Blog: Latest Posts

The Effect of Field Conditions and Shoe Type on Lower Extremity Injuries in American Football ~ Jingzhen (Ginger) Yang, PhD, MPH

American football has the highest rate of lower extremity injuries in comparison to all other team sports [1,2]. Lower extremity injuries in football are often the result of complex intrinsic risk factors, such as position, age, joint flexibility, and muscle tightness, as well as extrinsic risk factors, such as field conditions, shoe-surface interaction, and equipment [3]. However, published epidemiological studies that examine these factors together are scarce and the few studies on surface type alone have yielded conflicting evidence.

Photo by GoIowaState. Used with permission. All rights reserved. Source: flickr

Photo by GoIowaState. Used with permission. All rights reserved. Source: flickr

Our study recently published in the BJSM analyzed data collected from 188 Division I players. All were from a single university football team in the United States, and played during three consecutive seasons (2007-2010).  The study compared lower extremity injury rates among collegiate football players by playing surface and shoe type during football games and practices.

The findings showed that when surface conditions were abnormal (e.g., the temperature was over 82°F, the humidity was over 50 percent, or visible water spots were seen on the surface), the lower extremity injury rate was more than 2.5 times as high. This was particularly evident during practice sessions.

Another rather unanticipated finding of this study, risk for lower extremity injury, was 3.34 times higher on artificial turf as compared to natural grass during games. This trend was not observed during practice sessions. Findings also indicated that shoe type, including number of cleats and height of shoe top, was not associated with lower extremity injury rates.

This represents the third study in the last two years from the United States reporting significantly greater injury risk on artificial turf [4,5]. These results are supported by the previous studies, which found the excessive rotational shoe-surface traction can cause foot fixation, increasing the risk of lower extremity injuries, such as ACL injury [6-9].

With constant directional and speed changes such as cutting, pivoting, starts and stops, and backpedaling associated with football, artificial turfs could likely play a role in non-contact, lower-extremity injuries including medial/lateral collateral tears, anterior/posterior cruciate tears, and damage to the meniscus.

The results from this study may provide an important practical insight for athletic programs when selecting surfaces to best protects their players, and for athletes to select shoes for varying weather conditions in order to avoid injury.

Jingzhen (Ginger) Yang is an Associate Professor in the College of Public Health at Kent State University. Dr. Yang’s research is focused on injury and violence prevention and control among youth and adolescents, specifically sports injury prevention and control. She was a director of Training Core and Team Leader of  one of 11 CDC funded Injury Prevention Research Centers of excellence. In 2010, she was appointed to serve on the Major League Baseball Injury Research Committee.


  1. Hagel BE, Fick GH, Meeuwisse WH.  Injury risk in men’s Canada West University football. Am J Epidemiol. 2003;157(9):825-833. PMID: 12727676.
  2. Fernandez WG, Yard EE, Comstock RD. Epidemiology of lower extremity injuries among U.S. high school athletes. Acad Emerg Med. 2007;14:641-645. PMID: 17513688.
  3. Dvorak J, Junge A. Football injuries and physical symptons: A review of literature. Am J Sports Med. 2000;38(12):S3-S9. PMID: 11032101.
  4. Hershman EB, Anderson R, Bergfeld JA, Bradly JP, Coughlin MJ, Johnson RJ, Spindler KP, Wojtys E, & Powell JW. An Analysis of Specific Lower Extremity Injury Rates on Grass and Field Turf Playing Surfaces in National Football League Games: 2000 – 2009 Seasons. American Journal of Sports Medicine. 2012 Oct;40(10):2200-5.
  5. Dragoo JL, Braun HJ, & Harris AHS. The Effect of Playing Surface on the Incidence of ACL Injuries in National Collegiate Athletic Association American Football. The Knee. 2013 Jun;20(3):191-5.
  6. Kaila R. Influence of modern studded and bladed soccer boots and sidestep cutting on knee loading during match play conditions. Am J Sports Med. 2007;35:1528-1536. PMID: 17395959.
  7. Ekstrand J, Timpka T, Hagglund M. Risk of injury in elite football played on artificial turf versus national grass: a prospective two-cohort study. Br J Sports Med. 2006;40:975-980. PMID: 16990444.
  8. Fuller CW, Clarke L, Molloy MG. Risk of injury associated with rugby union played on articial turf. J Sports Sci. 2010;28(5):563-570. PMID: 20391085.
  9. Meyers MC. Incidence, mechanisms, and severity of game-related college football injuries on FieldTurf versus natural grass: A 3 year prospective study. Am J Sports Med. 2010;38(4):687-697. PMID: 20075177.
Tagged , , , , , , | Comments Off on The Effect of Field Conditions and Shoe Type on Lower Extremity Injuries in American Football ~ Jingzhen (Ginger) Yang, PhD, MPH

Foot orthoses – what do you need to know? ~ Jason Agosta

Do distance runners need foot orthoses? For many, orthoses are a mystery and/or unnecessary adjunct to their running. The following is intended to dispel some myths of orthoses and to assist with guidance in the wearing of orthoses for distance runners.

Enormous variation exists in what orthoses are issued to runners. Whether orthoses should be used –and the type of orthoses worn—depends on many factors.

Photo by HelloImNik. Used with permission. All rights reserved. Source: flickr

Photo by HelloImNik. Used with permission. All rights reserved. Source: flickr

When to use orthoses for distance runners

First, foot orthoses are used to support and control motion of the foot and lower limb. Orthoses are issued to off-load an injured part and assist with managing injury. In some cases orthoses are used to assist prevention of injury in those who have an extensive history of injury.

In my opinion, orthoses should only be worn by distance runners if there is a history of problems that relate to excessive motion and/or asymmetry. In managing distance runners, orthoses are never issued just because a runner is excessively mobile or asymmetrical. It is important to note that an injury history should be evident to justify the use of orthoses in runners. Having either high arched or low arched feet does not always indicate the function of the foot and a predisposition to injury, nor do they always indicate a need for orthoses.

For distance runners, orthoses may be used to assist to off-load an injured part. But as problems settle, it is not unusual to reduce support. This is important,so as to resume and maintain a running gait that the runner has adapted to over many years. Many runners have orthoses that are reduced to at least 50 percent of initial support after injuries resolve. Some runners, depending on injury history and strengthening, will revert back to not running with orthoses. For some , this can sometimes take up to three months from the initial start of wearing orthoses.

How to use orthoses for distance runners

As individuals, we all adapt to our own structure and function. Changing an athlete’s gait with orthoses is difficult and very specific and in many cases, should be very conservative due to years of an individuals’ adaption. Orthoses for distance runners should be conservative in the level of support. This is due not only to a runner needing to adapt, but also to the fact that running involves large repetitive forces. Making any change to runners with orthoses will have great effect on the mechanics of the lower limb due to the applied forces during running being repetitive and between two to three times body weight each step.

Of course, orthoses are not the only means of managing and preventing running injuries. The practitioner and athlete have to be aware that there are many factors to address, including training errors, footwear, surfaces, and efficiency through good postural control and running technique. Orthoses are only one part of an athlete’s measures for treatment and prevention of injury.

Strengthening and being able to run with an efficient gait and modifying training principles are the most important principles that must be adhered to in-conjunction with orthoses use in injury management.

To learn more about the clinical aspects of biomechanics and sporting injuries turn to Chapter 8 in Clinical Sports Medicine.

Jason Agosta is a Podiatrist of 25 years and is also a former Australian representative at the World Cross Country Championships. His pb’s are 13.48 5000m, 29m for 10km. He still runs approximately 50-60kms per week. The above is very much his opinion in managing distance runners. Learn more at


Tagged , , | Comments Off on Foot orthoses – what do you need to know? ~ Jason Agosta

How does one transform “the biggest public health problem of the 21st century” into the biggest opportunity?

How does one transform “the biggest public health problem of the 21st century” into the biggest opportunity? Physical inactivity is estimated to cost the United States about $75 billion in medical costs alone each year.[1] According to the WHO, “3.3 million people die around in the world each year due to physical inactivity, making it the fourth underlying cause of mortality.”[2]

Ever more sedentary lifestyles and the demands of our modern life make inactivity understandable. Unfortunately, understanding alone is not going to resolve what is becoming a potential crisis of global proportions. Action and leadership are needed.

Photo by MilitaryHealth. Used with permission. All rights reserved. Source: flickr

Photo by MilitaryHealth. Used with permission. All rights reserved. Source: flickr

We recognize that individuals need to be motivated to become more self-responsible, accountable for, and engaged in regards to their health and in developing their own positive well-being. Many patients defer responsible for their own health at least in part onto their healthcare providers and the healthcare system.

Healthcare providers, especially physicians, are well positioned to influence positive change in their patients when it comes to physical inactivity. And it doesn’t have to be overwhelming.

How does one transform “the biggest public health problem of the 21st century” into the biggest opportunity? Step by step. Physicians can start by simply taking out their pad and prescribing physical activity. One patient at a time. One illness at a time. Little steps count. Patients need to be reminded that any increase in activity improves health. Take a walk around the block.  Bypass the elevator for the stairs. Clean the house. Get moving. Your body will love you for it.

There are also resources out there to support healthcare practitioners in prescribing exercise. Chapter 60 in Clinical Sports Medicine provides a quick reference exercise prescription guide for common medical conditions: obesity, cardiovascular disease, COPD, diabetes, asthma, cancer, arthritis…they’re all there. Chapter 54 gives exercise prescriptions for neurological conditions and mental health.

More resources can be found at the following sources:

Take advantage of the resources that are out there and commit to prescribing exercise daily. Step by step. Patient by patient.


[1] Centre for Disease Prevention and Control.

[2] Pratt M, Norris J, Lobelo F et al. The cost of physical inactivity: moving into the 21st century. Br J Sports Med bjsports-2012-091810 Published Online First: 7 November 2012

Tagged , | Comments Off on How does one transform “the biggest public health problem of the 21st century” into the biggest opportunity?

Funding for exercise research, is it a priority? ~ Dr. Steven N. Blair

We have a serious problem in exercise science and sports medicine.  This is lack of attention by funding agencies, at least in the United States, to research in these areas.  If this issue interests you, I suggest that you go to a website at the US National Institutes of Health to see how they spend their research dollars.  There are 233 categories of research spending.  The following slide includes spending for nutrition and food categories.

Note that in the current fiscal year, more than $2 billion are spent on Nutrition and Obesity.  Exercise, physical activity, or sports medicine are not even included on the list of 233 categories.  Isn’t physical inactivity at least a big a public health problem as Food Allergies (FY 2013 spending of $33 million as shown on the above table).  How does research funding for exercise, physical activity, and sports medicine compare with other topics in your country?

Dr. Steven N. Blair is Professor in the Departments of Exercise Science and Epidemiology and Biostatistics at the Arnold School of Public Health, University of South Carolina. Dr. Blair is a Fellow in the American College of Epidemiology, Society for Behavioral Medicine, American College of Sports Medicine, American Heart Association, and American Kinesiology Academy; and was elected to membership in the American Epidemiological Society.

Tagged , , | Comments Off on Funding for exercise research, is it a priority? ~ Dr. Steven N. Blair

Risk factors for hamstring muscle strain injury in sport…what’s the evidence? ~ Dr. Tania Pizzari

It is well recognised that hamstring strains are one of the most common –and impactful- injuries in sports, resulting in missed training, games, and events.  Given the potential direct and indirect costs of this injury can be high for athlete, club, or competition, there has been a considerable amount of research into risk factors for hamstring injuries.

For the clinician, sifting through the abundance of studies and combining the results to form a clear picture about risk factors may be difficult task. The large number of studies with often conflicting outcomes and methodologies can overwhelm.   Our study in BJSM (Freckleton & Pizzari, 2013) endeavours to synthesis the literature and combine results using meta-analyses where possible to simplify the research.

Photo by matturick. Used with permission. All rights reserved. Source: flickr

Photo by matturick. Used with permission. All rights reserved. Source: flickr

Not surprisingly, we identified commonly accepted risk factors of older age and past history of hamstring injury as risk factors for hamstring strain.  Interestingly, a number of the isokinetic strength measures frequently utilised for screening athletes (and assumed to be implicated in hamstring injury risk) were not predictive of hamstring injury.

Conventional isokinetic concentric hamstring : quadriceps (H:Q) ratio and hamstring peak torque were not supported as a risk factors.  The quadriceps peak torque was the only strength measure to be identified as a significant risk factor using a meta-analysis.

The analysis included four studies (195 participants) and found that athletes with an increased quadriceps peak torque were at risk of subsequent hamstring injury.   Hamstring to opposite hamstring (H:oppH) results could not be included in a meta-analysis, however the three studies that looked at this strength measure all showed some evidence for a lower ratio being predictive of injury.

The limitation of using isokinetic testing to evaluate risk could be that the position of the lower limb during the testing does not reflect the position where the hamstring injury is most vulnerable to strain in running (Chumanov, Schache, Heiderscheit, & Thelen, 2012).

Evidence for the advantage or disadvantage of hamstring flexibility has been debated for a long time and the analysis showed few results to support flexibility as a risk factor for injury.  The one test that was close to being a significant risk factor was the active knee extension test.  It is noteworthy that this test has also previously been identified as a potentially useful predictor of recurrence of hamstring injury (Warren, Gabbe, Schneider-Kolsky, & Bennell, 2010) and deserves further investigation as a predictor of initial injury.

Flexibility of the quadriceps, hip flexors and ankle joint dorsi-flexion had some evidence for risk, but could not be included in a meta-analysis.

With regard to the meta-analyses only age, past history, and quadriceps peak torque were identified as significant risk factors.  The following factors showed some promise but failed to have the study power to show a meta-analysis result or could not be included in a meta-analysis:  the AKE test, athlete weight, hip flexor flexibility, quadriceps flexibility, ankle dorsi-flexion lunge range of motion, playing position, lower limb joint position sense, and H:H ratio.

Factors that showed little prediction strength for injury included the following: BMI, height, passive length of hamstring, leg dominance, abdominal strength, VO2 max, peak O2 uptake, anaerobic fitness, slump test, single and double leg counter-movement jump, player exposure, jumping ability and height, knee laxity and running speeds.

It should be noted that this review excluded studies aimed at prevention, although such studies might allow some inferences regarding risk factors.  The limitation of including such studies is that they assume that the prevention strategy is in fact targeting a known risk factor and that the strategy actually alters that risk.

There are a number of perceived risk factors that have not yet been studied in the literature, due mostly to the difficult methodology involved in such evaluation.  The posterior thigh pain chapter in Clinical Sports Medicine identifies fatigue as being a relevant consideration in hamstring strain.

The biomechanical changes that occur with fatigue and the timing of hamstring injuries (late in games) is reasonably used to infer fatigue is factor in hamstring injury (Opar, Williams, & Shield, 2012).  Other measures, such as ground conditions, pre-season participation, player workload, and concomitant injury also require further analysis.

The risk for hamstring injuries is recognised as being multi-factorial in nature, however ongoing research will help to identify areas that should be addressed by clinicians and areas that can be discounted when screening, evaluating, and managing athletes.

Dr. Tania Pizzari is a lecturer and researcher in the Department of Physiotherapy at La Trobe University.  She is also a physiotherapist and director of Mill Park Physiotherapy Centre in Melbourne, Australia.


  1. Chumanov, E. S., Schache, A. G., Heiderscheit, B. C., & Thelen, D. G. (2012). Hamstrings are most susceptible to injury during the late swing phase of sprinting. Br J Sports Med, 46(2), 90. doi: 10.1136/bjsports-2011-090176
  2. Freckleton, G., & Pizzari, T. (2013). Risk factors for hamstring muscle strain injury in sport: a systematic review and meta-analysis. Br J Sports Med, 47(6), 351-358. doi: 10.1136/bjsports-2011-090664
  3. Opar, D. A., Williams, M. D., & Shield, A. J. (2012). Hamstring strain injuries: factors that lead to injury and re-injury. Sports Med, 42(3), 209-226. doi: 10.2165/11594800-000000000-00000
  4. Warren, P., Gabbe, B. J., Schneider-Kolsky, M., & Bennell, K. L. (2010). Clinical predictors of time to return to competition and of recurrence following hamstring strain in elite Australian footballers. Br J Sports Med, 44(6), 415-419. doi: 10.1136/bjsm.2008.048181



Tagged , , , , , , | Comments Off on Risk factors for hamstring muscle strain injury in sport…what’s the evidence? ~ Dr. Tania Pizzari