Mark D. Tillman

A Biomechanical Comparison of Back and Front Squats in Healthy Trained Individuals

Gullett, JC, Tillman, MD, Gutierrez, GM, and Chow, JW. A biomechanical comparison of back and front squats in healthy trained individuals. J Strength Cond Res 23(1): 284-292, 2008-The strength and stability of the knee plays an integral role in athletics and activities of daily living. A better understanding of knee joint biomechanics while performing variations of the squat would be useful in rehabilitation and exercise prescription. We quantified and compared tibiofemoral joint kinetics as well as muscle activity while executing front and back squats. Because of the inherent change in the position of the center of mass of the bar between the front and back squat lifts, we hypothesized that the back squat would result in increased loads on the knee joint and that the front squat would result in increased knee extensor and decreased back extensor muscle activity. A crossover study design was used. To assess the net force and torque placed on the knee and muscle activation levels, a combination of video and force data, as well as surface electromyographic data, were collected from 15 healthy trained individuals. The back squat resulted in significantly higher compressive forces and knee extensor moments than the front squat. Shear forces at the knee were small in magnitude, posteriorly directed, and did not vary between the squat variations. Although bar position did not influence muscle activity, muscle activation during the ascending phase was significantly greater than during the descending phase. The front squat was as effective as the back squat in terms of overall muscle recruitment, with significantly less compressive forces and extensor moments. The results suggest that front squats may be advantageous compared with back squats for individuals with knee problems such as meniscus tears, and for long-term joint health.

Dynamic postural control but not mechanical stability differs among those with and without chronic ankle instability

The purpose of this investigation was to compare dynamic postural control and mechanical ankle stability among patients with and without chronic ankle instability (CAI) and controls. Seventy‐two subjects were divided equally into three groups: uninjured controls, people with previous ankle injury but without CAI, and people with CAI. Subjects completed a single‐leg hop‐stabilization task, and then had an anterior drawer test and lateral ankle radiograph performed bilaterally. The dynamic postural stability index was calculated from the ground reaction forces of the single‐leg hop‐stabilization task. Ankle joint stiffness (N/m) was measured with an instrumented arthrometer during the anterior drawer test, and fibula position was assessed from the radiographic image. Patients with previous ankle injuries but without CAI demonstrated higher frontal plane dynamic postural stability scores than both the uninjured control and CAI groups (P<0.01). Patients with and without CAI had significantly higher sagittal plane dynamic postural stability scores (P<0.01) and increased ankle joint stiffness (P=0.045) relative to the control group. The increased frontal plane dynamic postural control may represent a component of a coping mechanism that limits recurrent sprains and the development of CAI. Mechanical stability alterations are speculated to result from the initial ankle trauma.

Decreased static and dynamic postural control in children with autism spectrum disorders

The purpose of this study was to investigate postural control in children with Autism Spectrum Disorders (ASD) during static and dynamic postural challenges. We evaluated postural sway during quiet stance and the center of pressure (COP) shift mechanism during gait initiation for 13 children with ASD and 12 age-matched typically developing (TD) children. Children with ASD produced 438% greater normalized mediolateral sway (p<0.05) and 104% greater normalized anteroposterior sway (p<0.05) than TD children. Consequently, normalized sway area was also significantly greater (p<0.05) in the group with ASD. Similarly, the maximum separation between the COP and center of mass (COM) during quiet stance was 100% greater in the anteroposterior direction (p<0.05) and 146% greater in the resultant direction (p<0.05) for children with ASD. No significant difference was observed in the mediolateral direction, in spite of the 123% greater separation detected in children with ASD. During gait initiation, no group differences were detected in the posterior COP shift mechanism, suggesting the mechanism for generating forward momentum is intact. However, significantly smaller lateral COP shifts (p<0.05) were observed in children with ASD, suggesting instability or an alternative strategy for generating momentum in the mediolateral direction. These results help to clarify some discrepancies in the literature, suggesting an impaired or immature control of posture, even under the most basic conditions when no afferent or sensory information have been removed or modified. Additionally, these findings provide new insight into dynamic balance in children with ASD.

Differences in three intercondylar notch geometry indices between males and females: a cadaver study

The primary purpose of this unique evaluation of cadaveric skeletal geometry was to compare intercondylar notch geometry between males and females. One hundred male skeletons and 100 female skeletons were evaluated. Three indices of notch geometry were calculated from digital photographs of the distal femur: notch width index, notch area index, and notch shape index. Notch shape index for males exceeded that for females (P<0.004). The intercondylar notch appears less round in females and may play a role in causing ACL injuries. Future studies are required to confirm any link between notch geometry and ACL injury.

Measurement and evaluation of dynamic joint stability of the knee and ankle after injury

Injuries to the lower extremity, specifically the knee and ankle joints of the human body can occur in any athletic event and are most prevalent in sports requiring cutting and jumping manoeuvres. These joints are forced to rely on the dynamic restraints to maintain joint stability, due to the lack of bony congruence and the inability of the static restraints to handle the forces generated during functional tasks. Numerous variables (proprioception, postural control, electromyography, kinetics/kinematics, dynamic stability protocols) have been measured to better understand how the body maintains joint stability during a wide range of activities from static standing to dynamic cutting or landing from a jump. While the importance of dynamic restraints is not questioned, a recent impetus to conduct more functional or sport-specific testing has emerged and placed a great deal of emphasis on dynamic joint stability and how it is affected by lower extremity injuries. Evidence suggests that surgery and aggressive rehabilitation will not necessarily restore the deficits in dynamic joint stability caused by injury to the anterior cruciate ligament or lateral ankle ligaments. In today’s athletic society, there is a major push to return athletes to play as quickly as possible. However, the ramifications of those decisions have not been fully grasped. If an athlete is not fully recovered, a quick return to play could start a vicious cycle of chronic injuries or permanent disability.

Self-Assessed Disability and Functional Performance in Individuals With and Without Ankle Instability: A Case Control Study

STUDY DESIGN Single-blind case-control study. OBJECTIVE To compare functional performance and self-assessed disability scores among individuals with and without chronic ankle instability (CAI) and uninjured controls. BACKGROUND After an acute lateral ankle sprain, CAI develops in 40% to 75% of all individuals. However, some individuals, copers, maintain high-level activities after an ankle sprain and do not develop CAI. Studying differences between copers and those with CAI is the first step in developing a clinical battery of tests that can accurately determine which individuals are more likely to develop CAI after an acute lateral ankle sprain. METHODS AND MEASURES Participants were 24 active adults with unilateral CAI (mean +/- SD age, 21.7 +/- 2.8 years), 24 copers (20.8 +/- 1.5 years), and 24 uninjured controls (21.8 +/- 2.6 years). Participants completed 3 questionnaires of self-assessed disability: (1) Foot and Ankle Disability Index, (2) Foot and Ankle Disability Index-Sport, and (3) a questionnaire of ankle function. Four hop tests were also completed: (1) figure-8 hop, (2) side-to-side hop, (3) triple-crossover hop, and (4) single-leg hop for distance. RESULTS Self-assessed disability was significantly different among groups (P<.001), but hop test scores (P = .259) were not. Those with CAI had greater self-assessed disability than copers and uninjured controls. Copers and uninjured controls did not differ in self-assessed disability or functional performance. CONCLUSIONS Self-assessed disability is significantly greater in those with CAI than copersand uninjured controls. However, functional performance, measured by hop tests, did not differ among groups.

Pain Related Fear and Catastrophizing Predict Pain Intensity and Disability Independently Using an Induced Muscle Injury Model

UNLABELLED Timing of assessment of psychological construct is controversial and results differ based on the model of pain induction. Previous studies have not used an exercise-induced injury model to investigate timing of psychological assessment. Exercise-induced injury models may be appropriate for these investigations because they approximate clinical pain conditions better than other experimental stimuli. In this study we examined the changes of psychological constructs over time and determined whether timing of assessment affected the constructs association with reports of pain intensity and disability. One-hundred twenty-six healthy volunteers completed the Fear of Pain Questionnaire (FPQ-III), Pain Catastrophizing Scale (PCS), and Tampa Scale of Kinesiophobia (TSK) prior to inducing muscle injury to the shoulder. The PCS and TSK were measured again 48 and 96 hours postinjury induction. Pain intensity and disability were collected at 48 and 96 hours and served as dependent variables in separate regression models. Results indicated that the FPQ-III had the strongest prediction of pain intensity from baseline to 96 hours. After baseline the PCS and TSK were stronger predictors of pain intensity and disability, respectively. These data provide support for the use of psychological constructs in predicting outcomes from shoulder pain. However, they deviate from the current theoretical model indicating that fear of pain is a consequence of injury and instead suggests that fear of pain before injury may influence reports of pain intensity. PERSPECTIVE The current study provides evidence that fear of pain can be assessed prior to injury. Furthermore, it supports that after injury pain catastrophizing and kinesiophobia are independently associated with pain and disability. Overall these data suggest that timing of psychological assessment may be an important consideration in clinical environments.

Gender and Limb Differences in Dynamic Postural Stability During Landing

ObjectiveTo determine if gender and limb dominance affect dynamic postural stability and vertical ground reaction force data during jump landings. Secondary objective was to assess the reliability of the dynamic postural stability index (DPSI). DesignA mixed model (2 gender×2 limb) repeated measures design was used to determine the effects of gender and limb dominance on dynamic postural stability. Subjects were required to perform a two-legged jump to a height equivalent of 50% of their maximum vertical leap, land on a single-leg and balance for three seconds. SettingSports Medicine Research Laboratory. ParticipantsForty healthy subjects (20 men, 20 women) participated in this investigation. Main Outcome MeasuresThe DPSI and its directional components quantified dynamic postural stability during a single-leg jump landing. Normalized vertical ground reaction force data quantified energy absorption. ResultsDPSI values revealed that females had significantly different dynamic postural stability as compared to males in the vertical plane [T (78)=−4.2, P<0.01], and in the composite score (dynamic postural stability index) [T (78)=−6.3, P<0.01]. In addition, females had significantly higher peak vertical ground reaction forces [T (78)=−13, P=0.01] than males. The DPSI also showed excellent reliability (ICC=0.96), with a 95% confidence interval ranging from 0.94 to 0.97. ConclusionsThe results indicate that females have higher dynamic postural stability scores in the vertical direction as well as the composite score. This suggests that females used different dynamic postural stability strategies than males. There were no side-to-side dynamic postural stability differences between healthy contralateral limbs.

Force and repetition in cycling: possible implications for iliotibial band friction syndrome.

This study examined force and repetition during simulated distance cycling with regard to how they may possibly influence the on-set of the overuse injury at the knee called iliotibial band friction syndrome (ITBFS). A 3D motion analysis system was used to track lower limb kinematics during cycling. Forces between the pedal and foot were collected using a pressure-instrumented insole that slipped into the shoe. Ten recreational athletes (30.6+/-5.5 years) with no known history of ITBFS participated in the study. Foot-pedal force, knee flexion angle and crank angle were examined as they relate to the causes of ITBFS. Specifically, foot-pedal force, repetition and impingement time were calculated and compared with the same during running. A minimum knee flexion angle of approximately 33 degrees occurred at a crank angle of 170 degrees. The foot-pedal force at this point was 231 N. This minimum knee flexion angle falls near the edge of the impingement zone of the iliotibial band (ITB) and the femoral epicondyle, and is the point at which ITBFS is aggravated causing pain at the knee. The foot-pedal forces during cycling are only 18% of those occurring during running while the ITB is in the impingement zone. Thus, repetition of the knee in the impingement zone during cycling appears to play a more prominent role than force in the on-set of ITBFS. The results also suggest that ITBFS may be further aggravated by improper seat position (seat too high), anatomical differences, and training errors while cycling.

Discriminating Between Copers and People With Chronic Ankle Instability

CONTEXT Differences in various outcome measures have been identified between people who have sprained their ankles but have no residual symptoms (copers) and people with chronic ankle instability (CAI). However, the diagnostic utility of the reported outcome measures has rarely been determined. Identifying outcome measures capable of predicting who is less likely to develop CAI could improve rehabilitation protocols and increase the efficiency of these measures. OBJECTIVE To determine the diagnostic utility and cutoff scores of perceptual, mechanical, and sensorimotor outcome measures between copers and people with CAI by using receiver operating characteristic curves. DESIGN Case-control study. SETTING Sports medicine research laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty-four copers (12 men, 12 women; age = 20.8 ± 1.5 years, height = 173 ± 11 cm, mass = 78 ± 27 kg) and 24 people with CAI (12 men, 12 women; age = 21.7 ± 2.8 years, height = 175 ± 13 cm, mass = 71 ± 13 kg) participated. INTERVENTION(S) Self-reported disability questionnaires, radiographic images, and a single-legged hop stabilization test. MAIN OUTCOME MEASURE(S) Perceptual outcomes included scores on the Foot and Ankle Disability Index (FADI), FADI-Sport, and a self-report questionnaire of ankle function. Mechanically, talar position was quantified by measuring the distance from the anterior tibia to the anterior talus in the sagittal plane. Sensorimotor outcomes were the dynamic postural stability index and directional indices, which were calculated during a single-legged hop stabilization task. RESULTS Perceptual outcomes demonstrated diagnostic accuracy (range, 0.79-0.91), with 95% confidence intervals ranging from 0.65 to 1.00. Sensorimotor outcomes also were able to discriminate between copers and people with CAI but with less accuracy (range, 0.69-0.70), with 95% confidence intervals ranging from 0.37 to 0.86. The mechanical outcome demonstrated poor diagnostic accuracy (0.52). CONCLUSIONS The greatest diagnostic utility scores were achieved by the self-assessed disability questionnaires, which indicated that perceptual outcomes had the greatest ability to accurately predict people who became copers after their initial injuries. However, the diversity of outcome measures that discriminated between copers and people with CAI indicated that the causal mechanism of CAI is probably multifactorial.