Joint movements associated with minimum toe clearance variability in older adults during level overground walking.

BACKGROUND: Approximately one-third of falls are caused by the swing foot contacting an object or the ground, resulting in a trip. The increased incidence of trip-related falls among older adults may be explained by greater within-person minimum toe clearance (MTC) variability. RESEARCH QUESTION: Will kinematic variability at any of the 6 major joints in the lower limbs, individually or in combination, be associated with MTC variability? METHODS: This cross-sectional study investigated whether single or multiple joint movements best explained MTC variability in older adults. Twenty healthy older adults (7 males, 13 females; mean age = 71.3 ±â€¯7.2 years) were recruited. Participants were fitted with a modified Cleveland Clinic marker set and walked for 50 trials at self-selected speeds over a 7-meter walkway (with a rest at 25 trials) while 6 infrared cameras recorded kinematics. RESULTS: Seven joint movements were evaluated, and swing hip flexion-extension variability was the only joint movement significantly associated with MTC variability (r = 0.577, p = 0.008) and explained 29.6% (adjusted R2) of the variance of MTC variability in older adults (F (1, 18) = 8.897, p = 0.008). SIGNIFICANCE: Identifying the joint movement/s associated with inconsistencies in toe clearance will improve our understanding of endpoint control in older adults and may lead to the development of effective trip prevention strategies.

Alteration of ankle kinematics and muscle activity during heel contact when walking with external loading.

PURPOSE: The risk of recurrent ankle sprains could be reduced if the ankle joint is positioned in a more closed pack position (eversion and dorsiflexion) with enhanced co-activation of Tibialis Anterior (TA) and Peroneus Longus (PL) around heel contact in walking. We examined whether such alteration can be induced by augmenting ankle position error in the inversion and plantarflexion directions. METHODS: Fifteen young, healthy subjects participated in this study. They walked on a treadmill while a light weight was affixed to the dorsal-lateral side of the test foot to create afferent error signals in the inversion and plantarflexion directions. We recorded and analyzed subjects' ankle kinematics and electromyographic (EMG) activity of TA and PL before (baseline), during (adaptation), and after (post adaptation) walking with the weight. Our analyses focused on 30 ms before and after heel contact where ankle sprains are most likely to occur. RESULTS: Subjects increased ankle eversion before and after heel contact during the adaptation period. This increase carried over to the post adaptation period following removal of the weight. The weight also induced an increase in the TA activity before heel contact during late adaptation, although this increase did not carry over to the post adaptation period. No significant changes were observed in ankle dorsiflexion, PL activity, and muscle co-activation. CONCLUSION: Our error-driven approach is feasible to reduce ankle inversion around heel contact in walking, and may have clinical implication on intervention of recurrent ankle sprains.

Neuromuscular control during stepping down in continuous gait in individuals with and without ankle instability.

Ankle sprains are a common injury and those affected are at a risk of developing chronic ankle instability (CAI). Complications of an acute sprain include increased risk of re-injury and persistent disability; however, the exact link between ankle sprains and chronic instability has yet to be elucidated. The purpose of this study was to investigate neuromuscular control (including kinematics, kinetics and EMG) during stepping down from a curb, a common yet challenging daily activity, in persons with ankle instability (n = 11), those with a history of ankle sprain without persistent instability, called ankle sprain "copers" (CPRs) (n = 9) and uninjured controls (CTLs) (n = 13). A significant group difference was noted as the CPR group demonstrated increased tibialis anterior activity in both the preparatory (pre-touchdown) and reactive (post-touchdown) phases when compared to healthy and unstable groups (P < 0.05). It follows that the CPR group also demonstrated a significantly less plantar-flexed position at touchdown than the other two groups (P < 0.05). This is a more stable position to load the ankle and this strategy differed from that used by participants with CAI and uninjured CTLs. These findings provide insight into the neuromuscular control strategies of CPRs, which may allow them to more appropriately control ankle stability following sprains.

The relationship between impact force, neck strength, and neurocognitive performance in soccer heading in adolescent females.

Head impacts are common in contact sports, but only recently has there been a rising awareness of the effects of subconcussive impacts in adolescent athletes. A better understanding of how to attenuate head impacts is needed and therefore, this study investigated the relationship between neck strength, impact, and neurocognitive function in an acute bout of soccer heading in a sample of female high school varsity soccer players. Seventeen participants completed the ImPACT neurocognitive test and had their isometric neck strength tested (flexion, extension, and bilateral flexion) before heading drills. Each participant was outfitted with custom headgear with timing switches and a three-dimensional accelerometer affixed to the back of the head, which allowed for measurement of impact during heading. Participants performed a series of 15 directional headers, including 5 forward, 5 left and 5 right headers in a random order, then completed the ImPACT test again. Neurocognitive tests revealed no significant changes following heading. However, there were statistically significant, moderate, negative correlations (r = -0.500:-0.757, p < .05) between neck strength and resultant header acceleration, indicating that those with weaker necks sustained greater impacts. This suggests neck strengthening may be an important component of any head injury prevention/reduction program.

EMG and tibial shock upon the first attempt at barefoot running.

As a potential means to decrease their risk of injury, many runners are transitioning into barefoot running. Habitually shod runners tend to heel-strike (SHS), landing on their heel first, while barefoot runners tend to mid-foot or toe-strike (BTS), landing flat-footed or on the ball of their foot before bringing down the rest of the foot including the heel. This study compared muscle activity, tibial shock, and knee flexion angle in subjects between shod and barefoot conditions. Eighteen habitually SHS recreational runners ran for 3 separate 7-minute trials, including SHS, barefoot heel-strike (BHS), and BTS conditions. EMG, tibial shock, and knee flexion angle were monitored using bipolar surface electrodes, an accelerometer, and an electrogoniometer, respectively. A one-way MANOVA for repeated measures was conducted and several significant changes were noted between SHS and BTS, including significant increases in average EMG of the medial gastrocnemius (p=.05), average and peak tibial shock (p<.01), and the minimum knee flexion angle (p<.01). Based on our data, the initial change in mechanics may have detrimental effects on the runner. While it has been argued that BTS running may ultimately be less injurious, these data indicate that habitually SHS runners who choose to transition into a BTS technique must undertake the process cautiously.

Coordination variability during load carriage walking: can it contribute to low back pain?

Load carriage walking is frequently associated with low back pain. Mechanical stress is a potential cause of such pain, and a lack of coordination variability may produce mechanical stress. We tested the hypothesis that coordination variability would decrease during load carriage walking. We examined the trunk-thigh coordination variability in the sagittal and frontal planes and the thorax-pelvis coordination variability in the transverse plane. Ten healthy participants were recruited to perform unloaded and load carriage walking. Coordination variability was quantified as the standard deviation of continuous relative phase between two segments across a number of walking trials. During load carriage walking, the coordination variability significantly increased rather than decreased in the sagittal and transverse planes, and it did not change significantly in the frontal plane compared to those during unloaded walking. The findings rejected the hypothesis and suggested that reduced coordination variability may not predict the development of low back pain associate with load carriage walking in healthy people.

Examining neuromuscular control during landings on a supinating platform in persons with and without ankle instability.

BACKGROUND: Ankle instability is a costly public health concern because of the associated recurrent sprains. It is evident there are neuromuscular control deficits predisposing these individuals to their ankle "giving way." Individuals with a history of lateral ankle sprain, who did not develop instability, may hold the key to understanding proper neuromuscular control after injury. HYPOTHESES: On the basis of previous research, the authors hypothesized that individuals with ankle instability would demonstrate reduced peroneal activation, causing a more inverted position of the ankle, before and after landing. STUDY DESIGN: Controlled laboratory study. METHODS: This study aimed to evaluate preparatory and reactive neuromuscular control when landing on a custom-designed ankle supinating device in individuals with ankle instability (AI), individuals with a history of lateral ankle sprains without instability (LAS), and uninjured controls (CON). Forty-five participants (15 per group) were asked to land on a device built to simulate the mechanism of a lateral ankle sprain (supination) while kinematics and muscle activity of the lower extremity were monitored. RESULTS: Contrary to our hypotheses, the AI group displayed significantly increased preparatory (P = .01) and reactive (P = .02) peroneal activation, while the LAS group demonstrated a trend toward increased preparatory tibialis anterior muscle activation (P = .07), leading to a decreased plantar flexion of the ankle at landing. CONCLUSION: The AI group was likely acting in a protective fashion to a potentially injurious situation, indicating these individuals can activate the peroneals if needed. The LAS group's strategy may be a safer strategy in that a less plantar-flexed position of the ankle is more close-packed and stable. Further, it appears the long-latency response of the peroneals may be enhanced in these individuals, which indicates motor learning at the supraspinal level to promote dynamic restraint. CLINICAL RELEVANCE: Individuals with AI can increase peroneal activation when necessary to dynamically stabilize the ankle, indicating the potential for training/rehabilitation. Further, the LAS group may deploy a different control strategy after injury to protect the ankle from subsequent sprains, which deserves investigation during activities of daily living. A greater understanding of these strategies will lead to the development of more appropriate treatment paradigms after injury to minimize the incidence of instability.

Temporal relationship between trunk and thigh contributes to balance control in load carriage walking.

Load carriage walking (LCW) challenges a person's balance as the load increases their forward trunk inclination, shifting the center of mass (COM) forward with respect to the base of support (BOS). We examined LCW to understand whether and how healthy people adjust the temporal relationship (TR) between the trunk and leg for balance control. Ten subjects were recruited to perform unloaded walking and LCW. The TR between the trunk and leg was measured by the continuous relative phase. The maximum forward displacement of the COM with respective to the BOS (FDCOM(BOS)) was recorded during the stance phase. We found that the TR was shifted in LCW, and the shift was associated with a decrease in the maximum FDCOM(BOS). The findings suggest that the TR between the trunk and leg contributes to balance control, and it may be a variable that needs to be addressed in gait rehabilitation.

Effect of knee joint cooling on the electromyographic activity of lower extremity muscles during a plyometric exercise.

During sporting events, injured athletes often return to competition after icing because of the reduction in pain. Although some controversy exists, several studies suggest that cryotherapy causes a decrease in muscle activity, which may lead to a higher risk of injury upon return to play. The purpose of this study was to investigate the effect of a 20-min knee joint cryotherapy application on the electromyographic activity of leg muscles during a single-leg drop jump in twenty healthy subjects, randomly assigned to an experimental and a control group. After the pre-tests, a crushed-ice bag was applied to the knee joint of the experimental group subjects for 20 min, while the control group subjects rested for 20 min. All subjects were retested immediately after this period and retested again after another 20 min of rest. Average electromyographic activity and ground contact time were calculated for the pre- and post-test sessions. Decreases in electromyographic activity of the lower extremity musculature were found in pre-activation, eccentric (braking), and concentric (push-off) phases immediately after the icing, and after 20 min of rest. The results lend support to the suggestion that cryotherapy during sporting events may place the individuals in a vulnerable position.

A novel dynamic ankle-supinating device.

Lateral ankle sprains (LAS) are among the most common joint injuries, and although most are resolved with conservative treatment, others develop chronic ankle instability (AI). Considerable attention has been directed toward understanding the underlying causes of this pathology; however, little is known concerning the neuromuscular mechanisms behind AI. A biomechanical analysis of the landing phase of a drop jump onto a device that simulates the mechanism of a LAS may give insight into the dynamic restraint mechanisms of the ankle by individuals with AI. Furthermore, work evaluating subjects who have a history of at least one lateral ankle sprain, yet did not develop AI, may help elucidate compensatory mechanisms following a LAS event. Identifying proper neuromuscular control strategies is crucial in reducing the incidence of AI.

Neuromuscular control and ankle instability.

Lateral ankle sprains (LAS) are common injuries in athletics and daily activity. Although most are resolved with conservative treatment, others develop chronic ankle instability (AI)-a condition associated with persistent pain, weakness, and instability-both mechanical (such as ligamentous laxity) and functional (neuromuscular impairment with or without mechanical laxity). The predominant theory in AI is one of articular deafferentation from the injury, affecting closed-loop (feedback/reflexive) neuromuscular control, but recent research has called that theory into question. A considerable amount of attention has been directed toward understanding the underlying causes of this pathology; however, little is known concerning the neuromuscular mechanisms behind the development of AI. The purpose of this review is to summarize the available literature on neuromuscular control in uninjured individuals and individuals with AI. Based on available research and reasonable speculation, it seems that open-loop (feedforward/anticipatory) neuromuscular control may be more important for the maintenance of dynamic joint stability than closed-loop control systems that rely primarily on proprioception. Therefore, incorporating perturbation activities into patient rehabilitation schemes may be of some benefit in enhancing these open-loop control mechanisms. Despite the amount of research conducted in this area, analysis of individuals with AI during dynamic conditions is limited. Future work should aim to evaluate dynamic perturbations in individuals with AI, as well as subjects who have a history of at least one LAS and never experienced recurrent symptoms. These potential findings may help elucidate some compensatory mechanisms, or more appropriate neuromuscular control strategies after an LAS event, thus laying the groundwork for future intervention studies that can attempt to reduce the incidence and severity of acute and chronic lateral ankle injury.

A biomechanical comparison of back and front squats in healthy trained individuals.

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.

The effect of fatigue and habituation on the stretch reflex of the ankle musculature.

Many ankle injuries are said to occur when athletes are in a fatigued state; therefore, studies investigating the role that fatigue plays in ankle injuries are warranted. Furthermore, the contributions of the stretch reflex in countering the injury mechanism are still unclear. We hypothesized that (1) fatigue would impair the reflex response, (2) there would be no differences between genders, (3) habituation would be present, and (4) fatigue would exacerbate the effect of habituation. Forty healthy subjects participated and were divided into treatment and control groups. Stretch reflex measurements were taken for the tibialis anterior (TA), peroneus longus (PL), and peroneus brevis (PB) muscles in response to a rapid inversion perturbation. A fatigue intervention was administered to the treatment group, while the control group sat quietly. Post-test measurements were recorded within 5min and reflex latency (RL) and amplitude (RA) were calculated. RA decreased significantly, however a significant improvement was noted in RL in the PL and PB muscles. The effect that peripheral fatigue has on RL should not be considered a cause of ankle injuries. However, the diminished RA may suggest reduced dynamic stability after fatigue. Habituation was present and was exacerbated by fatigue, indicating that reflex testing is affected by fatigue and habituation, which must be taken into consideration in future studies.

Purposeful heading during a season does not influence cognitive function or balance in female soccer players.

Soccer participation, especially among females, is growing in popularity in the United States. Purposeful heading, an important soccer skill, has recently been scrutinized for safety reasons. The purpose of this study was to determine whether there was a relationship between purposeful heading and scores on cognitive function and balance in high school and collegiate female soccer players. Prior to and following the soccer season, all players and members of the control group were given a battery of neuropsychological and balance tests. There were no significant correlations found between the total number of game headers and performance on either balance or neuropsychological testing.Differences were noted in adjusted balance scores postseason between the collegiate players and the other two groups.However, no differences were revealed in neurocognitive performance between the three groups.

Effect of fatigue on neuromuscular function at the ankle.

CONTEXT: Lateral ankle sprains occur more frequently than any other orthopedic injury. Athletes often report sustaining more injuries late in competition when fatigue is present. OBJECTIVE: To evaluate neuromuscular function of the ankle musculature after fatigue. DESIGN: Experimental, pretest-posttest. SETTING: Research laboratory. PARTICIPANTS: Ten female and 9 male college-aged subjects. INTERVENTION: Fatigue was induced via continuous concentric and eccentric muscle actions of the ankle: inversion (INV), eversion (EV), plantar flexion (PF), and dorsiflexion (DF). MAIN OUTCOME MEASURES: Peak torque (PT), peak EMG, and median frequency (MF) were calculated prefatigue and postfatigue in the tibialis anterior (TA), peroneus longus (PER), and lateral gastrocnemius (GAS) muscles. RESULTS: Main effects were noted for test (P < 0.0125) in all statistical tests performed indicating changes in PT, peak EMG, and MF after fatigue. CONCLUSIONS: A significant decrease in MF of the PER muscle after PF fatigue and corresponding with a decreased firing rate, may be of importance, especially with regard to the role in countering the violent moment seen with inversion ankle sprains.

Resistance training improves gait kinematics in persons with multiple sclerosis.

OBJECTIVE: To evaluate the effects of an 8-week lower-body resistance-training program on walking mechanics in persons with multiple sclerosis (MS). DESIGN: Repeated-measures design, evaluating gait kinematics before and after an 8-week progressive resistance-training intervention. SETTING: Biomechanics laboratory and fitness center (with conventional, commercially available resistance-training equipment). PARTICIPANTS: Eight ambulatory subjects with MS (age, 46.0+/-11.5 y) with Expanded Disability Status Scale scores ranging from 2.5 to 5.5. INTERVENTION: An 8-week progressive resistance-training program. MAIN OUTCOME MEASURES: Kinematic gait parameters including knee range of motion, duration of stance, swing, and double-support phases in seconds and as percentages of the stride time, percentage of stride time spent in stance, swing, and double-support phases, step length, foot angle, stride length, velocity, step width, and toe clearance for both the more affected and less affected lower limbs. Isometric strength, 3-minute stepping, fatigue, and self-reported disability were also measured. RESULTS: After 2 months of resistance training, there were significant increases (P<.05) in percentage of stride time in the swing phase, step length, stride length, and foot angle; and significant decreases (P<.05) in percentage of stride time in the stance and double-support phases, duration of the double-support phase, and toe clearance. Isometric leg strength improved (P<.05) in 2 of the 4 muscle groups tested. Fatigue indices decreased (P=.04), whereas self-reported disability tended to decrease (P=.07) following the training program. Three-minute stepping increased by 8.7%. CONCLUSIONS: Resistance training may be an effective intervention strategy for improving walking and functional ability in moderately disabled persons with MS.