Performance on the Single-Legged Step Down and Running Mechanics

ContextPrevious authors have shown associations between kinematics on the single-legged step down (SLSD) and running mechanics. Therefore, the SLSD may be a useful tool for identifying runners with poor running mechanics when 2- or 3-dimensional gait analysis is not available. However, the associations between SLSD performance and running kinetics, as well as the influences of sex and muscle strength on these relationships, remain unclear.ObjectiveTo evaluate whether kinematics on the SLSD predict kinematics and kinetics while running and whether the relationships differ between men and women and are mediated by muscle strength.DesignCross-sectional study.SettingBiomechanics research laboratory.Patients or Other ParticipantsFifty highly trained runners (25 men, 25 women; age = 27.8 ± 9.2 years, height = 1.69 ± 0.26 m, mass = 66.3 ± 15.0 kg, running distance = 45.2 ± 19.1 mile/wk [72.32 ± 30.56 km/wk]).Main Outcome Measure(s)Relationships between kinematics on the SLSD and kinematics and kinetics during running were evaluated. We also assessed whether muscle strength moderated these relationships.ResultsFor men, linear regression revealed that peak hip adduction (R² = 0.306, P = .012), internal rotation (R² = 0.439, P = .002), knee valgus (R² = 0.544, P = .001), and rearfoot eversion (R² = 0.274, P = .008) on the SLSD were strongly predictive of kinematics during running. In women, only peak hip internal rotation (R² = 0.573, P = .001), knee valgus (R² = 0.442, P = .001), and rearfoot eversion (R² = 0.384, P = .012) predicted running kinematics. In women, total medial collapse on the SLSD predicted peak hip-adductor moment (R² = 0.364, P = .001) during running. None of the relationships were moderated by muscle strength in either men or women.ConclusionsKinematics during the SLSD predicted kinematics while running in both men and women but only predicted kinetics while running in women. Given that none of the relationships between SLSD performance and running mechanics were moderated by muscle strength, clinicians should assess movement quality and strength independently.     

Validation of Foot-Strike Assessment Using Wearable Sensors During Running

Wearable sensors are capable of capturing foot-strike positioning, which lends insight into landing biomechanics during running. The purpose of our study was to assess the relationship between foot-strike categorization and foot-strike angle during running to validate the sensor-derived foot-strike outcome. Twenty collegiate cross-country athletes (12 females, 8 males) ran at 2 speeds on an instrumented treadmill. RunScribe sensors were used to determine foot-strike categorizations (1–5 = rearfoot, 6–10 = midfoot, 11–16 = forefoot), and foot-strike angles were simultaneously assessed with 3-dimensional motion capture bilaterally. We calculated Pearson r correlation coefficients to compare foot-strike categorizations and angles at initial contact over 800 steps as well as sensor foot-strike identification accuracy. A strong, inverse correlation between foot-strike categorizations and foot-strike angles was present (r = −0.86, P < .001). Overall, the sensors demonstrated 78% accuracy (rearfoot = 72.5%, midfoot = 55.3%, forefoot = 95.4%). These results support the concurrent validity of the sensor-derived foot-strike measures.     

Knee biomechanical factors associated with patellofemoral pain in recreational runners

BackgroundPatellofemoral pain (PFP) is a common injury among runners. Knee biomechanical factors associated with PFP, however, remain unclear. The purpose of this study was to determine possible associations between knee biomechanics and symptoms of PFP in recreational runners.MethodsFifteen male and 15 female recreational runners with PFP were enrolled as the PFP group, 30 matched runners without PFP were recruited as the control group. The PFP group was tested running with and without knee pain, while the control group had only one running test. Reflective marker coordinates and ground reaction force data were collected in each test. Knee kinematics and kinetics during running were reduced and compared between groups (PFP group without knee pain and control group) and between pain conditions (PFP group with knee pain and without knee pain), as well as between sexes.ResultsFemale and male participants with PFP had an increased peak knee valgus angle when running without pain compared to matched controls (P = 0.001), and to themselves when running with pain (P = 0.001). Male participants with PFP also had an increased peak knee flexion angle when running without pain compared to matched controls (P = 0.008), however did not decrease their peak knee flexion angle when running with pain (P = 0.245). No significant main effect of group or pain condition on any peak knee joint moment during running was detected (P ≥ 0.175).ConclusionsIncreased peak knee valgus angle during running appears to be a critical biomechanical factor associated with PFP in recreational runners, while decreasing knee valgus angle during running may be an adaptation to reduce symptoms of PFP. Increased peak knee flexion angle during running appears to be another biomechanical factor associated with PFP that is sex specific for male recreational runners.     

Fatigue-Induced Hip-Abductor Weakness and Changes in Biomechanical Risk Factors for Running-Related Injuries

ContextDespite overlap between hip-abductor (HABD) weakness and fatigue-induced changes in running, the interaction of these theorized contributors to running injuries has been underevaluated.ObjectiveTo assess the effects of a fatiguing run on HABD torque and evaluate the correlation between HABD torque and previously identified running-related injury pathomechanics while participants were rested or fatigued.DesignCrossover study.SettingLaboratory.Patients or Other ParticipantsA total of 38 healthy, physically active males (age = 21.61 ± 4.02 years, height = 1.78 ± 0.08 m, body mass = 76.00 ± 12.39 kg).Intervention(s)Data collection consisted of rested-state collection, a fatiguing treadmill-run protocol, and fatigued-state collection. For the HABD measures, side-lying handheld-dynamometer isometric tests were performed and converted to torque using femur length. For the gait analysis, kinematic (240 Hz) and kinetic (960 Hz) running (4.0 m/s) data were collected for 3 trials. The fatigue protocol involved a graded exercise test and 80% o₂max run to exhaustion. Immediately after the run, fatigued-state measures were obtained.Main Outcome Measure(s)Variables of interest were HABD torque and peak angles, velocities, and moments for hip and knee adduction and internal rotation. Differences between conditions were compared using paired t tests. Pearson correlation coefficients were calculated to evaluate relationships between HABD torque and biomechanical variables.ResultsFatigue decreased HABD torque and increased hip-adduction angle, knee-adduction velocity, and hip and knee internal-rotation velocities and moments (all P values < .05). In the rested state, HABD torque was correlated with hip-adduction velocity (r = –0.322, P = .049). In the fatigued state, HABD torque was correlated with hip-adduction velocity (r = –0.393, P = .015), hip internal-rotation velocity (r = –0.410, P = .01), and knee-adduction angle (r = 0.385, P = .017) and velocity (r = −0.378, P = .019).ConclusionsChanges in joint velocities due to fatigue and correlations between HABD torque and hip- and knee-joint velocities highlight the need to consider not only the quantity of HABD strength but also the rate of eccentric control of HABDs.     

Gait Biomechanics in Individuals Meeting Sufficient Quadriceps Strength Cutoffs After Anterior Cruciate Ligament Reconstruction

ContextQuadriceps weakness is associated with disability and aberrant gait biomechanics after anterior cruciate ligament reconstruction (ACLR). Strength-sufficiency cutoff scores, which normalize quadriceps strength to the mass of an individual, can predict who will report better function after ACLR. However, whether gait biomechanics differ between individuals who meet a strength-sufficiency cutoff (strong) and those who do not (weak) remains unknown.ObjectiveTo determine whether vertical ground reaction force, knee-flexion angle, and internal knee-extension moment differ throughout the stance phase of walking between individuals with strong and those with weak quadriceps after ACLR.DesignCase-control study.SettingLaboratory.Patients or Other ParticipantsIndividuals who underwent unilateral ACLR >12 months before testing were dichotomized into strong (n = 31) and weak (n = 116) groups.Main Outcome MeasuresMaximal isometric quadriceps strength was measured at 90° of knee flexion using an isokinetic dynamometer and normalized to body mass. Individuals who demonstrated maximal isometric quadriceps strength ≥3.0 N·m·kg⁻¹ were considered strong. Three-dimensional gait biomechanics were collected at a self-selected walking speed. Biomechanical data were time normalized to 100% of stance phase. Vertical ground reaction force was normalized to body weight (BW), and knee-extension moment was normalized to BW × height. Pairwise comparison functions were calculated for each outcome to identify between-groups differences for each percentile of stance.ResultsVertical ground reaction force was greater in the weak group for the first 22% of stance (peak mean difference [MD] = 6.2% BW) and less in the weak group between 36% and 43% of stance (MD = 1.4% BW). Knee-flexion angle was greater (ie, more flexion) in the strong group between 6% and 52% of stance (MD = 2.3°) and smaller (ie, less flexion) between 68% and 79% of stance (MD = 1.0°). Knee-extension moment was greater in the strong group between 7% and 62% of stance (MD = 0.007 BW × height).ConclusionsIndividuals with ACLR who generated knee-extension torque ≥3.0 N·m·kg⁻¹ exhibited different biomechanical gait profiles than those who could not. More strength may allow for better energy attenuation after ACLR.     

Glenohumeral rotational motion and strength and baseball pitching biomechanics

Context:

Addressing loss of shoulder range of motion and rotator cuff weakness in injury-prevention programs might be an effective strategy for preventing throwing arm injuries in baseball pitchers. However, the influence of these clinical measures on pitching biomechanics is unclear.

Objective:

To evaluate the relationships among clinical measures of shoulder rotational motion and strength and 3-dimensional pitching biomechanics and to evaluate the presence of coupling between the shoulder and the elbow during pitching to provide insight into the influence of clinical shoulder characteristics on elbow biomechanics.

Design:

Cross-sectional study.

Setting:

Biomechanics laboratory.

Patients or Other Participants:

A total of 27 uninjured male high school baseball pitchers (age  =  16 ± 1.1 years, height  =  183 ± 7 cm, mass  =  83 ± 12 kg).

Main Outcome Measure(s):

Clinical measures included shoulder internal- and external-rotation range of motion and peak isometric internal- and external-rotator strength. Three-dimensional upper extremity biomechanics were assessed as participants threw from an indoor pitching mound to a target at regulation distance. Linear regressions were used to assess the influence of clinical measures on the peak shoulder internal and external rotation moments and the peak elbow-adduction moment.

Results:

We found a positive relationship between clinically measured internal-rotator strength and shoulder external-rotation moment (R²  =  0.181, P  =  .04) during pitching. We also noted an inverse relationship between clinically measured external-rotation motion and the elbow-adduction moment (R²  =  0.160, P  =  .04) and shoulder internal-rotation moment (R²  =  0.250, P  =  .008) during pitching. We found a positive relationship between peak shoulder internal-rotation moment and the peak elbow-adduction moment (R²  =  0.815, P < .001) during pitching.

Conclusions:

This study provides insight into the effects of shoulder strength and motion on pitching biomechanics and how these clinical measures might contribute to throwing arm injuries in the baseball pitcher. A relationship also was identified between peak shoulder and elbow moments in the throwing arm during pitching, providing biomechanical support for addressing clinical shoulder characteristics as a potential strategy for preventing elbow injury.     

Sport Specialization in Middle School and High School Long-Distance Runners

ContextPrevious reports suggested that highly specialized adolescent athletes may be at a higher risk of injury, worse sleep quality, and less sport enjoyment than low-level specialized athletes. To date, the sport specialization literature has primarily addressed adolescent athletes in a variety of sports. However, whether the findings on sport specialization in predominantly nonrunning athletes are generalizable to adolescent long-distance runners is unknown.ObjectiveTo compare injury history, running volume, quality of life, sleep habits, and running enjoyment among male and female middle school and high school long-distance runners at different sport specialization levels.DesignCross-sectional study.SettingOnline survey.Patients or Other ParticipantsA total of 102 male (age = 15.8 ± 0.9 years) and 156 female (age = 15.6 ± 1.4 years) uninjured middle school and high school athletes who participated in long-distance running activities (completion rate = 50.7%).Main Outcome Measure(s)Participants were stratified by sex and sport specialization level (low, moderate, or high). Group differences were assessed in self-reported running-related injuries, running habits, EQ-5D-Y quality of life, Pittsburgh Sleep Quality Index sleep quality, sleep duration, and running enjoyment.ResultsHighly specialized male and female middle school and high school long-distance runners reported more months of competition per year (P < .001), higher weekly run distance (P < .001), more runs per week (P < .001), higher average distance per run (P < .001), and greater running enjoyment (P < .001) than low-level specialized runners. Adolescent boys reported a higher average weekly run distance (P = .01), higher average distance per run (P = .01), and better sleep quality (P = .01) than adolescent girls. No differences among sport specialization levels were found for running-related injuries (P = .25), quality of life (P = .07), sleep quality (P = .19), or sleep duration (P = .11) among male or female middle school and high school runners.ConclusionsHighly specialized male and female middle school and high school long-distance runners reported higher running volumes and running enjoyment than low-level specialized runners. However, high-level specialized runners did not describe a greater number of running-related injuries, lower quality of life, or lower sleep quality or duration as expected.     

Influence of Prolonged Running and Training on Tibial Acceleration and Movement Quality in Novice Runners

ContextChanges in lower limb loading and movement quality after prolonged running and training periods might influence injury risks in runners.ObjectivesTo assess (1) the effects of a single prolonged run and a 3-week running training program on peak tibial acceleration (PTA) during running and Functional Movement Screen (FMS) criterion tests, and (2) the relationship between running volume during the 3-week training program and changes in PTA and FMS scores after training.DesignCase series.SettingResearch laboratory.Patients or Other ParticipantsTen novice runners (age = 27 ± 7 years) with 15 ± 14 months of running experience, who ran on average 19.6 ± 4.8 km per week at a preferred pace of 7:05 ± 1:30 minutes per km.Main Outcome Measure(s)Participants completed a 30-minute submaximal prolonged treadmill run and 3-week training program with 25% increases in weekly running volume. Peak tibial acceleration and the deep-squat and active straight-leg–raise criterion FMS test scores were assessed before and after the prolonged run at enrollment and after the training program (ie, 3 testing sessions).ResultsNo differences in PTA or FMS scores were observed among the 3 testing times. Although the changes in PTA (r = 0.57) and FMS aggregate score (r = 0.15) were not significantly correlated with training volume, training volume explained 32% of the variance in the PTA change from before to after training.ConclusionsOur findings suggest that tibial acceleration and movement quality were not influenced by a single submaximal-effort prolonged run or a 3-week training period. However, novice runners who have a greater increase in running volume might be more susceptible to training-related changes in tibial acceleration than those whose running volume is less.     

Increased Contact Time and Strength Deficits in Runners With Exercise-Related Lower Leg Pain

ContextExercise-related lower leg pain (ERLLP) is common in runners.ObjectiveTo compare biomechanical (kinematic, kinetic, and spatiotemporal) measures obtained from wearable sensors as well as lower extremity alignment, range of motion, and strength during running between runners with and those without ERLLP.DesignCase-control study.SettingField and laboratory.Patients or Other ParticipantsOf 32 young adults who had been running regularly (>10 mi [16 km] per week) for ≥3 months, 16 had ERLLP for ≥2 weeks and 16 were healthy control participants.Main Outcome Measure(s)Both field and laboratory measures were collected at the initial visit. The laboratory measures consisted of alignment (arch height index, foot posture index, navicular drop, tibial torsion, Q-angle, and hip anteversion), range of motion (great toe, ankle, knee, and hip), and strength. Participants then completed a 1.67-mi (2.69-km) run along a predetermined route to calibrate the RunScribe devices. The RunScribe wearable sensors collected kinematic (pronation excursion and maximum pronation velocity), kinetic (impact g and braking g), and spatiotemporal (stride length, step length, contact time, stride pace, and flight ratio) measures. Participants then wore the sensors during at least 3 training runs in the next week.ResultsThe ERLLP group had a slower stride pace than the healthy group, which was accounted for as a covariate in subsequent analyses. The ERLLP group had a longer contact time during the stance phase of running (mean difference [MD] = 18.00 ± 8.27 milliseconds) and decreased stride length (MD = −0.11 ± 0.05 m) than the control group. For the clinical measures, the ERLLP group demonstrated increased range of motion for great-toe flexion (MD = 13.9 ± 4.6°) and ankle eversion (MD = 6.3 ± 2.7°) and decreased strength for ankle inversion (MD = −0.49 ± 0.23 N/kg), ankle eversion (MD = −0.57 ± 0.27 N/kg), and hip flexion (MD = −0.99 ± 0.39 N/kg).ConclusionsThe ERLLP group exhibited a longer contact time and decreased stride length during running as well as strength deficits at the ankle and hip. Gait retraining and lower extremity strengthening may be warranted as clinical interventions in runners with ERLLP.     

髌股关节痛业余跑者性别特异的下肢生物力学特征

目的 研究髌股关节痛（patellofemoral pain,PFP）业余跑者性别特异的下肢生物力学特征。方法 选取15名男性和10名女性PFP业余跑者作为实验组,并匹配25名无损伤业余跑者作为对照组。采集所有受试者跑步时的下肢运动学、动力学和表面肌电数据。采用双因素方差分析确定组别与性别对跑步时下肢生物力学特征的影响。结果 男性PFP业余跑者跑步缓冲期最大膝屈角度显著大于对照组;男性和女性PFP业余跑者跑步缓冲期最大髋内收角度显著大于对照组,且女性显著大于男性。结论 不同性别PFP业余跑者在跑步时表现出不同的下肢生物力学特征,PFP临床治疗应具有性别特异性。     

Weight-Bearing Versus Traditional Strength Assessments of the Hip Musculature

ContextTraditional nonweight-bearing (NWB) hip-strength assessments may not directly translate to functional strength during weight-bearing (WB) activity. How NWB assessments of hip muscle strength compare with WB assessments in various positions is currently unknown.ObjectiveTo determine the magnitude of the differences and correlations between NWB hip strength and WB functional strength during the squatting and lunge (LNG) positions in female athletes.DesignCrossover design.SettingLaboratory.Patients or Other ParticipantsFemale athletes (N = 51, age = 16.2 ± 3.5 years, height = 161.5 ± 8.3 cm, mass = 58.3 ± 11.6 kg).Intervention(s)Isometric resistance (N/kg) was determined for the dominant and nondominant limbs via WB assessments (squat-bilateral [legs tested simultaneously], squat-unilateral, and lunge positions) and NWB assessments (hip external rotation [HER], hip extension [HEXT], and hip abduction [HAB]).Main Outcome Measure(s)To compare differences between positions (P ≤ .05), we used effect sizes (d) and matched-pairs t tests, and we calculated Pearson r and R² values.ResultsDuring the squat-bilateral on the dominant limb, females produced the most hip torque (6.13 ± 1.12 N/kg). The magnitudes of differences were very large compared with HER (3.96 ± 0.83, d = 2.2), HEXT (3.22 ± 0.69, d = 3.2), and HAB (3.80 ± 1.01, d = 2.2; all P values ≤ .01), and positions were moderately correlated (r = 0.347–0.419, R² = 0.12–0.18). The lunge position produced the least amount of torque in the dominant limb (2.44 ± 0.48 N/kg) compared with HER (d = −2.3), HEXT (d = −1.3), and HAB (d = −1.7; all P values ≤ .001), and correlations were small to moderate (r = 0.236–0.310, R² = 0.06–0.10).ConclusionsStrength in WB positions was different than strength evaluated using traditional NWB assessments in female athletes. Weight-bearing tests may provide clinicians with additional information regarding strength and function.     

Metabolic Response to Submaximal and Maximal Exercise in People with Severe Obesity,Prediabetes, and Diabetes

IntroductionMetabolic adaptations to maximal physical exercise in people with obesity (PwO) are scarcely described. This cross-sectional study evaluates the metabolic response to exercise via the respiratory exchange ratio (RER) in PwO and different degrees of glycemic control.MethodsEighty-five PwO (body mass index 46.0 [39.0–54.0] kg/m²), that is, 32 normoglycemic (Ob-N), 25 prediabetic (Ob-preDM), and 28 diabetic (Ob-T2DM) subjects and 18 healthy subjects performed an incremental, maximal cardiopulmonary exercise test. The RER was measured at rest (RERrest) and at peak exercise (RERpeak).ResultsRERpeak was significantly higher in healthy subjects than that in PwO. Among those, RERpeak was significantly higher in Ob-N than that in Ob-preDM and Ob-T2DM (1.20 [1.15–1.27] vs. 1.18 [1.10–1.22] p = 0.04 and vs. 1.14 [1.10–1.18] p < 0.001, respectively). Accordingly, ΔRER (RERpeak-RERrest) was lower in Ob-preDM and Ob-T2DM than that in Ob-N (0.32 [0.26–0.39] p = 0.04 and 0.29 [0.24–0.36] p < 0.001 vs. 0.38 [0.32–0.43], respectively), while no significant difference was found in ΔRER between Ob-preDM and Ob-T2DM and not even between Ob-N and healthy subjects. Moreover, ΔRER in PwO correlated with glucose area under curve (p = 0.002).ConclusionsPwO demonstrate restricted metabolic response during maximal exercise. Particularly, those with prediabetes already show metabolic inflexibility during exercise, similarly to those with type 2 diabetes. These findings also suggest a potential role of cardiopulmonary exercise testing in detecting early metabolic alterations in PwO.     

Lean Mass Loss and Altered Muscular Aerobic Capacity after Bariatric Surgery

IntroductionPatients undergoing weight loss surgery do not improve their aerobic capacity or peak oxygen uptake (VO₂peak) after bariatric surgery and some still complain about asthenia and/or breathlessness. We investigated the hypothesis that a post-surgery muscular limitation could impact the ventilatory response to exercise by evaluating the post-surgery changes in muscle mass, strength, and muscular aerobic capacity, measured by the first ventilatory threshold (VT).MethodsThirteen patients with obesity were referred to our university exercise laboratory before and 6 months after bariatric surgery and were matched by sex, age, and height to healthy subjects with normal weight. All subjects underwent a clinical examination, blood sampling, and body composition assessment by dual-energy X-ray absorptiometry, respiratory and limb muscle strength assessments, and cardiopulmonary exercise testing on a cyclo-ergometer.ResultsBariatric surgery resulted in a loss of 34% fat mass, 43% visceral adipose tissue, and 12% lean mass (LM) (p < 0.001). Absolute handgrip, quadriceps, or respiratory muscle strength remained unaffected, while quadriceps/handgrip strength relative to LM increased (p < 0.05). Absolute VO₂peak or VO₂peak/LM did not improve and the first VT was decreased after surgery (1.4 ± 0.3 vs. 1.1 ± 0.4 L min⁻¹, p < 0.05) and correlated to the exercising LM (LM legs) (R = 0.84, p < 0.001).ConclusionsAlthough bariatric surgery has numerous beneficial effects, absolute VO₂peak does not improve and the weight loss-induced LM reduction is associated to an altered muscular aerobic capacity, as reflected by an early VT triggering early exercise hyperventilation.     

Lower extremity muscle activation and knee flexion during a jump-landing task

Context

Decreased sagittal-plane motion at the knee during dynamic tasks has been reported to increase impact forces during landing, potentially leading to knee injuries such as anterior cruciate ligament rupture.

Objective

To describe the relationship between lower extremity muscle activity and knee-flexion angle during a jump-landing task.

Design

Cross-sectional study.

Setting

Research laboratory.

Patients or Other Participants

Thirty recreationally active volunteers (15 men, 15 women: age = 21.63 ± 2.01 years, height = 173.95 ± 11.88 cm, mass = 72.57 ± 14.25 kg).

Intervention(s)

Knee-flexion angle and lower extremity muscle activity were collected during 10 trials of a jump-landing task.

Main Outcome Measure(s)

Simple correlation analyses were performed to determine the relationship between each knee-flexion variable (initial contact, peak, and displacement) and electromyographic amplitude of the gluteus maximus (GMAX), quadriceps (VMO and VL), hamstrings, gastrocnemius, and quadriceps : hamstring (Q : H) ratio. Separate forward stepwise multiple regressions were conducted to determine which combination of muscle activity variables predicted each knee-flexion variable.

Results

During preactivation, VMO and GMAX activity and the Q : H ratio were negatively correlated with knee-flexion angle at initial contact (VMO: r = −0.382, P = .045; GMAX: r = −0.385, P = .043; Q : H ratio: r = −0.442, P = .018). The VMO, VL, and GMAX deceleration values were negatively correlated with peak knee-flexion angle (VMO: r = −0.687, P = .001; VL: r = −0.467, P = .011; GMAX: r = −0.386, P = .043). The VMO and VL deceleration values were negatively correlated with knee-flexion displacement (VMO: r = −0.631, P = .001; VL: r = −0.453, P = .014). The Q : H ratio and GM activity predicted 34.7% of the variance in knee-flexion angle at initial contact (P = .006). The VMO activity predicted 47.1% of the variance in peak knee-flexion angle (P = .001). The VMO and VL activity predicted 49.5% of the variance in knee-flexion displacement (P = .001).

Conclusions

Greater quadriceps and GMAX activation and less hamstrings and gastrocnemius activation were correlated with smaller knee-flexion angles. This landing strategy may predispose an individual to increased impact forces due to the negative influence on knee-flexion position.Key Words: knee injuries, anterior cruciate ligament, biomechanics

Key Points

• Small knee-flexion angles were largely influenced by high quadriceps:hamstrings (Q:H) co-activation ratios during the preparatory phase.
• The high Q:H co-activation ratios were largely the result of diminished hamstrings activity rather than excessive quadriceps activity.
• Interventions designed to enhance preparatory hamstrings activity may be helpful in balancing Q:H co-activation ratios and placing the knee in a more flexed position at initial contact, which may reduce anterior cruciate loading and injury risk.

Sports medicine researchers have extensively examined lower extremity mechanics during athletic movements with the goal of identifying factors that could lead to subsequent knee injuries. Much of the recent literature on knee injuries has focused specifically on determining the lower extremity movement patterns that could predispose an individual to noncontact anterior cruciate ligament (ACL) injury. Analyses of videos recorded during noncontact ACL injury events have repeatedly shown the body to be in an erect posture (ie, decreased knee, hip, and trunk flexion), which implicates decreased sagittal-plane motion as a potential risk factor for ACL injury.^1–3An increasing amount of evidence suggests that decreased sagittal-plane motion at the knee during jumping, landing, and cutting may contribute to ACL injuries from the influence of knee-flexion angle on impact forces.^4–7 Greater ground reaction forces⁶ and proximal anterior tibial shear force^4,5,7 are present when individuals land with a more extended knee compared with a more flexed knee. These findings suggest that knee-flexion angle may influence ACL injury risk by modifying the magnitude of ACL loading. Although decreased knee-flexion angles have been found to influence impact forces, researchers have yet to determine which neuromuscular characteristics influence knee-flexion angle during landing tasks. This information could improve our understanding of ACL injury mechanisms.Activation of the muscles controlling sagittal-plane motion at the knee and hip is likely to influence the amount of knee flexion that occurs during dynamic tasks such as a jump landing. Greater concentric action of the hamstrings and gastrocnemius muscles may result in larger internal knee-flexion moments and position the knee in more flexion during landing. Conversely, greater eccentric action of the quadriceps and gluteus maximus muscles may create larger internal knee- and hip-extension moments, respectively, and facilitate a more erect body posture (less knee and hip flexion).^7–9 The relative activation between agonist and antagonist muscles may also be a factor influencing knee-flexion position.^10,11 Therefore, quadriceps to hamstrings co-activation (Q:H ratio) may be important because these are the primary muscles controlling the net internal knee flexion-extension moment.Investigators have not yet studied the association between the activation of sagittal-plane muscles and knee-flexion position during a jump-landing task. Therefore, the purpose of our study was to evaluate relationships between lower extremity muscle activity (quadriceps, hamstrings, gluteus maximus, gastrocnemius, and Q:H ratio) and knee-flexion angle during a jump-landing task. We hypothesized that the relationships between quadriceps and gluteus maximus electromyographic (EMG) amplitude and Q:H ratio and knee-flexion angle during a jump-landing task would be negative. Additionally, we hypothesized that the relationship between hamstrings and gastrocnemius EMG amplitude and knee-flexion angle during a jump-landing task would be positive.     

Age- and Sex-Based Differences in Exertional Heat Stroke Incidence in a 7-Mile Road Race

ContextSex, age, and wet-bulb globe temperature (WBGT) have been proposed risk factors for exertional heat stroke (EHS) despite conflicting laboratory and epidemiologic evidence.ObjectiveTo examine differences in EHS incidence while accounting for sex, age, and environmental conditions.DesignObservational study.SettingFalmouth Road Race, a warm-weather 7-mi (11.26-km) running road race.Patients or Other ParticipantsWe reviewed records from patients treated for EHS at medical tents.Main Outcome Measure(s)The relative risk (RR) of EHS between sexes and across ages was assessed with males as the reference population. Multivariate linear regression analyses were calculated to determine the relative contribution of sex, age, and WBGT to the incidence of EHS.ResultsAmong 343 EHS cases, the female risk of EHS was lower overall (RR = 0.71; 95% confidence interval [CI] = 0.58, 0.89; P = .002) and for age groups 40 to 49 years (RR = 0.43; 95% CI = 0.24, 0.77; P = .005) and 50 to 59 years (RR = 0.31; 95% CI = 0.13, 0.72; P = .005). The incidence of EHS did not differ between sexes in relation to WBGT (P > .05). When sex, age, and WBGT were considered in combination, only age groups <14 years (β = 2.41, P = .008), 15 to 18 years (β = 3.83, P < .001), and 19 to 39 years (β = 2.24, P = .014) significantly accounted for the variance in the incidence of EHS (R² = .10, P = .006).ConclusionsIn this unique investigation of EHS incidence in a road race, we found a 29% decreased EHS risk in females compared with males. However, when sex was considered with age and WBGT, only younger age accounted for an increased incidence of EHS. These results suggest that road race medical organizers should consider participant demographics when organizing the personnel and resources needed to treat patients with EHS. Specifically, organizers of events with greater numbers of young runners (aged 19 to 39 years) and males should prioritize ensuring that medical personnel are adequately prepared to handle patients with EHS.     

Effect of exercise training on Ca2+ release units of left ventricular myocytes of spontaneously hypertensive rats

In cardiomyocytes, calcium (Ca²⁺) release units comprise clusters of intracellular Ca²⁺ release channels located on the sarcoplasmic reticulum, and hypertension is well established as a cause of defects in calcium release unit function. Our objective was to determine whether endurance exercise training could attenuate the deleterious effects of hypertension on calcium release unit components and Ca²⁺ sparks in left ventricular myocytes of spontaneously hypertensive rats. Male Wistar and spontaneously hypertensive rats (4 months of age) were divided into 4 groups: normotensive (NC) and hypertensive control (HC), and normotensive (NT) and hypertensive trained (HT) animals (7 rats per group). NC and HC rats were submitted to a low-intensity treadmill running protocol (5 days/week, 1 h/day, 0% grade, and 50-60% of maximal running speed) for 8 weeks. Gene expression of the ryanodine receptor type 2 (RyR2) and FK506 binding protein (FKBP12.6) increased (270%) and decreased (88%), respectively, in HC compared to NC rats. Endurance exercise training reversed these changes by reducing RyR2 (230%) and normalizing FKBP12.6 gene expression (112%). Hypertension also increased the frequency of Ca²⁺ sparks (HC=7.61±0.26 vs NC=4.79±0.19 per 100 µm/s) and decreased its amplitude (HC=0.260±0.08 vs NC=0.324±0.10 ΔF/F₀), full width at half-maximum amplitude (HC=1.05±0.08 vs NC=1.26±0.01 µm), total duration (HC=11.51±0.12 vs NC=14.97±0.24 ms), time to peak (HC=4.84±0.06 vs NC=6.31±0.14 ms), and time constant of decay (HC=8.68±0.12 vs NC=10.21±0.22 ms). These changes were partially reversed in HT rats (frequency of Ca²⁺ sparks=6.26±0.19 µm/s, amplitude=0.282±0.10 ΔF/F₀, full width at half-maximum amplitude=1.14±0.01 µm, total duration=13.34±0.17 ms, time to peak=5.43±0.08 ms, and time constant of decay=9.43±0.15 ms). Endurance exercise training attenuated the deleterious effects of hypertension on calcium release units of left ventricular myocytes.     

Influence of home-based telemonitored Nordic walking training on autonomic nervous system balance in heart failure patients

Introduction

Rehabilitation positively affects the modulation of the autonomic nervous system (ANS). There are no papers evaluating the influence of Nordic walking training (NW) on ANS activity among chronic heart failure (CHF) patients. The aim of study was to assess the influence of NW on ANS activity measured by heart rate variability (HRV) and heart rate turbulence (HRT) in CHF patients and its correlation with physical capacity improvement measured by peak oxygen consumption (peak VO₂ [ml/kg/min]) in the cardiopulmonary exercise treadmill test (CPET).

Material and methods

The study group comprised 111 CHF patients (NYHA class II–III; ejection fraction (EF) ≤ 40%). Patients were randomized (2 : 1) to 8-week NW (five times weekly) at 40–70% of maximal heart rate (training group – TG) (n = 77), or to a control group (CG) (n = 34). The effectiveness of NW was assessed by changes (delta (Δ)) in peak VO₂, HRV and HRT as a result of comparing these parameters from the beginning and the end of the programme.

Results

Eventually, 36 TG patients and 15 CG patients were eligible for HRV and HRT analysis. In the TG low/high frequency ratio (LF/HF) decreased (1.9 ±1.11 vs. 1.7 ±0.63, p = 0.0001) and peak VO₂ increased (16.98 ±4.02 vs. 19.70 ±4.36 ml/kg/min, p < 0.0001). Favourable results in CG were not observed. The differences between TG and CG were significant: Δpeak VO₂ (p = 0.0081); ΔLF/HF (p = 0.0038). An inverse correlation was found between the decrease in ΔLF/HF and the increase in Δpeak VO₂ (R = –0.3830, p = 0.0211) only in the TG. Heart rate variability did not change significantly in either group.

Conclusions

Nordic walking positively affects the parasympathetic-sympathetic balance in CHF patients, which correlates with the improvement in Δpeak VO₂. No significant influence of NW on HRT was observed.     

Hamstrings Stiffness and Landing Biomechanics Linked to Anterior Cruciate Ligament Loading

Context:

Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks.

Objective:

To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury.

Design:

Cross-sectional study.

Setting:

Research laboratory.

Patients or Other Participants:

A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg).

Intervention(s):

Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests.

Main Outcome Measure(s):

Hamstrings stiffness was normalized to body mass (N/m·kg⁻¹). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height.

Results:

Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t₂₂ = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t₂₂ = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t₂₂ range = 1.729–2.224, P < .05).

Conclusions:

Greater hamstrings stiffness was associated with landing biomechanics consistent with less ACL loading and injury risk. Musculotendinous stiffness is a modifiable characteristic; thus exercises that enhance hamstrings stiffness may be important additions to ACL injury-prevention programs.Key Words: viscoelastic, musculotendinous, valgus, anterior tibial shear force

Key Points

• Individuals with greater hamstrings stiffness displayed more favorable landing biomechanics for anterior cruciate ligament (ACL) loading and injury risk than individuals with less hamstrings stiffness as evidenced by smaller frontal-plane knee moments and a more-flexed knee at the instants of critical biomechanical knee events.
• Greater hamstrings stiffness was associated with smaller anterior tibial shear forces.
• A high level of hamstrings stiffness may limit ACL injury risk by limiting frontal- and sagittal-plane ACL-loading mechanisms.

Anterior cruciate ligament (ACL) injury commonly occurs during landing,¹ and researchers have suggested that a landing biomechanics profile consisting of large ground reaction forces, anterior tibial shear force, knee-valgus angle, and external knee-flexion and -valgus moments increases ACL loading.^2–4 A more-extended knee during landing exacerbates this profile, whereas a more-flexed knee decreases these variables,^4–6 likely limiting ACL loading and injury risk. For example, Blackburn and Padua⁵ demonstrated that increasing knee-flexion angle during landing reduced ground reaction forces. Similarly, Pollard et al⁶ categorized participants into high- and low-flexion groups based on performance of a landing task and reported smaller knee-valgus angles and moments in the high-flexion group.Stiffness quantifies the resistance of the musculotendinous unit to lengthening, and hamstrings stiffness may have important implications for ACL loading and injury risk. Greater hamstrings stiffness is associated with greater function in ACL-deficient individuals.⁷ During controlled perturbations, healthy individuals with greater hamstrings stiffness also display less anterior tibial translation, which is an arthrokinematic motion that directly loads the ACL.⁸ Given that anterior tibial translation results from anterior tibial shear force, greater hamstrings stiffness seemingly would resist anterior tibial shear force during landing more effectively than less hamstrings stiffness. Greater hamstrings stiffness also is correlated with less hamstrings flexibility.⁹ This heightened resistance to knee extension may lead to a more flexed knee during landing, producing more favorable landing biomechanics for ACL loading and injury risk. This notion is supported by Boden et al,¹ who reported that participants with ACL injuries displayed greater hamstrings flexibility than an uninjured cohort, suggesting that “above-average” hamstrings flexibility and, therefore, less hamstrings stiffness may increase ACL injury risk.Musculotendinous stiffness is a modifiable neuromuscular property^10,11 that could be targeted in ACL injury-prevention programs. Whereas greater hamstrings stiffness appears to limit ACL loading during controlled perturbations,⁸ it is unclear how hamstrings stiffness influences biomechanical ACL-loading mechanisms during dynamic tasks in which ACL injury commonly occurs. Therefore, the purpose of our investigation was to evaluate the influence of hamstrings musculotendinous stiffness on lower extremity kinematics and kinetics during landing. We hypothesized that individuals with greater hamstrings stiffness would display greater knee flexion during landing, resulting in smaller peak ground reaction forces, anterior tibial shear forces, internal knee-extension and -varus moments (ie, the internal/muscular responses to external moments), and knee-valgus angles. We also hypothesized that individuals with greater hamstrings stiffness would display greater knee-flexion angles at the instants of peak kinetics.