The effect of foot-stretcher position and stroke rate on ergometer rowing kinematics.

Rowing ergometers are popular tools for general fitness and competitive crew teams. The effect of the equipment set up on the rowing stroke has received limited attention. This study aimed to determine the effects of altering the foot-stretcher position on rowing kinematics across different stroke rates. Eleven college-level rowers took part in this study. A rowing ergometer was modified to allow the height and angle of the foot-stretcher to be adjusted. Seven foot-stretcher positions were tested, each at rates of 22, 26, and 32 strokes per minute. Sagittal plane kinematic waveforms were compared between conditions for all major joints using statistical parametric mapping, and temporal variables were assessed (p < 0.05). Stroke rate was found to affect kinematic patterns for all joints. The effect of the foot-stretcher position was limited to the ankle and hip. Similarly, the timing of events during the rowing stroke was affected by the stroke rate, but not foot position. These results indicate that while some limited changes to the stroke technique can be caused by altering the foot-stretcher position, the changes were largely compensated for by the rowers and are generally smaller than differences between stroke rates.

Game-Day Pitch and Throw Count Feasibility Using a Single Sensor to Quantify Workload in Youth Baseball Players.

Background: Pitch count recommendations are used to reduce injury risk in youth baseball pitchers and are based chiefly on expert opinion, with limited scientific support. Furthermore, they only account for pitches thrown against a hitter and do not include the total number of throws on the day a player pitched. Currently, counts are recorded manually. Purpose: To provide a method using a wearable sensor to quantify total throws per game that is compliant with Little League Baseball rules and regulations. Study Design: Descriptive laboratory study. Methods: Eleven male baseball players (age, 10-11 years) from an 11U (players 11 years and younger) competitive travel team were evaluated over a single summer season. An inertial sensor was placed above the midhumerus of the throwing arm and was worn during baseball games across the season. A throw identification algorithm capturing all throws and reporting linear acceleration and peak linear acceleration was used to quantify throwing intensity. Pitching charts were collected and used to verify actual pitches thrown against a hitter in a game versus all other throws identified. Results: A total of 2748 pitches and 13,429 throws were captured. On the day a player pitched, he averaged 36 ± 18 pitches (23%) and 158 ± 106 total throws (pitches in game as well as all warm-up pitches and other throws during game). In comparison, on a day a player did not pitch, he averaged 119 ± 102 throws. Across all pitchers, 32% of all throws were low intensity, 54% were medium intensity, and 15% were high intensity. The player with one of the highest percentages of high-intensity throws did not pitch as their primary position, while the 2 players who pitched most often had the lowest percentages. Conclusion: Total throw count can be successfully quantified using a single inertial sensor. Total throws tended to be higher on days a player pitched compared with regular game days without pitching. Clinical Relevance: This study provides a fast, feasible, and reliable method to obtain pitch and throw counts so that more rigorous research on contributing factors to arm injury in the youth athlete can be achieved.

Using Sensors for Player Development: Assessing Biomechanical Factors Related to Pitch Command and Velocity.

Pitching biomechanical research is highly focused on injury prevention with little attention to how biomechanical data can facilitate skill development. The overall purpose of this study was to explore how sensor-derived segment kinematics and timing relate to command and ball velocity during baseball pitching. We used a cross-sectional design to analyze a series of pitches thrown from 10 collegiate baseball pitchers. We collected biomechanical data from six inertial sensors, subjective command from the pitchers, and ball velocity from a radar device. Stepwise regression analyses were used to explore biomechanical variables associated with command for all pitches and ball velocity for fastballs only. We found that only peak forearm linear acceleration was significantly associated with command, whereas several segment kinematic measures were significantly associated with ball velocity. Our results suggest that different biomechanical variables are linked to specific pithing skills. Our findings suggest that end-effector (forearm) movement is more important for pitch command, whereas proximal-to-distal (pelvis, trunk, upper arm, forearm) segmental movement is important for ball velocity.

Sensor Location Matters When Estimating Player Workload for Baseball Pitching.

Estimating external workload in baseball pitchers is important for training and rehabilitation. Since current methods of estimating workload through pitch counts and rest days have only been marginally successful, clubs are looking for more sophisticated methods to quantify the mechanical loads experienced by pitchers. Among these are the use of wearable systems. While wearables offer a promising solution, there remains a lack of standards or guidelines for how best to employ these devices. As a result, sensor location and workload calculation methods vary from system to system. This can influence workload estimates and blur their interpretation and utility when making decisions about training or returning to sport. The primary purpose of this study was to determine the extent to which sensor location influences workload estimate. A secondary purpose was to compare estimates using different workload calculations. Acceleration data from three sensor locations-trunk, throwing upper arm, and throwing forearm-were collected from ten collegiate pitchers as they threw a series of pitches during a single bullpen session. The effect of sensor location and pitch type was assessed in relation to four different workload estimates. Sensor location significantly influenced workload estimates. Workload estimates calculated from the forearm sensor were significantly different across pitch types. Whole-body workload measured from a trunk-mounted sensor may not adequately reflect the mechanical loads experienced at throwing arm segments. A sensor on the forearm was the most sensitive to differences in workloads across pitch types, regardless of the calculation method.

Physical Activity Patterns in Frail and Nonfrail Patients With End-Stage Liver Disease.

Background: Frailty commonly complicates cirrhosis and is associated with poorer outcomes. While patients with cirrhosis may be sedentary, there are few comprehensive descriptions of their physical activity (PA) patterns related to frailty. Our aim was to identify PA characteristics that may be used in interventions to improve PA and reduce frailty. Methods: In a cross-sectional cohort study, forty patients with cirrhosis (mean age 63; 30 nonfrail, 10 frail) wore an accelerometer/thermal sensing armband for 7 days. Postural status (e.g., upright movement, upright sedentary, lying down), Metabolic Equivalent of Tasks (METs) and active bouts were identified. Results: Patients were highly sedentary most of the time (89 ± 7% and 85 ± 10% of the day, in frail and nonfrail cirrhotics, respectively). Compared with nonfrail cirrhotics, frail patients spent significantly shorter amount of time moving in an upright position (7% ± 5 vs. 12% ± 5, P = 0.013 in frail and nonfrail cirrhotics, respectively), had significantly fewer and shorter durations of active bouts per day (number of active bouts: 9 ± 12 vs. 19 ± 14; duration: 13.2 ± 1.5 min and 15.9 ± 2.6 min in frail and nonfrail cirrhotics, respectively), and had a lower amount of steps per wear time hours (41.7 ± 37.1 vs. 116.8 ± 85.4, P = 0.003 in frail and nonfrail, respectively). Traditional measures such as METs or aerobic bouts did not differ between groups. Conclusions: Active bout measures, as opposed to more traditional measures such as METs, differentiate between frail and nonfrail cirrhotics suggesting they may be used to assess changes resulting from targeted interventions to improve physical activity.

Running Injury Paradigms and Their Influence on Footwear Design Features and Runner Assessment Methods: A Focused Review to Advance Evidence-Based Practice for Running Medicine Clinicians.

Many runners seek health professional advice regarding footwear recommendations to reduce injury risk. Unfortunately, many clinicians, as well as runners, have ideas about how to select running footwear that are not scientifically supported. This is likely because much of the research on running footwear has not been highly accessible outside of the technical footwear research circle. Therefore, the purpose of this narrative review is to update clinical readers on the state of the science for assessing runners and recommending running footwear that facilitate the goals of the runner. We begin with a review of basic footwear construction and the features thought to influence biomechanics relevant to the running medicine practitioner. Subsequently, we review the four main paradigms that have driven footwear design and recommendation with respect to injury risk reduction: Pronation Control, Impact Force Modification, Habitual Joint (Motion) Path, and Comfort Filter. We find that evidence in support of any paradigm is generally limited. In the absence of a clearly supported paradigm, we propose that in general clinicians should recommend footwear that is lightweight, comfortable, and has minimal pronation control technology. We further encourage clinicians to arm themselves with the basic understanding of the known effects of specific footwear features on biomechanics in order to better recommend footwear on a patient-by-patient basis.

Measuring markers of aging and knee osteoarthritis gait using inertial measurement units.

Differences in gait with age or knee osteoarthritis have been demonstrated in laboratory studies using optical motion capture (MoCap). While MoCap is accurate and reliable, it is impractical for assessment outside the laboratory. Inertial measurement units (IMUs) may be useful in these situations. Before IMUs are used as a surrogate for MoCap, methods that are reliable, repeatable, and that calculate metrics at similar accuracy to MoCap must be demonstrated. The purpose of this study was to compare spatiotemporal gait parameters and knee range of motion calculated via MoCap to IMU-derived variables and to compare the ability of these tools to discriminate between groups. MoCap and IMU data were collected from young, older, and adults with knee osteoarthritis during overground walking at three self-selected speeds. Walking velocity, stride length, cadence, percent of gait cycle in stance, and sagittal knee range of motion were calculated and compared between tools (MoCap and IMU), between participant groups, and across speed. There were no significant differences between MoCap and IMU outcomes, and root mean square error between tools was ≤0.05 m/s for walking velocity, ≤0.07 m for stride length, ≤0.5 strides/min for cadence, ≤5% for percent of gait cycle in stance, and ≤1.5° for knee range of motion. No interactions were present, suggesting that MoCap and IMU calculated metrics similarly across groups and speeds. These results demonstrate IMUs can accurately calculate spatiotemporal variables and knee range of motion during gait in young and older, asymptomatic and knee osteoarthritis cohorts.

Current Workload Recommendations in Baseball Pitchers: A Systematic Review.

BACKGROUND: Several recommendations have been made regarding pitch counts and workload for baseball players of different levels, including Little League, high school, collegiate, and professional baseball. However, little consensus is found in the literature regarding the scientific basis for many of these recommendations. PURPOSE: The primary purpose of this study was to summarize the evidence regarding immediate and long-term musculoskeletal responses to increasing pitching workload in baseball pitchers of all levels. A secondary purpose of this review was to evaluate the extent to which workload influences injury and/or performance in baseball pitchers. STUDY DESIGN: Systematic review. METHODS: We performed a systematic search in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines for studies addressing physiologic and/or pathologic musculoskeletal changes in response to a quantifiable pitching workload. We included studies examining the effects of pitching workload on performance, injury rate, and musculoskeletal changes in Little League, high school, collegiate, and professional baseball players. RESULTS: We identified 28 studies that met our inclusion and exclusion criteria: 16 studies regarding Little League and high school pitchers and 12 studies regarding collegiate and professional pitchers. The current evidence presented suggests that increased pitching workload may be associated with an increased risk of pain, injury, and arm fatigue in Little League and high school pitchers. However, little consensus was found in the literature regarding the association between pitching workload and physiologic or pathologic changes in collegiate and professional pitchers. CONCLUSION: Evidence, although limited, suggests the use of pitch counts to decrease injury rates and pain in Little League and high school baseball pitchers. However, further research must be performed to determine the appropriate number of pitches (or throws) for players of different ages. This systematic review reported conflicting evidence regarding the use of pitch counts in college and professional baseball. Future high-quality research is required to determine the role, if any, of pitch counts for collegiate and professional pitchers.

Ultrasound elastographic assessment of plantar fascia in runners using rearfoot strike and forefoot strike.

Forefoot strike is increasingly being adopted by runners because it can better attenuate impact than rearfoot strike. However, forefoot strike may overload the plantar fascia and alter the plantar fascia elasticity. This study aimed to use ultrasound elastography to investigate and compare shear wave elasticity of the plantar fascia between rearfoot strikers and forefoot strikers. A total of 35 participants (21 rearfoot strikers and 14 forefoot strikers), who were free of lower limb injuries and diseases, were recruited from a local running club. Individual foot strike patterns were identified through the measured plantar pressure during treadmill running. The B-Mode ultrasound images and shear wave elastographic images of the plantar fascia were collected from each runner. Two independent investigators reviewed the images and examined the plantar fascia qualitatively and quantitatively. The results demonstrated an overall good agreement between the investigators in the image review outcomes (ICC:0.96-0.98, κ: 0.89). There were no significant differences in the fascial thickness (p = 0.50) and hypoechogenicity on the gray-scale images (p = 0.54) between the two groups. Shear wave elastography showed that forefoot strikers exhibited reduced plantar fascia elasticity compared to rearfoot strikers (p = 0.01, Cohen's d = 0.91). A less elastic fascial tissue was more easily strained under loading. Tissue overstrain is frequently related to the incidence of plantar fasciitis. While further study is needed for firm conclusions, runners using forefoot strike were encouraged to enhance their foot strength for better protection of the plantar fascia.

Years of running experience influences stride-to-stride fluctuations and adaptive response during step frequency perturbations in healthy distance runners.

RESEARCH QUESTION: The current study investigated stride-to-stride fluctuations of step rate and contact time in response to enforced step frequency perturbations as well as adaptation and de-adaptation behavior. METHODS: Forty distance runners ran at a self-selected speed and were asked to match five different enforced step frequencies (150, 160, 170, 180, and 190 beats per min). The influence of experience was explored, because running is a skill that presumably gets better with practice, and increased years of running experience is protective against injury. Detrended fluctuation analysis was used to determine the strength of long-range correlations in gait fluctuations at baseline, during the perturbation, and post-perturbation. Adaptive response was measured by the ability to match, rate of matching, and aftereffect of step frequency perturbations. RESULTS: The structure of stride-to-stride fluctuations for step rate and contact time did not change during the perturbation or post-perturbation compared to baseline. However, fluctuations in step rate were affected by the level of perturbation. Runners with the most experience had a less persistent structural gait pattern for both step rate and contact time at baseline. Highly experienced runners also demonstrated the best adaptive response. They better matched the enforced step frequency, reached the enforced step frequency sooner, and returned to preferred step frequency more quickly following removal of the perturbation. SIGNIFICANCE: These findings indicate baseline locomotor flexibility may be beneficial to achieve task demands and return to a stable state once the task is complete. Increased locomotor flexibility may also be a contributing factor for reduced injury risk in experienced runners.

Risk Factors for Baseball-Related Arm Injuries: A Systematic Review.

BACKGROUND: Contributing factors for arm injuries among baseball players have been described. However, no review has systematically identified risk factors with findings from prospective cohort studies. PURPOSE: To systematically review prospective cohort studies that investigated risk factors for arm injury among baseball players. STUDY DESIGN: Systematic review; Level of evidence, 3. METHODS: Electronic databases were searched for relevant English-language studies. Titles, abstracts, and full-text articles were screened by 2 blinded reviewers to identify only prospective cohort studies and randomized controlled trials. Two independent investigators screened each article for appropriate criteria. RESULTS: Fourteen prospective articles were selected for this review. Youth, high school, and professional baseball players (N = 2426) were pooled, and 43 risk factors were assessed in relation to general arm, shoulder, and elbow injuries. All studies evaluated players for at least 1 season. Deficits in preseason shoulder range of motion and strength were significant risk factors for general arm or shoulder injury among high school and professional players. Elbow and shoulder varus torque at peak external shoulder rotation during pitching, high pitch velocity, and shoulder rotational and flexion deficits were risk factors for elbow injuries among professional pitchers. Pitching >100 innings in 1 year, being aged 9 to 11 years, being a pitcher or catcher, training >16 hours per week, and having a history of elbow pain were significant risk factors for elbow injury among youth players. CONCLUSION: History of elbow pain and age had a high risk of associated elbow injury among youth players. Training or pitching load also increased elbow injury risk for youth athletes. Loss of shoulder range of motion appears to increase risk for elbow injury among professional athletes. Single time-point data collections per season, studies with the same sample population, and studies with self-reported injury and risk factor data may limit the interpretation of these findings. Health care professionals should use caution when assessing injury risk during evaluation and making decisions about the training workload and playing time of baseball players.

Segment Coordination Variability Differs by Years of Running Experience.

Running is a popular activity that results in high rates of overuse injury, with less-experienced runners becoming injured at higher rates than their more-experienced peers. Although measures of joint kinematics and kinetics and ground reaction forces have been associated with overuse running injuries, similar differences across levels of running experience have not been found. Because running is a motor skill that may develop with experience, an analysis of segment coordination and its variability could provide additional insight into why injury incidence decreases with increasing experience. PURPOSE: The purpose of this study was to determine if less-experienced runners have different segment coordination and lower segment coordination variability compared with their more-experienced peers. METHODS: This retrospective analysis included 20 more-experienced (≥10 yr running) and 21 less-experienced (≤2 yr running) runners. Sagittal thigh versus shank and shank versus foot segment coordination and coordination variability were calculated using a modified vector coding approach as individuals ran on a treadmill at preferred pace. Coordination and its variability were compared between groups during terminal swing and early, mid, and late stance for both segment couples. RESULTS: Segment coordination was similar between less- and more-experienced runners. Less-experienced runners had lower segment coordination variability compared with more-experienced runners for both the thigh versus shank and shank versus foot couples. This lower variability occurred during early and mid stance. CONCLUSIONS: Runners appeared to attain stable segment coordination patterns within 2 yr of consistent running, but had lower coordination variability compared with individuals who had been running for 10 or more years. These results suggest that assessment of movement patterns and their flexibility may help inform injury prevention or treatment strategies for less-experienced runners.

Experience does not influence injury-related joint kinematics and kinetics in distance runners.

PURPOSE: Increased running experience and more time spent running appears to be advantageous in reducing injury risk, although the reason behind this is unclear. It is plausible that more experience results in better running mechanics leading to less injuries. Running mechanics are often screened during clinical assessments and targeted for correction in gait retraining, particularly those thought to be global indicators of injury or those associated with elevated knee joint loading. Examining the biomechanics of runners who are less-injury prone can improve our understanding of the significance of faulty running mechanics in relation to injury. Our goal was to examine if running experience was correlated to differences in kinematics and kinetics associated with increased knee joint loading and running-related injury risk. METHODS: One hundred runners with varying experience ran on a pressure-sensing treadmill at a self-selected speed. Trunk and lower extremity kinematics, spatiotemporal measures, and ground reaction forces were collected. Multiple linear regression was used to assess the association between experience and three-dimensional hip kinematics, sagittal plane lower-extremity mechanics, and ground reaction forces while controlling for age and speed. RESULTS: Increased running experience was not significantly associated with running mechanics. Increased age was significantly associated with reduced peak knee flexion and increased contact time. Running speed influenced several spatiotemporal, kinematic, and kinetic variables. CONCLUSION: Increased years of running experience does not appear to significantly influence running mechanics. However, age and running speed do influence biomechanical variables associated with injury in distance runners. Thus, there may be factors, other than running mechanics, that contribute to less risk in more experienced runners.

The effect of unilateral arm swing motion on lower extremity running mechanics associated with injury risk.

Many field sports involve equipment that restricts one or both arms from moving while running. Arm swing during running has been examined from a biomechanical and physiologic perspective but not from an injury perspective. Moreover, only bilateral arm swing suppression has been studied with respect to running. The purpose of this study was to determine the influence of running with one arm restrained on lower extremity mechanics associated with running or sport-related injury. Fifteen healthy participants ran at a self-selected speed with typical arm swing, with one arm restrained and with both arms restrained. Lower extremity kinematics and spatiotemporal measures were analysed for all arm swing conditions. Running with one arm restrained resulted in increased frontal plane knee and hip angles, decreased foot strike angle, and decreased centre of mass vertical displacement compared to typical arm swing or bilateral arm swing restriction. Stride length was decreased and step frequency increased when running with one or both arms restrained. Unilateral arm swing restriction induces changes in lower extremity kinematics that are not similar to running with bilateral arm swing restriction or typical arm swing motion. Running with one arm restrained increases frontal plane mechanics associated with risk of knee injury.

Single-Leg Squat Performance in Active Adolescents Aged 8-17 Years.

Agresta, CE, Church, C, Henley, J, Duer, T, and O'Brien, K. Single-leg squat performance in active adolescents aged 8-17 years. J Strength Cond Res 31(5): 1187-1191, 2017-More than 30 million U.S. adolescents participate in sport and exercise. Lower extremity injury from sport participation accounts for up to 89% of injuries each year. The single-leg squat (SLS) is a simple clinical tool that assesses lower extremity mechanics often associated with injury risk. To date, there is limited information regarding SLS performance in healthy children. Such information could be useful when assessing youth athletes to determine if mechanics demonstrated are different than is to be expected and puts them at the risk for injury. Furthermore, maturity status is thought to influence motor performance. Currently, there is no information regarding the influence of maturity status on SLS performance in adolescents. The purpose of our study was to determine SLS performance in relation to age and maturity level in adolescents. Forty-five children aged 8-17 years were videotaped performing a series of 10 squats using a standardized protocol. Standing height, seated height, and leg length measures were collected. Investigators scored the SLS test using specific scoring criteria. Adolescents were categorized into 3 maturity levels using a peak height velocity calculation. Multiple linear regression analyses and analysis of variance were used to analyze the data. Chronological age was a significant predictor of SLS performance with younger children having poorer SLS scores. Coaches and trainers should consider the chronological age of the youth athlete when assessing SLS performance. Furthermore, tailored training programs by age may help to address faulty areas, like single-leg stability, and improve overall functional performance.

Gait Retraining for Injured and Healthy Runners Using Augmented Feedback: A Systematic Literature Review.

STUDY DESIGN: Systematic literature review. OBJECTIVES: This review sought to determine the efficacy of real-time visual and/or auditory feedback for modifying kinematics and kinetics during running gait. BACKGROUND: Real-time visual and auditory feedback has gained popularity in the clinical and research settings. Rehabilitation time and injury prevention may be improved when clinicians are able to modify running mechanics in a patient population. METHODS: A thorough search of PubMed, CINAHL, and Web of Science from 1989 to January 2015 was performed. The search sought articles that examined real-time visual or auditory feedback for the purposes of modifying kinematics or kinetics in injured or healthy runners. Study design and methodological quality were rated using a 20-point scale. RESULTS: Ten studies were identified for inclusion in the review, 2 of high and 8 of moderate methodological quality. There was a consensus in the literature that the use of real-time feedback is effective in reducing variables related to ground reaction forces, as well as in positively modifying previously identified risky lower extremity kinematic movement patterns in healthy runners and those with patellofemoral pain and chronic exertional compartment syndrome. No one method of feedback was identified as being superior. Mirror and 2-dimensional video feedback were identified as potential methods for running-gait modification in a clinical setting. CONCLUSION: In conjunction with traditional therapeutic interventions, real-time auditory and visual feedback should be considered for treating injured runners or addressing potentially injurious running mechanics in a healthy population.