Sports Sciences Commons^™

A Preschool Obesity Prevention Program Is Associated With Improvements On Physical Activity Quality, Fernando Juarez Jr., Azeem A. Hussain, Shiyu Li, Vanessa Estrada, Jill Johnstone, Zenong Yin, Erica Sosa

International Journal of Exercise Science: Conference Proceedings

The Míranos! Look at Us We Are Healthy (Míranos!) is an eight-week pilot intervention to promote healthy weight gain in low-income preschool Latino children aged 3-5 years. A major focus is to increase time spent in physical activity level, especially moderate to vigorous physical activity (MVPA) during play time and improve class instruction quality. According to one published study, preschool children spent only 14% of play session time in MVPA and 73% in sedentary activity (Tandon, 2015). PURPOSE: To assess the effectiveness of the Míranos! pilot intervention on the quality (lesson context, and health promotion interactions) and level of …

Effects Of A Head Start Obesity Prevention Pilot On Preschoolers’ Physical Activity, Shiyu Li, Azeem A. Hussain, Fernando Juarez, Vanessa Estrada, Erica Sosa, Derek P. Hales, Zenong Yin

International Journal of Exercise Science: Conference Proceedings

Regular participation in physical activity (PA) is important for the healthy growth and development of preschoolers. The Míranos! Look at Us We Are Healthy (Míranos!) is an obesity prevention intervention with age-appropriate structured and unstructured outdoor/indoor play and classroom activities led by teacher. As an objective instrument to provide information on human movements, accelerometer can accurately identify the levels of physical activity and assess the effects of physical activity intervention. PURPOSE: to evaluate the effects of an 8-week Míranos! pilot intervention on increasing physical activity levels during school time in preschoolers. METHODS: Study participants were children aged 3-5 years enrolled …

Racial Differences In Vascular Function In Response To Mental Stress, Bryon Matthew Curtis, John Akins, Jordan C. Patik, Guillermo Olvera, Aida Nasirian, Jeremiah Campbell, R Matthew Brothers

International Journal of Exercise Science: Conference Proceedings

African Americans (AA) have a higher prevalence of hypertension and other cardiovascular (CV) complications compared to other populations. While the reasons for this elevated CV disease risk are multifactorial, vascular dysfunction is a key contributing factor. It has been previously shown that mental stress, induced by mental arithmetic, results in a significant increase in forearm blood flow (FBF). This response has been predominantly attributed to the release and vasodilatory effect of Nitric Oxide (NO). In this regard, a previous study has reported that AA have an attenuated increase in FBF as compared to Caucasians (CA) in response to mental stress, …

An Eight-Week Physical Activity Intervention Is Associated With Gross Motor Skills In Preschool Children, Azeem A. Hussain, Fernando Juarez Jr., Shiyu Li, Vanessa Estrada, Jill Johnstone, Erica T. Sosa, Zenong Yin

International Journal of Exercise Science: Conference Proceedings

The preschool age (three to five years old) is critical in developing gross motor skills. Additionally, children with higher fundamental movement skills are more likely to participate in high levels of physical activity (Han, Fu, Cobley, & Sanders, 2018). PURPOSE: To determine if the eight-week physical activity (PA) pilot intervention program is associated with gross motor development in preschool children ages three to five years old. METHODS: Study participants were 35 children (average age=3.74 (SD 0.74); 82.67% Hispanics, 8.57% African American, 2.86% white, and 5.71% others) enrolled in two Head Start Centers in San Antonio, Texas. Gross motor …

Chronic Effects Of An Elevation Training Mask On Aerobic Capacity, Anaerobic Endurance, And Pulmonary Function, Tyler Heimdal, Lavan Rajan, Justin Vickery, Ujalashah Dhanani, Joshua Harris, Michael Moreno, David Huston, Patrick Mcculloch, Bradley Lambert

International Journal of Exercise Science: Conference Proceedings

Elevation training masks (ETM) have become popular in active/training populations to enhance performance via purported adaptations associated with altitude and respiratory muscle training. PURPOSE: To compare the effect of training with (TM) to without (CON) wearing the ETM. METHODS: 22 heathy adults (TM: ♂5, ♀6; 27.64±0.86 yr; 23.17±0.88 kg∙m² | CON: ♂5, ♀6; 29.91±1.63 yr; 24.75±1.03 kg∙m²) provided informed consent for this study. VO­₂max and time to exhaustion were assessed (Bruce protocol GXT, w/ & w/o ETM). Anaerobic endurance was assessed using two consecutive 300-yrd shuttle sprints (5min rest). Pulmonary function was assessed using …

Persistent Impairment In Cerebral Vasoreactivity In Subacute Phase Following Concussion, Sydney H. Lyng, Justin Frantz, Madeline Wainman, Tonia Sabo, Kathleen Bell, Sushmita Purkayastha

International Journal of Exercise Science: Conference Proceedings

Concussion diagnosis is characterized by a lack of objective markers, as there is a paucity of better understanding of the pathophysiology. Cerebral vasoreactivity (CVR), an important factor in cerebral blood flow (CBF) regulation with dynamic changes in metabolism can be assessed utilizing manipulation of arterial carbon dioxide. CVR utilizing transcranial Doppler ultrasonography may be a useful, objective vascular biomarker for physiological recovery. PURPOSE: To determine the link between clinical symptoms and CVR on Day-3, Day-21, and Day-90 following a concussion in comparison to the non-injured controls. METHODS: Twenty-seven male and female collegiate athletes (21 ±1years) sustaining a sports-related …

Dual Wavelength Diffuse Correlation Spectroscopy: A Novel Tool For Identifying Determinants Of Oxygen Consumption, Ryan Rosenberry, Chandan-Ganesh Bangalore-Yogananda, Susie Chung, Madison Munson, Wesley J. Tucker, Ye Zhu, Mark J. Haykowsky, Fenghua Tian, Michael Nelson

International Journal of Exercise Science: Conference Proceedings

Near-infrared diffuse correlation spectroscopy (DCS) is a novel method for measuring microvascular skeletal muscle blood flow. Our lab recently found excellent agreement between single wavelength DCS and Doppler ultrasound of the brachial artery during rhythmic handgrip exercise. PURPOSE: Here, we report new data utilizing a dual wavelength DCS system (785nm and 852nm), which extends our prior work by combining novel microvascular perfusion assessment with real-time quantification of tissue oxygenation. METHODS: We enrolled eight individuals (male/female: 3/5, mean: age 48±22 (range: 22-76 years), height 170±8cm, and weight 75±12kg). Subjects were instrumented with the DCS probe placed over the belly of …

Stress Testing For Diastolic Dysfunction: An Old Approach To A New Question, T. Jake Samuel, Rhys Beaudry, Mark J. Haykowsky, Satyam Sarma, Michael D. Nelson

International Journal of Exercise Science: Conference Proceedings

BACKGROUND: Currently, conventional cycle echocardiography is the recommended method for diagnosing diastolic dysfunction in patients with unexplained dyspnea upon exertion. However, this method has several underlying limitations including movement and respiratory artifact. These limitations are often exaggerated in patients who are obese and suffer from exertional dyspnea, and therefore limit its application in clinical diagnosis. Our group recently demonstrated that isometric handgrip echocardiography is a powerful sub-clinical diastolic discriminator that avoids the limitations of conventional cycle echocardiography and that can be easily implemented in the clinic. PURPOSE: However, to date it remains unclear how these two methodologies compare, and thus …

Exploiting Arm Swinging Dynamics To Reduce The Metabolic Cost Of Walking While Carrying Loads, Obioma B. Mcreynolds, Christopher J. Arellano

International Journal of Exercise Science: Conference Proceedings

Arm swing while walking at one’s optimal speed is primarily driven by passive pendulum mechanics, an energy saving mechanism that has been speculated to incur little to no metabolic cost. PURPOSE: In line with this idea, we set out to determine whether carrying loads on the swinging and non-swinging arms while walking would be less costly than carrying loads at other locations on the body. We hypothesized that carrying loads on the arms while restricted from swinging would demand a greater metabolic cost than carrying loads on the arms while naturally swinging. For relative comparisons, we also explored the cost …

Evidence Of Racial Differences In Microvascular Function Among College-Aged Women, Jordan C. Patik, Bryon M. Curtis, John D. Akins, Aida Nasirian, Guillermo Olvera, R Matthew Brothers

International Journal of Exercise Science: Conference Proceedings

Microvascular dysfunction contributes to the development of hypertension and insulin resistance. The black population is at an elevated risk of both conditions relative to other racial groups. Previous studies indicate that college-aged black men, compared to their white counterparts, have impaired microvascular function as assessed by post-occlusion reactive hyperemia (RH). It is unknown whether this racial disparity is present in healthy, young adult black (BW) and white women (WW). Furthermore, whether nitric oxide-mediated cutaneous microvascular hyperemia during local heating (LH) is different in these populations has not been determined. Purpose: The purpose of this study was to test the hypothesis …

Associations Between Leg Lean Mass And Arterial Function In Pre-Menopausal And Post-Menopausal Women., Stephen M. Fischer

International Journal of Exercise Science: Conference Proceedings

Vascular dysfunction has been associated to sarcopenia, the age-related impairment in skeletal muscle mass, strength, and performance, in postmenopausal women. Previous research has shown inverse relationships between leg lean mass (LM) and arterial stiffness (measured as carotid to femoral pulse wave velocity, cfPWV) or pressure wave reflection (augmentation index, AIx) in men and women. AIx is an appropriate vascular marker in young but not middle-age/older adults, especially in women.

Purpose: To examine the associations between leg LM and arterial function (cfPWV and aortic AIx adjusted to 75bpm (AIx@75)) in pre-menopausal (PRE-M) and post-menopausal (POST-M) women. Methods: 47 women (24 PRE-M, …

Skeletal Muscle Oxygenation During Plantarflexion Exercise In Young-Old And Older-Old Adults, Arun Maharaj, Salvador J. Jaime, Justin Mason, Patrick Saracino, Arturo Figueroa

International Journal of Exercise Science: Conference Proceedings

The aging process is associated with a gradual decrease in exercise performance, leg muscle blood flow and oxygenation, and endothelial vascular reactivity. Purpose: To examine potential differences in femoral artery flow-mediated dilation (fa-FMD) and calf muscle oxygenation (HbO₂) during low-intensity plantarflexion exercise in older adults. Methods: 43 young-old (YO; n=24, 67 ± 1 years) and older-old (OO: n=19, 70 ± 1 years) individuals were included in this study. We measured body fat % and leg lean mass (LLM) by DEXA and handgrip maximal voluntary contraction (MVC) using a dynamometer. VO_2max was estimated using a submaximal treadmill test. …

Accuracy Of Fitbit Surge And Smartphone Apps At Measuring Cycling Distance And Speed, Jose L. Gamez Jr., Ivan A. Figueroa, Merrill D. Funk

International Journal of Exercise Science: Conference Proceedings

There are many smartphone apps that measure distance and speed of cycling, however, there is no research on the accuracy of this cycling apps. PURPOSE: To determine the accuracy of Fitbit Surge and two smartphone applications at measuring distance and speed while cycling outside. METHODS: Thirteen college-aged students (Mean±SD; BMI: 25.2±3.0kg/m²; 10 males, 3 females) consented to participate in one measurement session. A 0.75 mile route along a sidewalk around the university campus was used for 3 separate trials using a mountain bike. A Fitbit (FB) along with an Android smartphone running Google-Fit (G-Fit) and S-Health (SH) were …

Ability Of The Functional Movement Screen (Fms) To Predict Injury In Ncaa Division Ii Track And Field Athletes And The Association Between The Fms, Eccentric Hip Abduction Strength, And Injury Risk, Shane Purser, Collin Brown, Teresa Huckaby, Shelly Weise

International Journal of Exercise Science: Conference Proceedings

A high injury rate is present in the collegiate cross country and track population. Currently no gold standard measurement exists to predict future injury. The FMS and eccentric hip strength are two potential measures to predict future injury risk. PURPOSE: To establish if the 100 point FMS and 21 point FMS scores are correlated with injury risk among NCAA Division II cross country and track and field athletes, as well as determine if hip strength is associated with injury risk or FMS score. METHODS: This investigation was an exploratory prospective cohort study of eight Division II cross country …

Assessment Of Travis County Health Disparities And Child Obesity Rates, David Rodriguez

International Journal of Exercise Science: Conference Proceedings

BACKGROUND: The youth obesity epidemic in the United States represents a prevalence of health challenges that can potentially lead to future preventable diseases. There are many factors that contribute to the ongoing obesity epidemic in America. PURPOSE: This study investigated the correlation between environmental factors, behavioral factors, socioeconomic status (SES), and obesity/overweight rates among school grade children within Travis County. We aimed to identify risk factors that contribute to obesity rates on the national, state, and Travis County levels. METHODS: We researched, contacted school district representatives, and photographed two Travis County school districts on opposite ends of the SES …

Validity Of Bmi-Based Equations For Estimating Body Fat Percentage In Collegiate Male Soccer Players: A Three-Compartment Model Comparison, Alexandra Loredo, Kassandra A. Jaramillo, Brett S. Nickerson

International Journal of Exercise Science: Conference Proceedings

The ease of calculating body mass index (BMI)-based body fat percentage (BF%) is appealing in collegiate male soccer player who have limited time availability and strict training regimens. However, research has yet to evaluate whether BMI-based BF% equations are valid when compared to a criterion multi-compartment model. PURPOSE: The purpose of this study was to compare BMI-based BF% equations with a three-compartment (3C) model in collegiate male soccer players. METHODS: Sixteen NCAA Division II male soccer players (age = 21 ± 2 years; ht = 179.0 ± 8.2 cm; wt = 78.0 ± 8.5 kg) participated in this study. BMI …

Exercise-Induced Th17 Lymphocyte Response And Their Relationship To Cardiovascular Disease Risk Factors In Obese, Post-Menopausal Women, Maria A. Cardenas, Michael M. Levitt, Bryan Richie, Shaohan Lu, Elise Erickson, Carmen Cook, Jay Haynes, Andreas Kreutzer, Joel B. Mitchell, Melody D. Phillips

International Journal of Exercise Science: Conference Proceedings

Obesity-induced inflammation promotes type 2 diabetes and cardiovascular disease (CVD). A causative link between adaptive immunity and pathogenesis of obesity-associated diseases has been established. PURPOSE: To examine the effects of exercise on circulating T-helper (Th) 17 lymphocytes in overweight/obese post-menopausal women. METHODS: Twenty-seven overweight/obese women (BMI 32.7 ± 5.1 kg×m^-2, 55-75 yr) were randomly assigned to the exercise (EX, n=14) or education (ED, n=13) groups. EX performed a 25-min walk (75-80% HRR) and 2 sets of 8 resistance exercises (70-80% 1RM) with blood samples obtained at: pre-exercise, post-exercise, one-hour and two-hour post-exercise. Blood samples were obtained …

Accelerometer-Determined Physical Activity And Sedentary Behavior Among Majority-Minority Sample Of Adults: The Houston Train Study, Ashleigh Johnson, Kelley Pettee Gabriel, Deborah Salvo, Erin Dooley, Casey Philip Durand, Gregory Knell, Samantha Kreis, Harold W. Kohl Iii

International Journal of Exercise Science: Conference Proceedings

Based on self-reported data, minority populations are often found to be less active compared to whites, which may contribute to overall health disparities. The Houston Travel Related Activity in Neighborhoods (TRAIN) Study provides an opportunity to examine differences in accelerometer-determined physical activity levels among a majority-minority sample of adults. PURPOSE: To describe and examine differences in accelerometer-determined physical activity and sedentary behavior among TRAIN participants at baseline, by race/ethnic groups and sex. METHODS: Study participants were part of an ongoing natural experiment of transportation-related physical activity. At baseline, a group of participants self-selected to wear an ActiGraph wGT3X-BT …

Accuracy Of Fitbit Charge 2 At Estimating Vo2max, Calories, And Steps On A Treadmill, Naomi D. Lucio, Elvia V. Salazar, Ivan A. Figueroa, Jose L. Gamez, Ryan D. Russell, Merrill D. Funk

International Journal of Exercise Science: Conference Proceedings

Current fitness activity trackers can account for steps, calories burned, heart rate, and distance traveled. A new feature has recently been introduced on the Fitbit Charge 2, “Cardio Fitness Level,” which is comparable to a VO2max score in that it allows consumers to be aware of their aerobic fitness level. PURPOSE: To assess the accuracy of the Fitbit Charge 2 at estimating VO2 score (“Cardio Fitness Level”), calories, and steps when compared to indirect calorimetry and video analyzed steps, respectively. METHODS: Twenty-two healthy adults (Mean±SD; 24.1±4.2yrs; 16.9±9.0%fat; 15 male) completed two separate visits. On the first visit, anthropometric measurements were …

Diet And Sex Differences Induce Unique Alterations Of Markers For Blood Brain Barrier Integrity In Age-Accelerated Mice, Dakota R. Kamm, Kenneth A. Witt, Karin E. Sandoval, Megan L. Schaller, Matthew P. Harris, Joshua S. Wooten

International Journal of Exercise Science: Conference Proceedings

The role of diet on brain health has received significant attention, with the Western diet (WD) contributing to cerebrovascular alterations and neurodegenerative disease. The blood-brain barrier (BBB) may play a particularly important role as it forms the interface between the peripheral circulation and the central nervous system. The WD has been shown to negatively impact the BBB. Whether there are sex specific differences with diet on BBB integrity remains unclear. PURPOSE: To determine the effect of diet and sex on the mRNA expression of markers of BBB integrity in an age-accelerated mouse model. METHODS: Male and female Senescence …

What Determines The Metabolic Cost Of Human Running Across A Wide Range Of Velocities?, Shalaya Kipp, Alena Marie Grabowski, Rodger Kram

International Journal of Exercise Science: Conference Proceedings

The cost of generating force hypothesis proposes that the metabolic rate during running is determined by the rate of muscle force development (1/t_c, t_c=contact time) and volume of active leg muscle. A previous study assumed a constant recruited muscle volume and reported that the rate of force development alone explains ~70% of the increase in metabolic rate for human runners across a moderate velocity range (2-4 m s^-1). PURPOSE: We performed a more systematic analysis of the effective mechanical advantage (EMA) of the lower leg over a wide velocity range to determine if …

Validity Of Cardiorespiratory Fitness Assessment In Adolescents Using The Non-Exercise Test, Pacer, And The K4b2 Portable Metabolic System, Pedro Migliano, Megan James, Allison Hall, Amy Fruge, Anna Flipse

International Journal of Exercise Science: Conference Proceedings

Cardiorespiratory fitness (CRF) is an important indicator of adolescent cardiovascular and future cardiometabolic health. The PACER test is often used to measure CRF in adolescents but is not feasible with pediatric populations unable to perform physical testing secondary to physical impairments. The non-exercise test (NET) has been recommended as a proxy for estimating VO₂ in individuals not able to perform physical tests by using variables such as gender, age, body mass index, resting HR, and self-reported habitual physical activity levels. PURPOSE: The purpose of this study was estimate the concurrent validity of the NET for adolescents against the PACER …

Metabolic Responses To A Battling Rope Protocol Performed In The Seated Or Stance Positions, Dominisha Felder, Kasey Hogan, Reka Kovacs, Hannah Mitchell, Wayne Brewer

International Journal of Exercise Science: Conference Proceedings

Achieving the recommended amount of physical activity is a greater challenge for individuals who are disabled than those who are not disabled. Battling ropes is an intense exercise that has been shown to promote elevation of heart rate and increased oxygen consumption, and may be a beneficial exercise alternative for individuals with disabilities. PURPOSE: To compare the levels of perceived exertion (RPE), oxygen consumption (VO₂) and heart rate (HR) responses elicited by a treadmill (TM) or bicycle (BK) VO₂ max test with a standing or sitting battling rope protocol (BRP) (TM vs. standing BRP) (BK vs. …

The Comparison Of High-Intensity Interval Exercise Vs. Continuous Moderate-Intensity Exercise On C1q/Tnf-Related Protein-9 Expression And Flow-Mediated Vasodilation In Obese Individuals, Brandon G. Fico, Ryan S. Garten, Michael C. Zourdos, Michael Whitehurst, Peter J. Ferrandi, Katelyn M. Dodge, Gabriel Pena, Alexandra A. Rodriguez, Chun-Jung Huang

International Journal of Exercise Science: Conference Proceedings

PURPOSE: A recent novel adipocytokine, C1q/TNF-related protein-9 (CTRP9), has been shown to increase activation of endothelial nitric oxide synthase and reduce vasoconstrictors (e.g., endothelin-1). In addition, CTRP9 may play a compensatory role in obesity-related endothelial dysfunction. Although there is limited information regarding exercise-mediated CTRP9, high-intensity interval exercise (HIIE) has been shown to be as or more effective than continuous moderate-intensity exercise (CME) in improving indicators of endothelial function (e.g., brachial artery flow-mediated dilation [BAFMD]). Therefore, the purpose of this study was to investigate the effect of acute HIIE vs. CME on serum CTRP9 and BAFMD responses in obese individuals. METHODS: …

Running Economy While Running In Extreme Cushioning And Normal Cushioning Running Shoes, Miles A. Mercer, Tori M. Stone, John C. Young, John Mercer

Kinesiology and Nutrition Sciences Faculty Research

The purpose of the study was to determine if running economy was influenced by wearing maximal cushioning shoes vs. control (neutral cushioning) shoes. (Please see Abstract in text)

Validation Of The Godin Leisure-Time Exercise Questionnaire Classification Coding System Using Accelerometry In Multiple Sclerosis, Robert W. Motl, Rachel E. Bollaert, Brian M. Sandroff

Exercise Science Faculty Research and Publications

Objective: There have been recent efforts toward creating a health contribution score (HCS) from the Godin Leisure-Time Exercise Questionnaire (GLTEQ) that reflects public-health guidelines for levels of moderate-to-vigorous physical activity (MVPA). The HCS yields categories of insufficiently active (less substantial or low benefits), moderately active (some benefits), and active (substantial benefits). The present study examined the validity of the GLTEQ HCS and its categories as reflecting levels of MVPA in multiple sclerosis (MS). Method: The sample included 684 persons with MS. Participants wore an accelerometer on an elastic belt around the waist above the nondominant hip during the waking hours …

Horse-Related Injuries: Causes, Preventability, And Where Educational Efforts Should Be Focused, Fernanda Camargo, William R. Gombeski Jr., Polly Barger, Connie Jehlik, Holly Wiemers, James Mead, Amy Lawyer

Animal and Food Sciences Faculty Publications

A high percentage of equestrians will experience accidents, with different degrees of severity, throughout their riding careers. Horse-related injuries have the highest likelihood of requiring hospitalization based on individuals visiting US emergency departments. Studies have shown that the majority of injured riders said they could have prevented the accident and the injury was due to rider/handler error. Therefore, equestrians reported their injuries, and a panel of experts analyzed these reports to better understand the causes, how to prevent, and where to invest educational resources to generate a reduction in horse-related accidents. The majority of riders reported intermediate riding skills, most …

Girls In The Boat: Sex Differences In Rowing Performance And Participation, Kevin G. Keenan, Jonathon Senefeld, Sandra K. Hunter

Exercise Science Faculty Research and Publications

Men outperform women in many athletic endeavors due to physiological and anatomical differences (e.g. larger and faster muscle); however, the observed sex differences in elite athletic performance are typically larger than expected, and may reflect sex-related differences in opportunity or incentives. As collegiate rowing in the United States has been largely incentivized for women over the last 20 years, but not men, the purpose of this study was to examine sex differences in elite rowing performance over that timeframe. Finishing times from grand finale races for collegiate championship on-water performances (n = 480) and junior indoor performances (n = 1,280) …

Resting Hormone Alterations And Injuries: Block Vs. Dup Weight-Training Among D-1 Track And Field Athletes, Keith B. Painter, G. Gregory Haff, N. Travis Triplett, Charles Stuart, Guy Hornsby, Mike W. Ramsey, Caleb D. Bazyler, Michael H. Stone

ETSU Faculty Works

Daily undulating periodization (DUP), using daily alterations in repetitions, has been advocated as a superior method of resistance training, while traditional forms of programming for periodization (Block) have been questioned. Nineteen Division I track and field athletes were assigned to either a 10-week Block or DUP training group. Year and event were controlled. Over the course of the study, there were four testing sessions, which were used to evaluate a variety of strength characteristics, including maximum isometric strength, rate of force development, and one repetition maximum (1RM). Although, performance trends favored the Block group for strength and rate of force …

Building A Soccer Dynasty, Carter Bedsole, Gary Buckley

Student Scholarship - College of Business

The soccer world operates as a free market. Buying, selling, and trading of players is vital to the success of a club. A successful soccer club brings a great deal of revenue and growth to a local economy. Therefore, clubs ought to be prudent when signing players. In this paper, we use ordinary least squares regressions on Major League Soccer player data from 2015-2018 to determine the effect strikers and goalkeepers have on team success. In other words, what is the marginal impact of a good striker relative to a bad one? A good goalkeeper relative to a mediocre one? …