercise reduction of body temperature and is an effective method of improving physiologic function and exercise performance in environmental heat. A practical and effective method of precooling suitable for application at athletic venues has not been demonstrated.

Objective:

To confirm the effectiveness of pre-exercise ingestion of cold fluid without fluid ingestion during exercise on pre-exercise core temperature and to determine whether pre-exercise ingestion of cold fluid alone without continued provision of cold fluid during exercise can improve exercise performance in the heat.

Design:

Randomized controlled clinical trial.

Setting:

Environmental chamber at an exercise physiology laboratory that was maintained at 32°C, 60% relative humidity, and 3.2 m/s facing air velocity.

Patients or Other Participants:

Seven male recreational cyclists (age = 21 ± 1.5 years, height = 1.81 ± 0.07 m, mass = 78.4 ± 9.2 kg) participated.

Intervention(s):

Participants ingested 900 mL of cold (2°C) or control (37°C) flavored water in 3 300-mL aliquots over 35 minutes of pre-exercise rest.

Main Outcome Measure(s):

Rectal temperature and thermal comfort before exercise and distance cycled, power output, pacing, rectal temperature, mean skin temperature, heart rate, blood lactate, thermal comfort, perceived exertion, and sweat loss during exercise.

Results:

During rest, a greater decrease in rectal temperature was observed with ingestion of the cold fluid (0.41 ± 0.16°C) than the control fluid (0.17 ± 0.17°C) over 35 to 5 minutes before exercise (t₆ = −3.47, P = .01). During exercise, rectal temperature was lower after ingestion of the cold fluid at 5 to 25 minutes (t₆ range, 2.53–3.38, P ≤ .05). Distance cycled was greater after ingestion of the cold fluid (19.26 ± 2.91 km) than after ingestion of the control fluid (18.72 ± 2.59 km; t₆ = −2.80, P = .03). Mean power output also was greater after ingestion of the cold fluid (275 ± 27 W) than the control fluid (261 ± 22 W; t₆ = −2.13, P = .05). No differences were observed for pacing, mean skin temperature, heart rate, blood lactate, thermal comfort, perceived exertion, and sweat loss (P > .05).

Conclusions:

We demonstrated that pre-exercise ingestion of cold fluid is a simple, effective precooling method suitable for field-based application.     

Cold-Water Immersion and the Treatment of Hyperthermia: Using 38.6��C as a Safe Rectal Temperature Cooling Limit

Context:

Cold-water immersion is recommended for the immediate field treatment of exertional heat stroke. However, concerns exist over potential overcooling of hyperthermic individuals during cold-water immersion.

Objective:

To evaluate the recommendation that removing previously hyperthermic individuals from a cold-water bath at a rectal temperature (T_re) of 38.6°C would attenuate overcooling.

Design:

Controlled laboratory study.

Setting:

University research laboratory.

Patients or Other Participants:

Participants included 6 men and 4 women (age  =  22 ± 3 years, height  =  172 ± 10 cm, mass  =  67.8 ± 10.7 kg, body fat percentage  =  17.1% ± 4.5%, maximum oxygen consumption  =  59.3 ± 8.7 mL·kg⁻¹·min⁻¹).

Intervention(s):

After exercising at an ambient temperature of 40.0°C for 38.5 ± 9.4 minutes, until T_re reached 39.5°C, participants were immersed in a 2.0°C circulated water bath until T_re decreased to either 37.5°C or 38.6°C. Subsequently, participants were removed from the water bath and recovered for 20 minutes at an ambient temperature of 25°C.

Main Outcome Measure(s):

Rectal and esophageal temperatures were measured continuously during the immersion and recovery periods.

Results:

Because of the experimental design, the overall time of immersion was greater during the 37.5°C trial (16.6 ± 5.7 minutes) than the 38.6°C trial (8.8 ± 2.6 minutes) (t₉  =  −4.740, P  =  .001). During the recovery period after cold-water immersion, both rectal (F_1,9  =  50.540, P < .001) and esophageal (F_1,6  =  20.365, P  =  .007) temperatures remained greater in the 38.6°C trial than in the 37.5°C trial. This was evidenced by low points of 36.47°C ± 0.70°C and 37.19°C ± 0.71°C for rectal temperature (t₉  =  2.975, P  =  .016) and of 35.67°C ± 1.27°C and 36.72°C ± 0.95°C for esophageal temperature (t₆  =  3.963, P  =  .007) during the recovery period of the 37.5°C and 38.6°C trials, respectively.

Conclusions:

Immersion for approximately 9 minutes to a rectal temperature cooling limit of 38.6°C negated any risk associated with overcooling hyperthermic individuals when they were immersed in 2°C water.     

An assessment of burnout in graduate assistant certified athletic trainers

Context:

Graduate assistant athletic trainers (GAATs) must balance the demands of clinical care and the academic load of graduate-level students.

Objective:

To examine burnout among GAATs with clinical assistantships at National Collegiate Athletic Association (NCAA) Division I institutions and to identify the personal and situational variables that are related to burnout.

Design:

Cross-sectional study.

Setting:

Division I universities offering graduate assistantship programs.

Patients or Other Participants:

Two hundred one GAATs enrolled at NCAA Division I universities with graduate assistantship positions.

Main Outcome Measures(s):

The Athletic Training Burnout Inventory, which assesses stress and burnout among ATs through 4 constructs: emotional exhaustion and depersonalization, administrative responsibility, time commitment, and organizational support. The 6-point Likert scale is anchored by 1 (never true) and 6 (always true).

Results:

The GAATs who traveled with athletic teams (4.051 ± 0.895) and those who provided classroom instruction (4.333 ± 1.16) reported higher levels of stress due to time commitment than those who did not travel (3.713 ± 1.22) or teach (3.923 ± 0.929). We also found a difference in administrative responsibility across clinical settings (F_6,194  =  3.507, P  =  .003). The results showed that GAATs in NCAA Division I clinical settings (44.55 ± 13.17 hours) worked more hours than those in NCAA Division III clinical settings (33.69 ± 12.07 hours) and those in high school settings (30.51 ± 9.934 hours).

Conclusions:

Graduate assistant ATs are at risk for burnout because of the time necessary to complete their clinical and academic responsibilities and their additional administrative responsibilities. Graduate assistants who work in the Division I clinical setting are at greater risk for burnout than those in the secondary school setting because of the large number of hours required.     

Custom-molded foot-orthosis intervention and multisegment medial foot kinematics during walking

Context:

Foot-orthosis (FO) intervention to prevent and treat numerous lower extremity injuries is widely accepted clinically. However, the results of quantitative gait analyses have been equivocal. The foot models used, participants receiving intervention, and orthoses used might contribute to the variability.

Objective:

To investigate the effect of a custom-molded FO intervention on multisegment medial foot kinematics during walking in participants with low-mobile foot posture.

Design:

Crossover study.

Setting:

University biomechanics and ergonomics laboratory.

Patients or Other Participants:

Sixteen participants with low-mobile foot posture (7 men, 9 women) were assigned randomly to 1 of 2 FO groups.

Interventions :

After a 2-week period to break in the FOs, individuals participated in a gait analysis that consisted of 5 successful walking trials (1.3 to 1.4 m/s) during no-FO and FO conditions.

Main Outcome Measure(s):

Three-dimensional displacements during 4 subphases of stance (loading response, mid-stance, terminal stance, preswing) were computed for each multisegment foot model articulation.

Results:

Repeated-measures analyses of variance (ANOVAs) revealed that rearfoot complex dorsiflexion displacement during midstance was greater in the FO than the no-FO condition (F_1,14 = 5.24, P = .04, partial η² = 0.27). Terminal stance repeated-measures ANOVA results revealed insert-by-insert condition interactions for the first metatarsophalangeal joint complex (F_1,14 = 7.87, P = .01, partial η² = 0.36). However, additional follow-up analysis did not reveal differences between the no-FO and FO conditions for the balanced traditional orthosis (F_1,14 = 4.32, P = .08, partial η² = 0.38) or full-contact orthosis (F_1,14 = 4.10, P = .08, partial η² = 0.37).

Conclusions:

Greater rearfoot complex dorsiflexion during midstance associated with FO intervention may represent improved foot kinematics in people with low-mobile foot postures. Furthermore, FO intervention might partially correct dys-functional kinematic patterns associated with low-mobile foot postures.     

Interday reliability of peak muscular power outputs on an isotonic dynamometer and assessment of active trunk control using the chop and lift tests

Context:

Assessment techniques used to measure functional tasks involving active trunk control are restricted to linear movements that lack the explosive movements and dynamic tasks associated with activities of daily living and sport. Reliable clinical methods used to assess the diagonal and ballistic movements about the trunk are lacking.

Objective:

To assess the interday reliability of peak muscular power outputs while participants performed diagonal chop and lift tests and maintained a stable trunk.

Design:

Controlled laboratory study.

Setting:

University research laboratory.

Patients or Other Participants:

Eighteen healthy individuals (10 men and 8 women; age  =  32 ± 11 years, height  =  168 ± 12 cm, mass  =  80 ± 19 kg) from the general population participated.

Intervention(s):

Participants performed 2 power tests (chop, lift) using an isotonic dynamometer and 3 endurance tests (Biering-Sørensen, side-plank left, side-plank right) to assess active trunk control. Testing was performed on 3 different days separated by at least 1 week. Reliability was compared between days 1 and 2 and between days 2 and 3. Correlations between the power and endurance tests were evaluated to determine the degree of similarity.

Main Outcome Measure(s):

Peak muscular power outputs (watts) derived from a 1-repetition maximum protocol for the chop and lift tests were collected for both the right and left sides.

Results:

Intraclass correlation coefficients for peak muscular power were highly reliable for the chop (range, 0.87–0.98), lift (range, 0.83–0.96), and endurance (range, 0.80–0.98) tests between test sessions. The correlations between the power assessments and the Biering-Sørensen test (r range, −0.008 to 0.017) were low. The side-plank tests were moderately correlated with the chop (r range, 0.528–0.590) and the lift (r range, 0.359–0.467) tests.

Conclusions:

The diagonal chop and lift power protocol generated reliable data and appears to be a dynamic test that simulates functional tasks, which require dynamic trunk control.     

Cooling the neck region during exercise in the heat

Context:

Cooling the neck region can improve the ability to exercise in a hot environment. It might improve performance by dampening the perceived level of thermal strain, allowing individuals to override inhibitory signals.

Objective:

To investigate whether the enhanced ability to exercise in a hot environment observed when cooling the neck region occurs because of dampening the perceived level of thermal strain experienced and the subsequent overriding of inhibitory signals.

Design:

Crossover study.

Setting:

Walk-in environmental chamber.

Patients or Other Participants:

Eight endurance-trained, nonacclimated men (age  =  26 ± 2 years, height  =  1.79 ± 0.04 m, mass  =  77.0 ± 6.2 kg, maximal oxygen uptake [V̇O_2max]  =  56.2 ± 9.2 mL·kg⁻¹·min⁻¹) participated.

Intervention(s):

Participants completed 4 running tests at approximately 70% V̇O_2max to volitional exhaustion: 2 familiarization trials followed by 2 experimental trials (cooling collar [CC] and no collar [NC]). Trials were separated by 7 days. Familiarization and NC trials were performed without a collar and used to assess the test variability.

Main Outcome Measure(s):

Time to volitional exhaustion, heart rate, rectal temperature, neck skin temperature, rating of perceived exertion, thermal sensation, and feeling scale (pleasure/displeasure) were measured.

Results:

Time to volitional exhaustion was increased by 13.5% ± 3.8% (CC  =  43.15 ± 12.82 minutes, NC  =  38.20 ± 11.70 minutes; t₇  =  9.923, P < .001) with the CC, which reduced mean neck skin temperature throughout the test (P < .001). Participants terminated exercise at identical levels of perceived exertion, thermal sensation, and feeling scale, but the CC enabled participants to tolerate higher rectal temperatures (CC  =  39.61°C ± 0.45°C, NC  =  39.18°C ± 0.7°C; t₇  =  −3.217, P  =  .02) and heart rates (CC  =  181 ± 6 beats/min, NC  =  178 ± 9 beats/min; t₇  =  −2.664, P  =  .03) at the point of termination.

Conclusions:

Cooling the neck increased the time taken to reach volitional exhaustion by dampening the perceived levels of thermal strain.     

Balance performance with a cognitive task: a continuation of the dual-task testing paradigm

Context:

To ensure that concussed athletes return to play safely, we need better methods of measuring concussion severity and monitoring concussion resolution.

Objective:

To develop a dual-task model that assesses postural stability and cognitive processing in concussed athletes.

Design:

Repeated measures study.

Setting:

University laboratory.

Patients or Other Participants:

Twenty healthy, college-aged students (10 men, 10 women; age  =  20 ± 1.86 years, height  =  173 ± 4.10 cm, mass  =  71.83 + 35.77 kg).

Intervention(s):

Participants were tested individually in 2 sessions separated by 2 days. In one session, a balance task and a cognitive task were performed separately. In the other session, the balance and cognitive tasks were performed concurrently. The balance task consisted of 6 conditions of the Sensory Organization Test performed on the NeuroCom Smart Balance Master. The cognitive task consisted of an auditory switch task (3 trials per condition, 60 seconds per trial).

Main Outcome Measure(s):

For the balance test, scores for each Sensory Organization Test condition; the visual, vestibular, somatosensory, and visual-conflict subscores; and the composite balance score were calculated. For the cognitive task, response time and accuracy were measured.

Results:

Balance improved during 2 dual-task conditions: fixed support and fixed visual reference (t₁₈  =  −2.34, P < .05) and fixed support and sway visual reference (t₁₈  =  −2.72, P  =  .014). Participants'' response times were longer (F_1,18  =  67.77, P < .001, η²  =  0.79) and choice errors were more numerous under dual-task conditions than under single-task conditions (F_1,18  =  5.58, P  =  .03, η²  =  0.24). However, differences were observed only during category-switch trials.

Conclusions:

Balance was either maintained or improved under dual-task conditions. Thus, postural control took priority over cognitive processing when the tasks were performed concurrently. Furthermore, dual-task conditions can isolate specific mental processes that may be useful for evaluating concussed individuals.     

Core temperature and sweat responses in professional women's tennis players during tournament play in the heat

Context:

Tennis is often played in hot, humid environments, intensifying the thermoregulatory strain placed on the athletes. As a safety measure, some tennis organizations allow for a 10-minute break in play between the second and third sets when environmental conditions are extreme. However, the actual effect of these breaks in reducing core temperature is unknown.

Objective:

To determine change in core temperature after a 10-minute break in play and assess fluid balance in professional female tennis players during tournament matches in the heat.

Design:

Cross-sectional study.

Setting:

A Women''s Tennis Association Tour–sanctioned outdoor tournament on hard courts under hot conditions (30.3°C ± 2.3°C).

Patients or Other Participants:

Seven professional tennis players.

Main Outcome Measure(s):

Change in core temperature after a 10-minute break in tournament play, fluid intake, and sweat losses during match play.

Results:

Core temperature was reduced from 38.92°C to 38.67°C (change of −0.25°C ± 0.20°C) when a break was taken (P  =  .02). Mean sweat rate during match play was 2.0 ± 0.5 L/h. During that time, mean fluid intake was 1.5 ± 0.5 L/h, resulting in a 1.2% ± 1.0% reduction in body mass.

Conclusions:

Female professional tennis players are subjected to high heat loads during match play in hot environments. However, a 10-minute break in play decreased core temperature in 6 of 7 players by an average of 0.25°C, indicating that the break provides practical benefits in the field. Furthermore, although mean sweat rate in this group of female tennis players was high, most athletes were still able to minimize mass loss to less than 2% of their prematch weight.     

Perceived frequency of peer-assisted learning in the laboratory and collegiate clinical settings

Context:

Peer-assisted learning (PAL) has been recommended as an educational strategy to improve students'' skill acquisition and supplement the role of the clinical instructor (CI). How frequently students actually engage in PAL in different settings is unknown.

Objective:

To determine the perceived frequency of planned and unplanned PAL (peer modeling, peer feedback and assessment, peer mentoring) in different settings.

Design:

Cross-sectional study.

Setting:

Laboratory and collegiate clinical settings.

Patients or Other Participants:

A total of 933 students, 84 administrators, and 208 CIs representing 52 (15%) accredited athletic training education programs.

Intervention(s):

Three versions (student, CI, administrator) of the Athletic Training Peer Assisted Learning Survey (AT-PALS) were administered. Cronbach α values ranged from .80 to .90.

Main Outcome Measure(s):

Administrators'' and CIs'' perceived frequency of 3 PAL categories under 2 conditions (planned, unplanned) and in 2 settings (instructional laboratory, collegiate clinical). Self-reported frequency of students'' engagement in 3 categories of PAL in 2 settings.

Results:

Administrators and CIs perceived that unplanned PAL (0.39 ± 0.22) occurred more frequently than planned PAL (0.29 ± 0.19) regardless of category or setting (F_1,282 = 83.48, P < .001). They perceived that PAL occurred more frequently in the collegiate clinical (0.46 ± 0.22) than laboratory (0.21 ± 0.24) setting regardless of condition or category (F_1,282 = 217.17, P < .001). Students reported engaging in PAL more frequently in the collegiate clinical (3.31 ± 0.56) than laboratory (3.26 ± 0.62) setting regardless of category (F_1,860 = 13.40, P < .001). We found a main effect for category (F_2,859 = 1318.02, P < .001), with students reporting they engaged in peer modeling (4.01 ± 0.60) more frequently than peer mentoring (2.99 ± 0.88) (P < .001) and peer assessment and feedback (2.86 ± 0.64) (P < .001).

Conclusions:

Participants perceived that students engage in unplanned PAL in the collegiate clinical setting with a stronger inclination toward engagement in peer modeling. Educators should develop planned PAL activities to capitalize on the inherent desire of the students to collaborate with their peers.