The "impacts cause injury" hypothesis: Running in circles or making new strides?

Some of the earliest biomechanics research focused on running and the ground reaction forces generated with each step. Research in running gait accelerated in the 1970's as the growing popularity in running increased attention to the musculoskeletal injuries sustained by runners. Despite decades of high-quality research, running remains the most common cause of exercise-related musculoskeletal injuries and rates of overuse running-related injuries (RRI) have not appreciably declined since the research began. One leading area of running gait research focuses on discrete variables derived from the vertical ground reaction force, such as the vertical loading rate. Across sub-disciplines of running gait research, vertical loading rate is often discussed as the primary and undisputed variable associated with RRI despite only low to moderate evidence that retrospectively or prospectively injured runners generate greater vertical loading rates than uninjured counterparts. The central thesis of this review is that relying on vertical loading rate is insufficient to establish causal mechanisms for RRI etiology. To present this argument, this review examines the history of the 'impacts cause injury' hypothesis, including a historical look at ground reaction forces in human running and the research from which this hypothesis was generated. Additionally, a synthesis of studies that have tested the hypothesis is provided and recommendations for future research are discussed. Although it is premature to reject or support the 'impacts cause injury' hypothesis, new knowledge of biomechanical risk factors for RRI will remain concealed until research departs from the current path or adopts new approaches to previous paradigms.

Gender Differences in Lower Extremity Stiffness during a Single-Leg Landing Motion in Badminton

In general, at the same level of exercise, female athletes are three to six times more likely to injure an anterior cruciate ligament (ACL) than male athletes. Female athletes also had higher rates of ACL injury than males in a single-leg landing task after a backcourt backhand side overhead stroke in badminton. In many previous studies, stiffness of the musculoskeletal system in the lower limbs has been reported as a potential factor contributing to differences in ACL injury rates between genders. The purpose of this study was to describe the differences between genders in leg and knee stiffness in male and female athletes during a single-leg landing action after the backhand side overhead shot in the backcourt. Eight male athletes and eight female athletes participated in this test. Leg stiffness and knee stiffness were calculated separately for male and female athletes during the landing phase. The results showed that both absolute and normalized leg stiffness were lower in female athletes than in male athletes (p < 0.05). And both absolute and normalized knee stiffness were also lower than male athletes (p < 0.05). The low leg stiffness and knee stiffness demonstrated by females in this single-leg drop task compared to male athletes may indicate that females have lower dynamic leg stability than males during the drop, which may lead to hypermobility of the knee joint and may put females at a higher risk of injury in this high-risk maneuver for non-contact cruciate ligament injuries.

Comparison and analysis of the biomechanics of the lower limbs of female tennis players of different levels in foot-up serve

Purpose: The purpose of this study was to examine biomechanical performance of the foot-up serve (FUS) in female tennis players at different skill levels. Methods: FUS analysis was completed in the biomechanical laboratory by 32 female college tennis players at three different levels. During FUS, 3D-biomechanical data from tennis players' lower limbs were collected. One-way ANOVA was used to examine differences in kinematic and kinetic data between groups Results: Range of motion (ROM) of bilateral lower-limb joints revealed significant differences in kinematics performance during both the preparation and landing cushion phases (p < 0.05). During preparation, Level 3 was significantly longer than Level 2 (P-a = 0.042, P-b = 0.001, and P-c = 0.006). During the flight phase, significant differences between levels 1 and 3 (P-a:0.002) and levels 1 and 2 (P-c:0.000) were discovered (P-a:0.002 and P-c:0.000). There were significant height differences between levels 1 and 2 as well as between levels 1 and 3. (P-a = 0.001, P-c = 0.000). During serve preparation (P-c = 0.001) and landing, GRF's peak was significantly higher than level 3. (P-c:0.007). Significant differences were found between groups in the LLS preparation stage, with level 3 significantly higher than levels 1 and 2. (P-a = 0.000, P-b = 0.001, and P-c = 0.000); during landing, level 2 LLS was significantly higher than levels 1 and 3. (P-a = 0.000, P-b = 0.000, and P-c = 0.035). Conclusion: The range of motion of joints and the stiffness of the lower limbs have a significant impact on a tennis player's FUS performance. A larger of joint mobility and lower-limb stiffness promote better performance during the FUS preparation stage.

The Effect of Concussion History on Lower Extremity Injury Risk in College Athletes: A Systematic Review and Meta-Analysis

Introduction

Collegiate athletes who suffer a concussion may possess prolonged impairments even after clearance for return-to-participation, which may place them at an increased risk of lower extremity injury.

Objective

To conduct a systematic review and meta-analysis of studies examining risk of lower extremity musculoskeletal injury following a concussion in collegiate athletes.

Methods

A literature search was performed using the following databases: PubMed, CINAHL, SPORTDiscus. The following search terms were used to identify relevant articles, ["concussion" OR "brain injury" OR "mild traumatic brain injury" OR "mTBI"] AND ["lower extremity injury" OR "musculoskeletal injury"]. Articles were included if they were published between January 2000 and July 2021 and examined collegiate athletes' risk of sustaining a lower extremity musculoskeletal injury following a concussion. Methodological quality of included studies was performed with a modified Downs and Black Checklist. The primary outcome of interest was the risk of sustaining a lower extremity musculoskeletal injury following a concussion. A random effects meta-analysis was conducted in which a summative relative risk (RR) for sustaining a lower extremity injury in athletes with and without a history of concussion was calculated.

Results

Seven studies met the eligibility criteria to be included in the systematic review. There were 348 athletes in the concussion group and 482 control athletes in the included studies. Most of the studies were of good or excellent quality. Five of the seven studies were able to be included in the meta-analysis. College athletes who suffered a concussion possessed a 58% greater risk of sustaining a lower extremity musculoskeletal injury than those who did not have a history of a concussion (RR = 1.58[1.30, 1.93]).

Conclusions

Lower extremity injury risk is potentially increased in college athletes following a concussion compared to those without a history of a concussion. Further research is needed to investigate the mechanism behind this increased risk. Clinical assessments throughout the concussion return-to-play protocol may need to be improved in order to detect lingering impairments caused by concussions.

Level of Evidence

1.

Association Between Landing Error Scoring System (LESS) Items and the Incidence Rate of Lower Extremity Stress Fracture

Background:

Lower extremity stress fracture injuries are a major cause of morbidity in physically active populations. The ability to screen for modifiable risk factors associated with injury is critical in developing injury-prevention programs.

Purpose:

To determine if baseline Landing Error Scoring System (LESS) scores are associated with the incidence rate of lower extremity stress fracture.

Study Design:

Cohort study; Level of evidence, 2.

Methods:

A total of 1772 participants with no history of lower extremity stress fracture were included. At preinjury baseline, the authors conducted a lower extremity movement assessment during a jump-landing task using the LESS. Incident lower extremity stress fractures were identified during a 4-year follow-up period. Potential incident cases were reviewed by 2 sports medicine fellowship–trained orthopaedic surgeons blinded to baseline LESS data. Univariate and multivariable Poisson regression models were used to estimate the association between baseline total LESS scores, individual LESS items, and the incidence rate ratio (IRR) of lower extremity stress fracture.

Results:

A total of 94 incident lower extremity stress fractures were documented, for a 5.3% (95% CI, 4.3%-6.5%) cumulative incidence. The overall LESS score was associated with the incidence rate of lower extremity stress fracture. For every additional movement error documented at baseline, there was a 15% increase in the incidence rate of lower extremity stress fracture (IRR, 1.15 [95% CI, 1.02-1.31]; P = .025). In univariate analyses, ankle flexion, stance width, asymmetrical landing, and trunk flexion at initial contact, in addition to overall impression, were associated with the incidence rate of stress fracture. After controlling for sex and year of entry into the study cohort, participants who consistently landed flat-footed or heel-to-toe were 2.33 times (95% CI, 1.36-3.97; P = .002) more likely to sustain a lower extremity stress fracture. Similarly, participants who consistently demonstrated asymmetric landing at initial contact were 2.53 times (95% CI, 1.34-4.74; P = .004) more likely to sustain a stress fracture.

Conclusion:

Components of the LESS may be associated with increased lower extremity stress fracture risk and may be helpful in efficiently assessing high-risk lower extremity biomechanics in large groups.

Characterizing the Mechanical Stiffness of Passive-Dynamic Ankle-Foot Orthosis Struts

People with lower limb impairment can participate in activities such as running with the use of a passive-dynamic ankle-foot orthosis (PD-AFO). Specifically, the Intrepid Dynamic Exoskeletal Orthosis (IDEO) is a PD-AFO design that includes a carbon-fiber strut, which attaches posteriorly to a custom-fabricated tibial cuff and foot plate and acts in parallel with the impaired biological ankle joint to control sagittal and mediolateral motion, while allowing elastic energy storage and return during the stance phase of running. The strut stiffness affects the extent to which the orthosis keeps the impaired biological ankle in a neutral position by controling sagittal and mediolateral motion. The struts are currently manufactured to a thickness that corresponds with one of five stiffness categories (1 = least stiff, 5 = most stiff) and are prescribed to patients based on their body mass and activity level. However, the stiffness values of IDEO carbon-fiber struts have not been systematically determined, and these values can inform dynamic function and biomimetic PD-AFO prescription and design. The PD-AFO strut primarily deflects in the anterior direction (ankle dorsiflexion), and resists deflection in the posterior direction (ankle plantarflexion) during the stance phase of running. Thus, we constructed a custom apparatus and measured strut stiffness for 0.18 radians (10°) of anterior deflection and 0.09 radians (5°) of posterior deflection. We measured the applied moment and strut deflection to compute angular stiffness, the quotient of moment and angle. The strut moment-angle curves for anterior and posterior deflection were well characterized by a linear relationship. The strut stiffness values for categories 1–5 at 0.18 radians (10°) of anterior deflection were 0.73–1.74 kN·m/rad and at 0.09 radians (5°) of posterior deflection were 0.86–2.73 kN·m/rad. Since a PD-AFO strut acts in parallel with the impaired biological ankle, the strut and impaired biological ankle angular stiffness sum to equal total stiffness. Thus, strut stiffness directly affects total ankle joint stiffness, which in turn affects ankle motion and energy storage and return during running. Future research is planned to better understand how use of a running-specific PD-AFO with different strut stiffness affects the biomechanics and metabolic costs of running in people with lower limb impairment.

Effects of Foot-Core Training on Foot-Ankle Kinematics and Running Kinetics in Runners: Secondary Outcomes From a Randomized Controlled Trial

This study investigated the effectiveness of an 8-week foot-core exercise training program on foot-ankle kinematics during running and also on running kinetics (impact loads), with particular interest in biomechanical outcomes considered risk factors for running-related injuries in recreational runners. A single-blind, randomized, controlled trial was conducted with 87 recreational runners randomly allocated to either the control (CG) or intervention (IG) group and assessed at baseline and after 8 weeks. The IG underwent foot-core training 3 times/week, while the CG followed a placebo lower-limb stretching protocol. The participants ran on a force-instrumented treadmill at a self-selected speed while foot-segment motion was captured simultaneously with kinetic measurements. After the intervention, there were statistically significant changed in foot biomechanics, such as: IG participants strike the ground with a more inverted calcaneus and a less dorsiflexed midfoot than those in the CG; at midstance, ran with a less plantarflexed and more adducted forefoot and a more abducted hallux; and at push-off, ran with a less dorsiflexed midfoot and a less adducted and more dorsiflexed hallux. The IG runners also had significantly decreased medial longitudinal arch excursion (p = 0.024) and increased rearfoot inversion (p = 0.037). The 8-week foot-core exercise program had no effect on impact (p = 0.129) and breaking forces (p = 0.934) or on vertical loading rate (p = 0.537), but it was positively effective in changing foot-ankle kinematic patterns.”

Do harder midsoles facilitate propulsion and do softer midsoles increase shock attenuation during taking-off and landing of scissor jump?

To determine the influence of midsole hardness on ground reaction force (GRF) features during badminton scissor jump takeoff and landing and the interactive effect of midsole hardness with playing and nonplaying limbs, data were collected from badminton athletes who performed scissor jumps while wearing shoes with two levels of midsole hardness. Temporal-spatial and GRF variables were calculated. Measurements of the soft and hard midsole conditions for playing versus non-playing sides were compared using two-way repeated measure analyses of variance. The playing and non-playing limbs showed different GRF features while performing scissor jump. During takeoff, no significant differences between the soft and hard midsole conditions were identified for the jump height in any of the GRF variables. During landing, the cushioning capacity might be affected by harder midsole indicated by higher vertical impact peak (p = 0.008). Meanwhile, the longer time-to-vertical impact peak (p = 0.007) and the lower loading rate of the vertical impact peak (p = 0.013) may be plausible indicators for cushioning. Current study indicated the playing-limb consistently showed dominance on both the propulsion and shock attenuation behaviours during scissor jump and that, for the footwear selection between 62C and 68C midsoles, expectation would be more on effects on landing characteristics than on propulsion performance.

Relevance of Frequency-Domain Analyses to Relate Shoe Cushioning, Ground Impact Forces and Running Injury Risk: A Secondary Analysis of a Randomized Trial With 800+ Recreational Runners

Cushioning systems in running shoes are used assuming that ground impact forces relate to injury risk and that cushioning materials reduce these impact forces. In our recent trial, the more cushioned shoe version was associated with lower injury risk. However, vertical impact peak force was higher in participants with the Soft shoe version. The primary objective of this study was to investigate the effect of shoe cushioning on the time, magnitude and frequency characteristics of peak forces using frequency-domain analysis by comparing the two study groups from our recent trial (Hard and Soft shoe group, respectively). The secondary objective was to investigate if force characteristics are prospectively associated with the risk of running-related injury. This is a secondary analysis of a double-blinded randomized trial on shoe cushioning with a biomechanical running analysis at baseline and a 6-month follow-up on running exposure and injury. Participants (n = 848) were tested on an instrumented treadmill at their preferred running speed in their randomly allocated shoe condition. The vertical ground reaction force signal for each stance phase was decomposed into the frequency domain using the discrete Fourier transform. Both components were recomposed into the time domain using the inverse Fourier transform. An analysis of variance was used to compare force characteristics between the two study groups. Cox regression analysis was used to investigate the association between force characteristics and injury risk. Participants using the Soft shoes displayed lower impact peak force (p < 0.001, d = 0.23), longer time to peak force (p < 0.001, d = 0.25), and lower average loading rate (p < 0.001, d = 0.18) of the high frequency signal compared to those using the Hard shoes. Participants with low average and instantaneous loading rate of the high frequency signal had lower injury risk [Sub hazard rate ratio (SHR) = 0.49 and 0.55; 95% Confidence Interval (CI) = 0.25–0.97 and 0.30–0.99, respectively], and those with early occurrence of impact peak force (high frequency signal) had greater injury risk (SHR = 1.60; 95% CI = 1.05–2.53). Our findings may explain the protective effect of the Soft shoe version previously observed. The present study also demonstrates that frequency-domain analyses may provide clinically relevant impact force characteristics.

Clinical Trial Registration:https://clinicaltrials.gov/, identifier: 9NCT03115437.

Training Load Capacity, Cumulative Risk, and Bone Stress Injuries: A Narrative Review of a Holistic Approach

Bone stress injuries (BSIs) are a common orthopedic injury with short-term, and potentially long-term, effects. Training load capacity, influenced by risk factors, plays a critical role in the occurrence of BSIs. Many factors determine how one's body responds to repetitive loads that have the potential to increase the risk of a BSI. As a scientific community, we have identified numerous isolated BSI risk factors. However, we have not adequately analyzed the integrative, holistic, and cumulative nature of the risk factors, which is essential to determine an individual's specific capacity. In this narrative review, we advocate for a personalized approach to monitor training load so that individuals can optimize their health and performance. We define “cumulative risk profile” as a subjective clinical determination of the number of risk factors with thoughtful consideration of their interaction and propose that athletes have their own cumulative risk profile that influences their capacity to withstand specific training loads. In our narrative review, we outline BSI risk factors, discuss the relationship between BSIs and training load, highlight the importance of individualizing training load, and emphasize the use of a holistic assessment as a training load guide.

Relationships between tibial acceleration and ground reaction force measures in the medial-lateral and anterior-posterior planes

Peak vertical tibial accelerations during running have shown strong correlations with vertical ground reaction force loading rates and some associations with injury. However, little attention has been given to tibial accelerations along the medial-lateral and anterior-posterior axes. Therefore, our purpose was to examine the correlation between peak tibial accelerations and ground reaction force loading rates in the medial-lateral and posterior directions. Eighteen recreational runners were recruited who ran with a rearfoot strike pattern (10 men/ 8 women, mean age (yrs) = 33 ± 11). Tibial accelerations and ground reaction forces were collected while participants ran on an instrumented treadmill at a self-selected speed. Correlations were developed for: a) peak medial and lateral accelerations with lateral and medial loading rates, respectively, b) peak anterior tibial accelerations and posterior loading rates. Significant correlations were found between tibial accelerations and loading rates in all planes. Peak medial tibial accelerations were correlated with lateral loading rates (R_s = 0.86, p < 0.001) and peak lateral tibial accelerations were correlated with peak medial loading rates (R_s = 0.91, p < 0.001). A lower correlation was found between anterior accelerations and posterior loading rates (R_s = 0.51, p = 0.030). Tibial accelerations in the medial-lateral plane seem to be a valid surrogate for the respective ground reaction force measures during running on a treadmill, explaining 74-83% of the variance in loading rates. However, with only 26% of the variance explained, the same may not be true for anterior tibial accelerations and posterior loading rates.

Multifactorial Determinants of Running Injury Locations in 550 Injured Recreational Runners

PURPOSE

Despite the health benefits of running, the prevalence of running-related injuries (RRI) remains high. The underlying risk factors between these injuries are still not well understood. Therefore, the aim of this study was to compare biomechanical, anthropometric, and demographic injury risk factors between different locations in injured recreational runners.

METHODS

In this retrospective case-control analysis, 550 injured runners (49.6% female) with a medically diagnosed RRI were included. All runners had undergone an instrumented treadmill analysis to determine habitual footstrike pattern, vertical instantaneous load rate, peak vertical ground reaction force (vGRF) and cadence. Injuries were classified by location according to a recent consensus statement. A logistic regression model was used to determine the association between the biomechanical parameters and RRI locations. Because injuries can be associated with age, sex, and body mass index, these variables were also entered into the logistic regression.

RESULTS

Strike pattern and peak vGRF were the only biomechanical variable distinguishing an injury from the group of injuries. A midfoot strike differentiated Achilles tendon injuries (odds ratio [OR], 2.27; 90% confidence interval [CI], 1.17-4.41) and a forefoot strike distinguished posterior lower leg injuries (OR, 2.59; 90% CI, 1.50-4.47) from the rest of the injured group. Peak vGRF was weakly associated with hip injuries (OR, 1.14; 90% CI, 1.05-1.24). Female sex was associated with injuries to the lower leg (OR, 2.65; 90% CI, 1.45-4.87) and hip/groin (OR, 2.22; 90% CI, 1.43-3.45). Male sex was associated with Achilles tendon injuries (OR, 1.923; 90% CI, 1.094-3.378).

CONCLUSIONS

Sex, foot strike pattern, and vGRF were the only factors that distinguished specific injury locations from the remaining injury locations.

Influence of Sport Type on Metatarsophalangeal and Ankle Joint Stiffness and Hopping Performance

While individual ankle and metatarsophalangeal joint stiffness is related to training intensity and sport performances, sport athletes may develop specific passive joint stiffness among the spectrum from endurance to powerful types of sports. The objective of this study examined whether marathon runners, basketball players, and other sports athletes would demonstrate distinct passive ankle and metatarsophalangeal joint stiffness as well as vertical stiffness. Fifteen marathon runners, nineteen basketball players, and seventeen other sports athletes performed both joint stiffness measurement and single-leg hopping tests. We used a computerized dynamometer to control foot alignment and speed for passive ankle and metatarsophalangeal joint stiffness measurements. We calculated vertical stiffness by body deceleration and body mass displacement during hopping on the force platform. One-way ANOVA was performed to identify the group differences. Bivariate correlation test was also performed among ankle, metatarsophalangeal, and vertical stiffness. The basketball group displayed 13% higher ankle passive stiffness than the other sports players group (P = 0.03). Metatarsophalangeal joint passive stiffness in sitting and standing positions was 23% higher in the basketball group than the runner and other sports athlete groups (P < 0.01). However, there was no significant group differences in metatarsophalangeal joint passive stiffness and vertical stiffness. Significant correlations among all stiffness variables were determined (P < 0.05). These findings indicate that ankle and metatarsophalangeal joint passive stiffness, rather than vertical leg stiffness, would be in relation to types of sports participation. Ankle and toe strengthening exercises could improve basketball players' performance and prevent injury.

Effects of body weight support and pedal stance width on joint loading during pinnacle trainer exercise

BACKGROUND

A pinnacle trainer is a stair climber that has a biplane exercise trajectory and an adjustable pedal stance width (PSW). A pinnacle trainer integrated with a body weight support (BWS) system can help overweight individuals or individuals with poor balance exercise safely by reducing excessive or improper joint loads, preventing training-related injuries. However, few studies have investigated the biomechanical features of the lower extremities during pinnacle trainer exercise with and without partial BWS for various PSWs.

RESEARCH QUESTION

We aimed to investigate the effects of partial BWS and PSW on the joint loading of the lower extremities during stepping on a pinnacle trainer.

METHODS

Seventeen healthy adults exercised on the pinnacle trainer with or without BWS using various PSWs. The joint resultant forces and joint moments of the lower extremities were calculated according to the kinematic and kinetic data measured via a motion capture system and force transducers on the pedals, respectively.

RESULTS

The joint resultant forces and joint moments of the lower extremities significantly decreased with increasing percentage of BWS. The internal knee adduction moment and internal hip abduction moment significantly increased with increasing PSW. For every kilogram of BWS, the joint loading of the lower extremities decreased by approximately 1% of the joint resultant forces of body weight during exercise with the pinnacle trainer.

SIGNIFICANCE

Exercise on the pinnacle trainer with partial BWS significantly reduced joint loading. Exercise with a wider pedal stance may be helpful for knee osteoarthritis rehabilitation as it produces greater internal hip abduction and internal knee adduction moments.

Bone geometry and lower extremity bone stress injuries in male runners

Bone stress injuries (BSI) are common among distance runners and research investigations examining risk factors for BSI among men are limited. Therefore, investigations are needed to determine if men with a history of BSI have skeletal properties that may heighten BSI incidence.

OBJECTIVES

To analyze differences in bone density, bone geometry, and estimates of bone strength in male runners with and without a BSI history.

DESIGN

Cross-sectional.

METHODS

We recruited 36 male distance runners ages 18-41 for this study. We used peripheral quantitative computed tomography (pQCT) to assess volumetric bone mineral density (vBMD, mg/mm³), bone geometry (total and cortical bone area, mm²), tibia robustness (total area/tibia length, mm) and estimates of bone strength (section modulus and polar strength-strain index, mm³) at 5 tibial sites.

RESULTS

After adjusting for age, the BSI group had more slender tibias (9%), lower stress strain indices (-16%), lower section moduli (-17%) and smaller total cross-sectional (-11%) and cortical areas (-12%) at the 66% site of the tibia compared with controls (P < 0.05 for all). Similar differences were found at all other measurement sites. After adjusting for body size, differences in bone outcomes remained significant at the 66% site.

CONCLUSIONS

These results indicate that men with a history of BSI have lower estimated bending strength compared to controls because of narrower tibias. However, differences are largely attenuated in the distal ½ of the tibia after adjusting for body size. Thus, smaller tibia size, particularly at the mid-diaphysis, may be an important indicator for BSI incidence.

Effect of different loading conditions on running mechanics at different velocities

Weighted vests are widely used to improve running economy and performance. However, it is not well-studied how running mechanics are adapted to counteract the higher peak vertical ground reaction forces (Fpeak) while running with such a device. Therefore, the present study aimed to investigate the effects of different loading conditions on running mechanics at different velocities. Thirteen subjects participated in two separate sessions one week apart. In the first session, maximal aerobic speed (MAS) was determined through a maximal incremental running test while in the second session, they were instructed to run during one minute under different loading (0%, +10% and +20% of body mass [BM]) and velocity (60%, 80% and 100% of MAS) conditions in a random order. Spatiotemporal data were recorded and then running mechanics modelled using the spring-mass model. The main results indicated that vertical and leg stiffness (Kvert and Kleg, respectively) were increased (P < .001) as velocity increased but remained unaltered (P > .05) when load was changed. At the same time, alterations of the running kinematics were observed such as longer contact times, reduced flight times, stride frequencies and step lengths, as well as an increase of the centre of mass dynamics. Based on these results it is assumed that runners maintain a certain stiffness level for each velocity despite different loading conditions. As a consequence, Fpeak increases and this probably causes spatiotemporal adjustments in the movement kinematics.

Accelerometer-based prediction of running injury in National Collegiate Athletic Association track athletes

Running-related injuries (RRI) may result from accumulated microtrauma caused by combinations of high load magnitudes (vertical ground reaction forces; vGRFs) and numbers (strides). Yet relationships between vGRF and RRI remain unclear - potentially because previous research has largely been constrained to collecting vGRFs in laboratory settings and ignoring relationships between RRI and stride number. In this preliminary proof-of-concept study, we addressed these constraints: Over a 60-day period, each time collegiate athletes (n = 9) ran they wore a hip-mounted activity monitor that collected accelerations throughout the entire run. Accelerations were used to estimate peak vGRF, number of strides, and weighted cumulative loading (sum of peak vGRFs weighted to the 9th power) across the entirety of each run. Runners also reported their post-training pain/fatigue and any RRI that prevented training. Across 419 runs and >2.1 million strides, injured (n = 3) and uninjured (n = 6) participants did not report significantly different pain/fatigue (p = 0.56) or mean number of strides per run (p = 0.91). Injured participants did, however, have significantly greater peak vGRFs (p = 0.01) and weighted cumulative loading per run (p < 0.01). Results from this small but extensively studied sample of elite runners demonstrate that loading profiles (load magnitude-number combinations) quantified with activity monitors can provide valuable information that may prove essential for: (1) testing hypotheses regarding overuse injury mechanisms, (2) developing injury-prediction models, and (3) designing and adjusting athlete- and loading-specific training programs and feedback.

The effect of knee flexor and extensor fatigue on shock absorption during cutting movements after a jump landing

BACKGROUND

Sporting situations include instances of continuous and/or integrated movements. However, the effect of fatigue on the performance of these movements remains unclear.

PURPOSE

To investigate the effect of knee flexor and extensor fatigue on the shock absorption strategy of the lower limb during cutting movements performed after jump landings.

METHODS

Twenty-four healthy participants performed cutting movements following jump landings from two heights - 30cm and 40cm - and under three levels of lower limb fatigue: pre-fatigue (100% peak knee extension torque), and post-fatigue 50% (post-50%) and 30% (post-30%) peak knee extension torque. Fatigue was induced by repeated isokinetic flexion/extension of the knee (60°/s).

RESULTS

Compared to the pre-fatigue condition, power and work at the knee joint decreased under both post-50% and post-30% conditions (P<0.001), while the work performed by the ankle (P<0.001) increased significantly. An increase in height from 30cm to 40cm was associated with an increase in the range of motion of the ankle (P<0.001) and knee (P=0.022), peak vertical ground reaction force (P<0.001), rate of loading (P<0.001), knee stiffness (P=0.026) and peak power of the knee (P<0.001), as well as the work performed by the knee (P<0.001) and hip (P<0.001) joints.

CONCLUSIONS

Under substantial muscle fatigue the proportion of shock absorption contributed by the knee for cutting movements performed after jump landings from a height of 40cm decreased; there was an adaptive increase in the contribution by the ankle.

The relationship between lower body stiffness and injury incidence in female netballers

The aim of this study was to provide contemporary information on injury rates in an elite and sub-elite netball population and to explore the relationship between lower body stiffness and lower body injuries. One elite and two sub-elite teams of female netballers (n = 29) performed the vertical hop test to assess active lower body stiffness (K_vert) and myometry to assess quasi-static stiffness. Lower body injuries were monitored via self-reporting and liaison with physiotherapists. Twelve lower body non-contact injuries were sustained by 10 players, equating to 11.29 lower body injuries per 1,000 exposure hours. The most commonly injured sites were the calf (33%) and ankle (25%). No significant differences between K_vert of injured and non-injured players were reported, however, injured elite players recorded significantly higher season mean quasi-static stiffness in the soleus (p = 0.037) and Achilles (p = 0.004) than non-injured elite players. Elite and sub-elite netball players recorded a higher injury incidence than previous reports of injuries in recreational netballers. Within the constraints of the study, relatively high stiffness of the soleus and Achilles appears to be related to lower body non-contact injury incidence in female netballers, particularly at the elite level. These results provide a basis for development of injury prevention strategies.

Bone strength estimates relative to vertical ground reaction force discriminates women runners with stress fracture history

PURPOSE

To determine differences in bone geometry, estimates of bone strength, muscle size and bone strength relative to load, in women runners with and without a history of stress fracture.

METHODS

We recruited 32 competitive distance runners aged 18-35, with (SFX, n=16) or without (NSFX, n=16) a history of stress fracture for this case-control study. Peripheral quantitative computed tomography (pQCT) was used to assess volumetric bone mineral density (vBMD, mg/mm³), total (ToA) and cortical (CtA) bone areas (mm²), and estimated compressive bone strength (bone strength index; BSI, mg/mm⁴) at the distal tibia. ToA, CtA, cortical vBMD, and estimated strength (section modulus; Zp, mm³ and strength strain index; SSIp, mm³) were measured at six cortical sites along the tibia. Mean active peak vertical (pkZ) ground reaction forces (GRFs), assessed from a fatigue run on an instrumented treadmill, were used in conjunction with pQCT measurements to estimate bone strength relative to load (mm²/N∗kg^-1) at all cortical sites.

RESULTS

SSIp and Zp were 9-11% lower in the SFX group at mid-shaft of the tibia, while ToA and vBMD did not differ between groups at any measurement site. The SFX group had 11-17% lower bone strength relative to mean pkZ GRFs (p<0.05).

CONCLUSION

These findings indicate that estimated bone strength at the mid-tibia and mean pkZ GRFs are lower in runners with a history of stress fracture. Bone strength relative to load is also lower in this same region suggesting that strength deficits in the middle 1/3 of the tibia and altered gait biomechanics may predispose an individual to stress fracture.

Is passive metatarsophalangeal joint stiffness related to leg stiffness, vertical stiffness and running economy during sub-maximal running?

This study examined whether passive metatarsophalangeal joints (MPJ) stiffness was associated with leg stiffness (Kleg) vertical stiffness (Kvert) and running economy (RE) during sub-maximal running. Nine male experienced runners underwent passive MPJ stiffness measurements in standing and sitting positions followed by sub-maximal running on an instrumented treadmill. With the individual foot position properly aligned, the MPJ passive stiffness in both sitting (MPJsit) and standing positions (MPJstand) were measured with a computerized dynamometer. Data were collected at a running speed of 2.78m/s, representing a stabilized level of energy expenditure. Pedar pressure insole was used to determine the contact time (tc) and peak reaction force for the calculation of Kleg and Kvert. A respiratory gas analysis system was used to estimate the RE. Bivariate correlation test was performed to examine the correlation among MPJ stiffness, contact time, Kleg, Kvert, and RE. The results showed that MPJsit and MPJstand were inversely correlated with RE (p=0.04, r=-0.68 to -0.69), suggesting that stiffer MPJ improves RE. In addition, MPJsit was correlated positively with Kleg (p<0.01, r=0.87),Kvert (p=0.03, r=0.70) but inversely with tc (p=0.02, r=-0.76), while MPJstand was correlated positively with the Kvert (p=0.02, r=0.77). These findings suggested that strength of toe plantar flexors provides stability and agility in the stance phase for more effective and faster forward movement.

Biomechanical response to ankle-foot orthosis stiffness during running

BACKGROUND

The Intrepid Dynamic Exoskeletal Orthosis (IDEO) is an ankle-foot orthosis developed to address the high rates of delayed amputation in the military. Its use has enabled many wounded Service Members to run again. During running, stiffness is thought to influence an orthosis' energy storage and return mechanical properties. This study examined the effect of orthosis stiffness on running biomechanics in patients with lower limb impairments who had undergone unilateral limb salvage.

METHODS

Ten patients with lower limb impairments underwent gait analysis at a self-selected running velocity. 1. Nominal (clinically-prescribed), 2. Stiff (20% stiffer than nominal), and 3. Compliant (20% less stiff than nominal) ankle-foot orthosis stiffnesses were tested.

FINDINGS

Ankle joint stiffness was greatest in the stiffest strut and lowest in the compliant strut, however ankle mechanical work remained unchanged. Speed, stride length, cycle time, joint angles, moments, powers, and ground reaction forces were not significantly different among stiffness conditions. Ankle joint kinematics and ankle, knee and hip kinetics were different between limbs. Ankle power, in particular, was lower in the injured limb.

INTERPRETATION

Ankle-foot orthosis stiffness affected ankle joint stiffness but did not influence other biomechanical parameters of running in individuals with unilateral limb salvage. Foot strike asymmetries may have influenced the kinetics of running. Therefore, a range of stiffness may be clinically appropriate when prescribing ankle-foot orthoses for active individuals with limb salvage.

Análise isocinética e cinética de corredores e triatletas com e sem histórico de fratura por estresse

INTRODUÇÃO: A associação da fadiga muscular com o aumento da força vertical de reação do solo representa risco de fratura por estresse de tíbia em esportes como a corrida de longa distância e o triatlo. Objetivo: Analisar e comparar parâmetros do componente vertical das forças de reação do solo e parâmetros musculares isocinéticos da flexão plantar (FP) e dorsiflexão (DF) do tornozelo entre grupos de corredores de longa distância e triatletas com e sem histórico de fratura por estresse de tíbia.MÉTODOS: Setenta e cinco atletas de corrida de longa distância e triatletas do sexo masculino, com média de idade de 30,26 ± 6,51 anos foram divididos de acordo com a história pregressa de fratura por estresse de tíbia em: grupo fratura (GF), composto por 12 indivíduos com história de fratura por estresse da tíbia, e grupo não-fratura (GNF), composto por 37 indivíduos sem história de fratura por estresse de tíbia. Os parâmetros cinéticos foram medidos durante a corrida por meio de uma plataforma de força AMTI, e os parâmetros isocinéticos por meio de dinamômetro isocinético Biodex (System 3).RESULTADOS: Para todas as variáveis isocinéticas e cinéticas, não houve diferenças entre GF e GNF.CONCLUSÃO: Ainda que não se tenha identificado uma diferença de desempenho entre os grupos estudados, o perfil cinético (impacto) e isocinético (atividade muscular) mostra que o treinamento da corrida com déficits em cuidados com a condição muscular e o controle de fatores extrínsecos pode criar uma situação de risco de ocorrência de fraturas por estresse.

Sex Differences in Limb and Joint Stiffness in Recreational Runners

Purpose. Female runners are known to be at greater risk from chronic running injuries than age-matched males, although the exact mechanisms are often poorly understood. The aim of the current investigation was to determine if female recreational runners exhibit distinct limb and joint stiffness characteristics in relation to their male counterparts. Methods. Fourteen male and fourteen female runners ran over a force platform at 4.0 m · s

Differences in distal lower extremity tissue masses and mass ratios exist in athletes of sports involving repetitive impacts

This study aimed to examine the effects of sex and sport on the tissue composition of the distal lower extremity of varsity athletes, in sports that involve repetitive-impact loading patterns. Fat mass, lean mass, bone mineral content and wobbling mass were predicted for the leg and leg + foot segments of varsity basketball, cross-country, soccer and volleyball athletes. The absolute masses were normalised to body mass, and also expressed relative to each other as ratios. Females and males differed on most normalised tissue masses and ratios by 11-101%. Characteristic differences were found in the normalised tissue masses across sports, with the lowest and highest values displayed by cross-country and volleyball (female)/basketball (male) athletes, respectively. Conversely, cross-country athletes had the highest wobbling mass:bone mineral content and lean mass:bone mineral content ratios for females by 10% and 16%, respectively. The differences between sports may be explained in part by different impact loading patterns characteristic of each sport. Tissue mass ratio differences between sports may suggest that the ratios of soft to rigid tissues are optimised by the body in response to typical loading patterns, and may therefore be useful in investigations of distal lower extremity injury mechanisms in athletes.

The effects of load carriage and muscle fatigue on lower-extremity joint mechanics

Military personnel are commonly afflicted by lower-extremity overuse injuries. Load carriage and muscular fatigue are major stressors during military basic training.

PURPOSE

To examine effects of load carriage and muscular fatigue on lower-extremity joint mechanics during walking.

METHOD

Eighteen men performed the following tasks: unloaded walking, walking with a 32-kg load, fatigued walking with a 32-kg load, and fatigued walking. After the second walking task, muscle fatigue was elicited through a fatiguing protocol consisting of metered step-ups and heel raises with a 16-kg load. Each walking task was performed at 1.67 m x s(-1) for 5 min. Walking movement was tracked by a VICON motion capture system at 120 Hz. Ground reaction forces were collected by a tandem force instrumented treadmill (AMTI) at 2,400 Hz. Lower-extremity joint mechanics were calculated in Visual 3D.

RESULTS

There was no interaction between load carriage and fatigue on lower-extremity joint mechanics (p > .05). Both load carriage and fatigue led to pronounced alterations of lower-extremity joint mechanics (p < .05). Load carriage resulted in increases of pelvis anterior tilt, hip and knee flexion at heel contact, and increases of hip, knee, and ankle joint moments and powers during weight acceptance. Muscle fatigue led to decreases of ankle dorsiflexion at heel contact, dorsiflexor moment, and joint power at weight acceptance. In addition, muscle fatigue increased demand for hip extensor moment and power at weight acceptance.

CONCLUSION

Statistically significant changes in lower-extremity joint mechanics during loaded and fatigued walking may expose military personnel to increased risk for overuse injuries.

Changes in biomechanical properties during drop jumps of incremental height

The purpose of this study was to investigate changing biomechanical properties with increasing drop jump height. Sixteen physically active college students participated in this study and performed drop jumps from heights of 20, 30, 40, 50, and 60 cm (DJ20-DJ60). Kinematic and kinetic data were collected using 11 Eagle cameras and 2 force platforms. Data pertaining to the dominant leg for each of 3 trials for each drop height were recorded and analyzed. Statistical comparisons of vertical ground reaction force (vGRF), impulse, moment, power, work, and stiffness were made between different drop jump heights. The peak vGRF of the dominant leg exceeded 3 times the body weight during DJ50 and DJ60; these values were significantly greater than those for DJ20, DJ30, and DJ40 (all p < 0.004). The height jumped during DJ60 was significantly less than that during DJ20 and DJ30 (both p = 0.010). Both the landing impulse and total impulse during the contact phase were significantly different between each drop height (all p < 0.036) and significantly increased with drop height. There were no significant differences in the takeoff impulse. Peak and mean power absorption and negative work at the knee and ankle joints during DJ40, DJ50, and DJ60 were significantly greater than those during DJ20 and DJ30 (all p < 0.049). Leg, knee, and ankle stiffness during DJ60 were significantly less than during DJ20, DJ30, and DJ40 (all p < 0.037). The results demonstrated that drop jumps from heights >40 cm offered no advantages in terms of mechanical efficiency (SSC power output) and stiffness. Drop jumps from heights in excess of 60 cm are not recommended because of the lack of biomechanical efficiency and the potentially increased risk of injury.

Sagittal plane bending moments acting on the lower leg during running

Sagittal bending moments acting on the lower leg during running may play a role in tibial stress fracture development. The purpose of this study was to evaluate these moments at nine equidistant points along the length of the lower leg (10% point-90% point) during running. Kinematic and ground reaction force data were collected for 20 male runners, who each performed 10 running trials. Inverse dynamics and musculoskeletal modelling techniques were used to estimate sagittal bending moments due to reaction forces and muscle contraction. The muscle moment was typically positive during stance, except at the most proximal location (10% point) on the lower leg. The reaction moment was predominantly negative throughout stance and greater in magnitude than the muscle moment. Hence, the net sagittal bending moment acting on the lower leg was principally negative (indicating tensile loads on the posterior tibia). Peak moments typically occurred around mid-stance, and were greater in magnitude at the distal, compared with proximal, lower leg. For example, the peak reaction moment at the most distal point was -9.61+ or - 2.07%Bw.Ht., and -2.73 + or - 1.18%Bw.Ht. at the most proximal point. These data suggest that tensile loads on the posterior tibia are likely to be higher toward the distal end of the bone. This finding may explain the higher incidence of stress fracture in the distal aspect of the tibia, observed by some authors. Stress fracture susceptibility will also be influenced by bone strength and this should also be accounted for in future studies.

Section modulus is the optimum geometric predictor for stress fractures and medial tibial stress syndrome in both male and female athletes

BACKGROUND

Various tibial dimensions and geometric parameters have been linked to stress fractures in athletes and military recruits, but many mechanical parameters have still not been investigated.

HYPOTHESES

Sedentary people, athletes with medial tibial stress syndrome, and athletes with stress fractures have smaller tibial geometric dimensions and parameters than do uninjured athletes.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Using a total of 88 subjects, male and female patients with either a tibial stress fracture or medial tibial stress syndrome were compared with both uninjured aerobically active controls and uninjured sedentary controls. Tibial scout radiographs and cross-sectional computed tomography images of all subjects were scanned at the junction of the midthird and distal third of the tibia. Tibial dimensions were measured directly from the films; other parameters were calculated numerically.

RESULTS

Uninjured exercising men have a greater tibial cortical cross-sectional area than do their sedentary and injured counterparts, resulting in a greater value of some other cross-sectional geometric parameters, particularly the section modulus. However, for women, the cross-sectional areas are either not different or only marginally different, and there are few tibial dimensions or geometric parameters that distinguish the uninjured exercisers from the sedentary and injured subjects. In women, the main difference between the groups was the distribution of cortical bone about the centroid as a result of the different values of section modulus. Last, medial tibial stress syndrome subjects had smaller tibial cross-sectional dimensions than did their uninjured exercising counterparts, suggesting that medial tibial stress syndrome is not just a soft-tissue injury but also a bony injury.

CONCLUSION

The results show that in men, the cross-sectional area and the section modulus are the key parameters in the tibia to distinguish exercise and injury status, whereas for women, it is the section modulus only.

The role of foot pronation in the development of femoral and tibial stress fractures: a prospective biomechanical study

OBJECTIVE

To examine whether dynamic parameters of foot pronation are risk factors for the development of stress fractures of the femur and tibia.

DESIGN

Observational prospective study.

SETTING

Infantry basic training course.

PARTICIPANTS

473 recruits evaluated for stress fractures of the femur and tibia every 2 weeks during 14 weeks of infantry basic training. The final analysis included 405 recruits.

ASSESSMENT OF RISK FACTORS

Two weeks before commencement of training, the recruits were evaluated during treadmill walking for their subtalar joint kinematics. Five independent variables were measured bilaterally: maximal pronation angle during the stance, pronation range of motion, time from heel strike to maximum pronation, pronation mean angular velocity, and time to maximum pronation as a percent of the total stance time.

MAIN OUTCOME MEASUREMENTS

Stress fractures of the femur and tibia. These were considered positive only when proven by imaging.

RESULTS

Ten percent of the participants were diagnosed with stress fractures of the femur and tibia. Recruits with longer duration of foot pronation had reduced odds ratio to develop this injury.

CONCLUSIONS AND CLINICAL RELEVANCE

Longer duration of foot pronation may have a protective effect from stress fractures of the femur and tibia. This finding may promote the understanding of stress fracture pathomechanism, assist in the identification of subjects with increased risk who need augmented monitoring throughout training, and assist in future planning of impact reducing aids.

Comparison of static and dynamic biomechanical measures in military recruits with and without a history of third metatarsal stress fracture

BACKGROUND

For Royal Marine recruits in training, the third metatarsal is the most common site for stress fracture. Previous evidence regarding biomechanical factors contributing to metatarsal stress fracture development is conflicting, possibly due to the lack of differentiation between the metatarsals. The present retrospective study compares static anatomical characteristics and dynamic biomechanical variables for Royal Marine recruits with and without a history of third metatarsal stress fracture.

METHODS

Ten Royal Marine recruits with a history of third metatarsal stress fracture were compared with control subjects with no previous stress fracture occurrence. Selected static anatomical variables were measured to describe the ankle and subtalar joints. Peak ankle dorsi-flexion and rearfoot eversion were measured during running. In addition, peak vertical and horizontal ground reaction force variables were compared for the two study groups.

FINDINGS

No significant differences in static anatomical variables were identified between study groups. During running, peak rearfoot eversion was found to occur significantly earlier for the stress fracture group than for their matched controls, suggesting an increase in time spent loading the forefoot. The peak applied resultant horizontal force during the braking phase was directed significantly more laterally for the stress fracture group. In addition, the peak magnitude of resultant horizontal force applied during the propulsion phase was significantly lower for the stress fracture subjects.

INTERPRETATION

The findings of this study highlight the importance of including dynamic biomechanical data when exploring variables associated with the development of third metatarsal stress fracture and indicate that successful interventions to reduce the incidence of this injury are likely to focus on forefoot function during braking and propulsion.

Plantar feedback contributes to the regulation of leg stiffness

BACKGROUND

Running and hopping involve moving in a bouncing fashion during which the limbs behave as springs. The ability to alter the stiffness of these leg springs is essential to maintaining an efficient gait. Since the plantar surface of the foot is the only part of the body to encounter the ground during bipedal locomotion, it would seem logical that some aspect of the neurological functioning of the foot is responsible for transmission of information about the surface characteristics to the central nervous system, resulting in changes in leg stiffness.

METHODS

Ten subjects (9 males, 1 female) participated in this experiment. Lidocaine was injected inferior and posterior to the lateral malleolus in order to achieve tibial nerve block at the level of the ankle. Subjects hopped at 2.2 Hz on a force plate while data were collected at 1000 Hz. Data were analyzed for peak force and leg stiffness and compared using a repeated measures ANOVA.

FINDINGS

Tactile sensation, deep pressure sensation, and abductor hallucis activity displayed significant decreases following the injection, as did postural stability. Subjects demonstrated a significantly decreased leg stiffness after the nerve block (P<.01).

INTERPRETATION

Plantar sensation has an effect on regulating leg mechanics in hopping. A loss of sensation in this region can exert a significant impact on the properties of the leg in gait, and future research should determine the specific pathways by which plantar feedback exerts this effect.

Ground Reaction Forces and Bone Parameters in Females with Tibial Stress Fracture

PURPOSE

Tibial stress fracture is a common overuse running injury that results from the interplay of repetitive mechanical loading and bone strength. This research project aimed to determine whether female runners with a history of tibial stress fracture (TSF) differ in ground reaction force (GRF) parameters during running, regional bone density, and tibial bone geometry from those who have never sustained a stress fracture (NSF).

METHODS

Thirty-six female running athletes (13 TSF; 23 NSF) ranging in age from 18 to 44 yr were recruited for this cross-sectional study. The groups were well matched for demographic, training, and menstrual parameters. A force platform measured selected GRF parameters (peak and time to peak for vertical impact and active forces, and horizontal braking and propulsive forces) during overground running at 4.0 m.s.(-1). Lumbar spine, proximal femur, and distal tibial bone mineral density were assessed by dual energy x-ray absorptiometry. Tibial bone geometry (cross-sectional dimensions and areas, and second moments of area) was calculated from a computerized tomography scan at the junction of the middle and distal thirds.

RESULTS

There were no significant differences between the groups for any of the GRF, bone density, or tibial bone geometric parameters (P > 0.05). Both TSF and NSF subjects had bone density levels that were average or above average compared with a young adult reference range. Factor analysis followed by discriminant function analysis did not find any combinations of variables that differentiated between TSF and NSF groups.

CONCLUSION

These findings do not support a role for GRF, bone density, or tibial bone geometry in the development of tibial stress fractures, suggesting that other risk factors were more important in this cohort of female runners.

Lower extremity stiffness: implications for performance and injury

BACKGROUND

Lower extremity stiffness is thought to be an important factor in musculoskeletal performance. However, too little or too much stiffness is believed to increase the risk of musculoskeletal injury.

PURPOSE

To provide a current update of the lower extremity stiffness literature as it pertains to both performance and injury.

SUMMARY

It appears that increased stiffness is beneficial to performance. As well it appears that there may be an optimal amount of stiffness that allows for injury-free performance. There is some evidence that increased stiffness may be related to bony injuries and decreased stiffness may be associated with soft tissue injuries. Further investigations should evaluate the relationship between stiffness and injury prospectively. Initial reports suggest that stiffness can be modified in response to the external environment or verbal cues.

RELEVANCE

A greater understanding of the role of stiffness in both performance and injury will provide a stronger foundation for the development of optimal training intervention programs.

Effect of Strike Pattern and Orthotic Intervention on Tibial Shock during Running

The main purpose of this study was to investigate the effects of both strike pattern (forefoot vs. rearfoot strike pattern) and orthotic intervention on shock to the lower extremity. Semi-rigid orthotic devices were manufactured for 15 injury-free recreational runners. Tibial accelerometry, ground reaction force, and 3D kinematic data were collected on their right leg in four conditions: forefoot strike (FFS) and rearfoot strike (RFS) with and without orthotics. Two-way repeated-measures analysis of variance tests were used to assess the effects of strike pattern and orthotic intervention on tibial acceleration; angular excursions of the ankle and knee; ground reaction force (GRF) vertical and anteroposterior peaks and load rates; and ankle, knee, and leg stiffness. There was a significant increase in tibial acceleration for the FFS pattern compared to the RFS pattern. This may be explained in part by the significantly greater peak vertical GRF, peak anteroposterior GRF, anteroposterior GRF load rates, knee stiffness, and leg stiffness found in the FFS pattern compared to the RFS pattern. Tibial acceleration and rearfoot eversion excursions were similar between the orthotic and no-orthotic conditions. Knee flexion excursion and average GRF vertical load rates were significantly decreased while dorsiflexion excursion and knee stiffness were significantly increased in the orthotic condition. No significant interactions were found between strike pattern and orthotic condition for any variables assessed.

Flexural wave propagation velocity and bone mineral density in females with and without tibial bone stress injuries

STUDY DESIGN

Case-control nonexperimental design.

OBJECTIVES

To compare flexural wave propagation velocity (FWPV) and tibial bone mineral density (BMD) in women with and without tibial bone stress injuries (BSIs).

BACKGROUND

Physical therapists, particularly in military and sports medicine settings, routinely diagnose and manage stress fractures or bone stress injuries. Improved methods of preparticipation quantification of tibial strength may provide markers of BSI risk and thus potentially reduce morbidity.

METHODS AND MEASURES

Bone mineral density, FWPV, bone geometry, and historical variables were collected from 14 subjects diagnosed with tibial BSIs and 14 age-matched controls; all 28 were undergoing military training.

RESULTS

No difference was found between groups in FWPV and tibial BMD when analyzed with t tests (post hoc power = 0.89 and 0.81, respectively). Furthermore, no difference was found in tibial length, tibial width, femoral neck BMD, and lumbar spine BMD among the groups. There were no differences between the 2 groups in smoking history, birth control pill use, and onset of menarche. Finally, sensitivity and positive likelihood ratios for FWPV (0.14 and 0.63), tibial BMD (0.0 and 0.0), and lumbar BMD (0.18 and 2.0) were low, while specificity was high (0.77, 0.93, and 0.91, respectively).

CONCLUSION

Current bone analysis devices and methods may not be sensitive enough to detect differences in tibial material and structure; local stresses on bone may be more important in the development of BSIs than the overall structural stiffness.

The oral contraceptive pill: a revolution for sportswomen?

OBJECTIVES

To determine the effects of the oral contraceptive pill (OCP) on skeletal health, soft tissue injury, and performance in female athletes.

METHODS

A literature review was performed using literature retrieval methods to locate relevant studies.

RESULTS

Most female athletes primarily choose to use the OCP for contraceptive purposes, but cycle manipulation and control of premenstrual symptoms are secondary advantages of its use. The effect of the OCP on bone density in normally menstruating women is unclear, with some studies reporting no effect, others a positive effect, and some even a negative effect. The OCP is often prescribed for the treatment of menstrual disturbances in female athletes, and improvements in bone density may result. Whether the OCP influences the risk of stress fracture and soft tissue injuries is not clear from research to date. Effects of the OCP on performance are particularly relevant for elite sportswomen. Although a reduction in Vo2MAX has been reported in some studies, this may not necessarily translate to impaired performance in the field. Moreover, some studies claim that the OCP may well enhance performance by reducing premenstrual symptoms and menstrual blood loss. A fear of weight gain with the use of the OCP is not well founded, as population studies report no effect on weight, particularly with the lower dose pills currently available.

CONCLUSIONS

Overall, the advantages of the pill for sportswomen would appear to outweigh any potential disadvantages. Nevertheless, there is individual variation in response to the OCP and these should be taken into account and monitored in the clinical situation. Women should be counselled as to the range of potential benefits and disadvantages in order to make an informed decision based on individual circumstances.