The influence of occupational footwear on dynamic balance perturbations

When mechanical engineering inspired from physiology improves postural-related somatosensory processes

Despite numerous studies uncovering the neural signature of tactile processing, tactile afferent inputs relating to the contact surface has not been studied so far. Foot tactile receptors being the first stimulated by the relative movement of the foot skin and the underneath moving support play an important role in the sensorimotor transformation giving rise to a postural reaction. A biomimetic surface, i.e., complying with the skin dermatoglyphs and tactile receptors characteristics should facilitate the cortical processes. Participants (n = 15) stood either on a biomimetic surface or on two control surfaces, when a sudden acceleration of the supporting surface was triggered (experiment 1). A larger intensity and shorter somatosensory response (i.e., SEP) was evoked by the biomimetic surface motion. This result and the associated decrease of theta activity (5-7 Hz) over the posterior parietal cortex suggest that increasing the amount of sensory input processing could make the balance task less challenging when standing on a biomimetic surface. This key point was confirmed by a second experiment (n = 21) where a cognitive task was added, hence decreasing the attentional resources devoted to the balance motor task. Greater efficiency of the postural reaction was observed while standing on the biomimetic than on the control surfaces.

The biomechanical differences of wearing safety shoes compared with everyday shoes on dynamic balance when tripping over an obstacle

Safety shoes are known to challenge dynamic balance, but the interaction between footwear and trips has not been thoroughly explored. This study investigated the biomechanical differences on dynamic balance during unexpected trip perturbations between safety shoes and everyday shoes. The vertical position of the whole-body center of mass (CoM) and the linear momentum of the swing leg from seven females and sixteen males were analyzed in five subsequent gait cycles. Additionally, the recovery strategies (i.e., the displacement of the foot after tripping) were classified. Wearing safety shoes, the linear momentum of the foot and whole leg increased, and the vertical position of the whole-body CoM was lower after the perturbation. Additionally, the recovery strategy when wearing safety shoes demonstrated a lower displacement of the foot. In conclusion, wearing safety shoes was found to have negative biomechanical effects when having to circumvent a trip, and this potentially increased the risk of falling.

Sensory Organization Test Conditions Influence Postural Strategy Rather than Footwear or Workload

BACKGROUND

Postural strategies such as ankle, hip, or combined ankle-hip strategies are used to maintain optimal postural stability, which can be influenced by the footwear type and physiological workload.

PURPOSE

This paper reports previously unreported postural strategy scores during the six conditions of the sensory organization test (SOT).

METHODS

Fourteen healthy males (age: 23.6 ± 1.2 years; height: 181 ± 5.3 cm; mass: 89.2 ± 14.6 kg) were tested for postural strategy adopted during SOT in three types of occupational footwear (steel-toed work boot, tactical work boot, low-top work shoe) every 30 min during a 4-h simulated occupational workload. Postural strategy scores were analyzed using repeated measures analysis of variance at 0.05 alpha level.

RESULTS

Significant differences among postural strategy scores were only evident between SOT conditions, and but not between footwear type or the workload.

CONCLUSIONS

Findings indicate that occupational footwear and occupational workload did not cause a significant change in reliance on postural strategies. The significant changes in postural strategy scores were due to the availability of accurate and/or conflicting sensory feedback during SOT conditions. In SOT conditions where all three types of sensory feedback was available, the ankle strategy was predominantly adopted, while more reliance on hip strategy occurred in conditions with absent or conflicting sensory feedback.

Shorter work boot shaft height improves ankle range of motion and decreases the oxygen cost of work

Work boots featuring design elements implemented to protect the foot and lower limb are common in many industries. However, boot design can have negative unintended consequences such as increases in work related fatigue and injury risk. This study compared joint kinematics and the physiological cost of two commercially available steel-toed work boots with different shaft designs worn throughout a simulated work task. A boot with a lower-cut and scalloped shaft allowed greater sagittal plane range of motion at the ankle joint compared to a boot with a higher-cut straight shaft, particularly in the late stance phase of the gait cycle. This was coupled with a decreased physiological cost of treadmill walking (2.6 and 3.1% improvement in oxygen consumption and walking economy, respectively), likely caused by a more efficient gait pattern. A lower-cut and scalloped shaft could lead to decreases in work-related fatigue and the subsequent risk of injuries in workers. Practitioner summary: Gait kinematics and the physiological cost of work boots with different shaft heights has not previously been investigated. A randomised cross-over study design found that a boot with a lower shaft height and scalloped collar improved ankle range of motion and reduced the physiological cost experienced by the wearers. Abbreviations: ROM: range of motion; FS: full shaft; SS: scalloped shaft; COM: centre of mass; HR: heart rate; RPE: rating of perceived exertion; ES: effect size.

Impact of Prolonged Exposure to a Slippery Surface on Postural Stability

Falls are extremely common in occupational settings. Intrinsic factors such as overexertion and extrinsic factors such as the supporting surface are causative factors of falls. The impact of prolonged exposure to a slippery surface on postural stability has not been previously studied. The purpose of the study was to analyze the effect of extended exposure to a dry and a slippery surface on postural stability. Eighteen males (age: 21.17 ± 3.38 years; height: 1.77 ± 0.08 m; mass: 89.81 ± 14.23 kg) were recruited and subjected to one-hour walking on a dry surface and a slippery surface on two different days. Participants’ balance was assessed using a force platform in stable and unstable conditions at 0, 30, and 60 min. Postural sway variables were analyzed using a 2 (surface) × 3 (time) repeated-measures ANOVA. Significant time main effects were observed in the stable condition with greater balance decrements at 30 and 60 min. Greater balance decrements were observed on the slippery surface compared to the dry surface in the unstable condition. The balance decrements can be attributed to overexertion due to the physiological workload of prolonged walking and to the potential gait modifications due to walking on the slippery surface.

Lower Extremity Muscle Activation in Alternative Footwear during Stance Phase of Slip Events

Muscle activity from the slipping leg have been previously used to analyze slip induced falls. However, the impact of casual alternative footwear on slipping leg muscle activity when exposed to slippery environments is still unknown. The purpose of the study was to analyze the impact of alternative footwear (crocs (CC) and flip-flops (FF)) compared to slip-resistant footwear (LT) on lower extremity muscle activity when exposed to dry gait (NG), unexpected (US), alert (AS), and expected slips (ES). Eighteen healthy males (age: 22.3 ± 2.2 years; height: 177.7 ± 6.9 cm; weight: 79.3 ± 7.6 kg) completed the study in a repeated measures design in three footwear sessions separated by 48 h. Electromyography (EMG) muscle activity from four muscles of the lead/slipping leg was measured during the stance phase of the gait-slip trials. A 3 (footwear) × 4 (gait-slip trials) repeated measures analysis of variance was used to analyze EMG dependent variables mean, peak, and percent of maximal voluntary contraction. Greater lower extremity muscle activation during the stance phase was seen in US and AS conditions compared to NG and ES. In addition, footwear differences were seen for the alternative footwear (CC and FF) during US and AS, while the low top slip resistant shoe had no differences across all gait trials, suggesting it as the most efficient footwear of choice, especially when maneuvering slippery flooring conditions, either with or without the knowledge of an impending slip.

Muscle Activity during Postural Stability Tasks: Role of Military Footwear and Load Carriage

Decrements to postural control manifest as an increase in muscle activity, indicating continuous attempts to maintain body equilibrium and postural stability. Extrinsic factors such as footwear, and intrinsic factors such as muscle fatigue, can affect postural stability. The purpose of this study was to analyze the impact of two types of military footwear and a military-type load-carrying task on lower extremity muscle activity during various postural stability tasks. Sixteen males’ (age: 26.63 ± 3.93 years; mass: 87 ± 12.4 kg; height: 178.04 ± 6.2 cm) muscle activity from knee flexors, extensors, ankle dorsiflexors, and plantar flexors were measured using electromyography in standard (STD) and minimalist (MIN) military footwear, before (PRE) and after (POST) a simulated workload during sensory organization and motor control tests on the Neurocom EquitestTM. Mean muscle activity was analyzed using 2 (footwear) × 2 (time) repeated measures ANOVA with an alpha level of 0.05. Results revealed a requirement of significantly greater muscle activity in POST and STD. MIN demonstrated lesser balance decrements POST workload, which could be attributed to its design characteristics. Results will help in suggesting footwear design characteristics to minimize muscular exertion while eliciting better postural control, and to prevent postural instability due to overexertion in military personnel.

Does Minimalist Footwear Design Aid in Postural Stability and Fall Prevention in Ergonomics?

The purpose of the article is to identify if novel footwear design could aid in postural stability and fall prevention in workplace. Footwear design has been reported to aid the task of maintaining postural stability or balancing in an erect stance while minimizing risk of falls. Minimalistic footwear that has design features such as low mass, lower heel height, and thin midsole can positively influence postural stability. Minimalistic military footwear has been shown to lower incidences of falls with efficient muscular effort. Occupational footwear that abides by safety standards with minimalistic features can help maintain postural stability and reduce falls.

The Interaction of Cognitive Interference, Standing Surface, and Fatigue on Lower Extremity Muscle Activity

Background

Performing cognitive tasks and muscular fatigue have been shown to increase muscle activity of the lower extremity during quiet standing. A common intervention to reduce muscular fatigue is to provide a softer shoe-surface interface. However, little is known regarding how muscle activity is affected by softer shoe-surface interfaces during static standing. The purpose of this study was to assess lower extremity muscular activity during erect standing on three different standing surfaces, before and after an acute workload and during cognitive tasks.

Methods

Surface electromyography was collected on ankle dorsiflexors and plantarflexors, and knee flexors and extensors of fifteen male participants. Dependent electromyography variables of mean, peak, root mean square, and cocontraction index were calculated and analyzed with a 2 × 2 × 3 within-subject repeated measures analysis of variance.

Results

Pre-workload muscle activity did not differ between surfaces and cognitive task conditions. However, greater muscle activity during post-workload balance assessment was found, specifically during the cognitive task. Cognitive task errors did not differ between surface and workload.

Conclusions

The cognitive task after workload increased lower extremity muscular activity compared to quite standing, irrespective of the surface condition, suggesting an increased demand was placed on the postural control system as the result of both fatigue and cognitive task.

Impact of military type footwear and load carrying workload on postural stability

Postural stability has been shown to be impacted by footwear and task performed. This study analysed the impact of two military footwear, standard boot (STB) and minimalist boot (MTB) on postural stability, before (PRE) and after (POST) a load carriage task. Sixteen participants were tested for postural stability using sensory organisation and motor control tests on Neurocom Equitest™. Postural sway, equilibrium scores and postural latencies were analysed using a two-factor repeated measures ANOVA: boot type (STB-MTB) × time (PRE-POST) load carriage task. Significantly greater postural sway variables, lower balance scores and slower postural latencies were seen in STB and POST load carriage conditions (p < .05). The results suggest that MTB exhibited greater balance compared to STB in balance conditions that rely on somatosensory feedback and that balance is lowered after a load carriage task. Decrements in postural stability could be attributed to boot design characteristics and muscular exertion due to the load carriage task. Practitioner Summary: Maintaining optimal postural stability is crucial in military. Impact of military footwear types and load carriage task on postural stability are addressed. Findings provide footwear design and physical exertion implications on postural stability leading to potential interventions that reduce postural stability decrements; thereby, reducing potential falls and fall related injuries.

The Effects of Exercise Induced Muscle Damage on Knee Joint Torque and Balance Performance

The purpose of this investigation is to determine the effects of exercise induced muscle damage (EIMD) on balance and knee joint torque. Thirteen males and females volunteered to participate in the study. Following a familiarization session, baseline measures were obtained for isometric torque measured during a maximal voluntary isometric contraction (MVIC) for knee flexors and extensors, and ankle dorsi-flexors and plantar-flexors. Additionally, balance performance was tested in double leg (DL), and right single leg (RSL) static and dynamic unstable stability was measured. Participants then performed the muscle damage protocol of front loaded Bulgarian split squats. All measurements were re-assessed for torque and balance immediately and up to 72 h afterwards. A one-way repeated-measures analysis of variance (ANOVA) was used to analyze differences between baseline and all time-points for torque and balance measures. There was a significant time effect for knee extensors MVIC torque, where baseline measures are greater than post EIMD, 24 h and 48 h post EIMD. There was no significant time effect for all balance conditions. These results provide evidence of EIMD following high intensity eccentric exercises with significant reductions in knee extensor torque up to at least 48 h and show that balance was not compromised following EIMD.

Motor adaption during repeated motor control testing: Attenuated muscle activation without changes in response latencies

With repeated exposure to postural perturbations the human postural control system can adapt and create efficient strategies to counteract these perturbations. The Motor Control Test (MCT) is commonly used to elicit reactionary postural movements. Though this device has been assessed for possible learning effects and reliability of composite scores, yet no study has evaluated possible neuromuscular alterations repeated bouts might elicit. Twenty participants (age: 25 ± 4.73 years; height: 183.8 ± 8.5 cm; mass: 85.2 ± 15.6 kg) volunteered and, following familiarization, performed five full-randomized MCTs over six testing sessions. The first five sessions occurred on consecutive days, with the sixth occurring two days later. Electromyography (EMG) was recorded on right lower extremity knee flexors and extensors, and ankle plantarflexors and dorsiflexors. Response latencies and Mean and RMS muscle activity were calculated and analyzed using 1 × 5 (within days) and 1 × 6 (across days) RM ANOVA. Decreases in muscle activation of proximal musculature were noted between days and trials within days, however these changes were not maintained after the two-day retention period. No differences were detected for MCT scores. These results suggest repeated MCT exposure modifies neuromuscular responses to maintain similar reaction time through a postural control strategy shift.

The role of military footwear and workload on ground reaction forces during a simulated lateral ankle sprain mechanism

BACKGROUND

Ankle sprains are a common orthopedic injury in military populations, which may be attributed to occupational demands and footwear. Minimalist military boots have become popular, but their influence on ground reaction force (GRF) attenuation capabilities during an ankle inversion perturbation are unknown. Therefore, the purpose of this study was to examine potential differences in GRFs during an ankle inversion perturbation in a standard issue (STN) and minimalist military boot (MIN) before and after a simulated military workload.

METHODS

Twenty-one healthy adult males completed an ankle inversion perturbation protocol in each footwear condition before and after an incremental treadmill exercise protocol to volitional exhaustion while wearing a 16kg rucksack. The ankle inversion perturbation protocol consisted of stepping down from a 27cm box onto a force platform with a fulcrum (FUL), which created 25° of inversion upon landing, or flat (FLT) outer sole attached to the plantar aspect of the participants' footwear in random order. Peak vertical, anterior/posterior, and medial/lateral components of the GRF during FUL and FLT conditions were assessed, normalized to multiples of body weight in each footwear. Dependent variables were then analyzed using separate 2 (footwear)×2 (time) repeated measures ANOVA (p<0.05).

RESULTS

The MIN footwear demonstrated significantly greater vertical GRF and significantly less medial GRF during the FUL condition.

CONCLUSIONS

These results indicate that various mechanical and design characteristics of military footwear may influence GRF attenuation capabilities and ankle joint loading when the foot/ankle complex is forced into inversion.

The Influence of an Acute Bout of Whole Body Vibration on Human Postural Control Responses

The use of vibrating platforms has become increasingly available, and popular at sports and rehabilitation institutes. Given the discrepancies in the literature regarding whole body vibration (WBV) and human reflexive responses, the purpose of this study was to examine the acute effects of WBV on postural response latencies, as well as associated electromyography measures of the lower extremities during balance perturbations. Reflexive responses during backward and forward balance perturbations were examined before, after, and 10 min after a bout of WBV. The findings suggest that following an acute bout of whole body vibration, muscle activity of the lower extremities is decreased during a reflexive response to an unexpected perturbation, and may be associated with faster reaction time.

Slip initiation in alternative and slip-resistant footwear

Slips occur as a result of failure of normal locomotion. The purpose of this study is to analyze the impact of alternative footwear (Crocs™, flip-flops) and an industry standard low-top slip-resistant shoe (SRS) under multiple gait trials (normal dry, unexpected slip, alert slip and expected slip) on lower extremity joint kinematics, kinetics and muscle activity. Eighteen healthy male participants (age: 22.28 ± 2.2 years; height: 177.66 ± 6.9 cm; mass: 79.27 ± 7.6 kg) completed the study. Kinematic, kinetic and muscle activity variables were analyzed using a 3(footwear) × 4(gait trials) repeated-measures analysis of variance at p = 0.05. Greater plantar flexion angles, lower ground reaction forces and greater muscle activity were seen on slip trials with the alternative footwear. During slip events, SRS closely resembled normal dry biomechanics, suggesting it to be a safer footwear choice compared with alternative footwear.