Effect of sloped walking on lower limb muscle forces

Concentric and eccentric hip musculotendon work depends on backpack loads and walking slopes

Hip muscle weakness is associated with low back and leg injuries. In addition, hiking with heavy loads is linked to high incidence of overuse injuries. Walking with heavy loads on slopes alters hip biomechanics compared to unloaded walking, but individual muscle mechanical work in these challenging conditions is unknown. Using movement simulations, we quantified hip muscle concentric and eccentric work during walking on 0° and ±10° slopes with, and without 40% bodyweight added loads, and with and without a hip belt. For gluteus maximus, psoas, iliacus, gluteus medius, and biceps femoris long head, both concentric and eccentric work were greatest during uphill walking. For rectus femoris and semimembranosus, concentric work was greatest during uphill and eccentric work was greatest during downhill walking. Loaded walking had greater concentric and eccentric work from rectus femoris, biceps femoris long head, and gluteus maximus. Psoas concentric work was greatest while carrying loads regardless of hip belt usage, but eccentric work was only greater than unloaded walking when using a hip belt. Loaded and uphill walking had high concentric work from gluteus maximus, and high eccentric work from gluteus medius and biceps femoris long head. Carrying heavy loads uphill may lead to excessive hip muscle fatigue and heightened injury risk. Effects of the greater eccentric work from hip flexors when wearing a hip belt on lumbar spine forces and pelvic stability should be investigated. Military and other occupational groups who carry heavy backpacks with hip belts should maintain eccentric strength of hip flexors and hamstrings.

A forefoot strike pattern during 18° uphill walking leads to greater ankle joint and plantar flexor loading

BACKGROUND

The ankle joint is one of the most involved joints in uphill walking. Furthermore, it is well known that toe walking increases the external dorsiflexion moment in the first half of stance during level walking. However, the effects of different foot-strike patterns on plantar flexor muscle forces, ankle joint forces, and other lower limb joint and muscle forces are unknown.

RESEARCH QUESTION

Do foot-strike patterns during 18° uphill walking affect lower limb sagittal joint angles and moments, as well as joint contact and muscle forces?

METHODS

This study was based on a data subset from previous publications, analysing uphill walking on an 18° ramp at a preset speed of 1.1 m/s in 18 male participants (34 limbs analyzed, 27 ± 5 years). Participants were divided into two groups based on their foot-strike pattern at initial contact: heel (HC) and forefoot (FC). Lower limb sagittal joint angles and moments as well as joint contact and muscle forces were assessed. Differences between the groups were assessed using two-sample t-tests.

RESULTS

FC showed increased soleus and gastrocnemius muscle forces as well as ankle joint forces during loading response and mid stance compared to HC. The soleus muscle force impulse was 51.1% higher in the FC group than in the HC group (p < 0.001). On the other hand, FC had a lower absolute centre of mass vertical displacement and reduced knee and hip joint, as well as iliopsoas and hamstring muscle force impulses.

SIGNIFICANCE

In terms of plantar flexor and ankle joint loading, it is advantageous to exhibit a heel strike pattern. The current results can be used to recommend foot-strike patterns for uphill walking, particularly in the presence or prevention of musculoskeletal issues.

Detection of intermuscular coordination based on the causality of empirical mode decomposition

Considering the stochastic nature of electromyographic (EMG) signals, nonlinear methods may be a more accurate approach to study intermuscular coordination than the linear approach. The aims of this study were to assess the coordination between two ankle plantar flexors using EMG by applying the causal decomposition approach and assessing whether the intermuscular coordination is affected by the slope of the treadmill. The medial gastrocnemius (MG) and soleus muscles (SOL) were analyzed during the treadmill walking at inclinations of 0°, 5°, and 10°. The coordination was evaluated using ensemble empirical mode decomposition, and the causal interaction was encoded by the instantaneous phase dependence of time series bi-directional causality. To estimate the mutual predictability between MG and SOL, the cross-approximate entropy (XApEn) was assessed. The maximal causal interaction was observed between 40 and 75 Hz independent of inclination. XApEn showed a significant decrease between 0° and 5° (p = 0.028), between 5° and 10° (p = 0.038), and between 0° and 10° (p = 0.014), indicating an increase in coordination. Thus, causal decomposition is an appropriate methodology to study intermuscular coordination. These results indicate that the variation of loading through the change in treadmill inclination increases the interaction of the shared input between MG and SOL, suggesting increased intermuscular coordination.

The effects of surface inclination on gastrocnemius, soleus and tibialis anterior muscle activation during gait

BACKGROUND

Inclined walking is associated with multiple musculoskeletal benefits and is considered a therapeutic exercise. Various patterns of increased and decreased muscle activation with inclined surfaces have been observed in normal muscles, with more focus on the proximal lower limb musculature.

OBJECTIVE

The aim of this study was to assess the differences in electromyographic activation of gastrocnemius, soleus, and tibialis anterior at various inclined surfaces during gait.

METHODS

Fourteen healthy male participants aged between 17-30 years walked at a self-selected speed at motor driven treadmill on 0, 2 and 4 degrees of inclination. EMG activity of the muscles was recorded using the Delsys Trigno surface EMG system.

RESULTS

Results showed that muscular activation of tibialis anterior significantly decreased with increase in the level of inclination (p< 0.05). However, soleus, gastrocnemius medialis and gastrocnemius lateralis showed no significant differences (p> 0.05) in their muscular activation, and no noticeable trends were found. Furthermore, no significant difference was found between all the muscles at ground level and inclined level 2 and 4.

CONCLUSION

These differences in activation patterns found in distal extremity can be useful for designing rehabilitation protocols in sports training and for patients with neurological and musculoskeletal pathologies.

The 6DOF knee kinematics of healthy subjects during sloped walking compared to level walking

BACKGROUND

Level Walking is a frequent functional movement during daily life. However, sloped walking is also common. Exploring 6DOF knee kinematics during sloped walking is important. It provides a reference for the rehabilitation, safety, and knee health of patients with knee diseases walking on sloped surfaces.

RESEARCH QUESTION

The study aimed to explore 6DOF knee kinematics characteristics during sloped walking compared to level walking. We hypothesized that tibial anteroposterior translation and flexion angle (the sagittal plane) were significantly different from those of level walking.

METHODS

One hundred young, healthy adults (50 males and 50 females) were recruited for this study. A three-dimensional gait analysis system was used to collect 6DOF knee kinematics during level and sloped walking. The slope was set to ± 15% when the sloped walking was performed.

RESULTS

Sloped walking mainly increased knee flexion angle (upslope, 2.5-26.2°, 1-100% gait cycle (GC), p < 0.05; downslope, 1.7-11.9°, 15-95% GC, p < 0.05) and anterior tibial translation (upslope, 0.7-4.1 mm, 3-54% GC & 0.6-2.1 mm, 80-94% GC; downslope, 1.0-2.2 mm, 21-69% GC) in the participants' knees. However, participants' other 4DOF knee kinematics during sloped walking were significantly different from those during level walking (p < 0.05). Participants had 'drastically changeable' knee kinematic alterations in the transverse and coronal plane (the other 4DOF knee kinematics) during sloped walking compared to level walking.

SIGNIFICANCE

Our results confirmed the hypothesis. Sloped walking significantly increased anterior tibial translation (in most GC) and flexion angle. These kinematic changes in healthy subjects should be evaluated and further explored for patients with knee diseases, such as anterior cruciate ligament deficiency. Our findings are meaningful for their rehabilitation or safety or knee health while walking on sloped surfaces. Our study may provide a pilot reference for the 6DOF knee kinematic exploration of sloped walking.

Effect of Assistance Using a Bilateral Robotic Knee Exoskeleton on Tibiofemoral Force Using a Neuromuscular Model

Tibiofemoral compression forces present during locomotion can result in high stress and risk damage to the knee. Powered assistance using a knee exoskeleton may reduce the knee load by reducing the work required by the muscles. However, the exact effect of assistance on the tibiofemoral force is unknown. The goal of this study was to investigate the effect of knee extension assistance during the early stance phase on the tibiofemoral force. Nine able-bodied adults walked on an inclined treadmill with a bilateral knee exoskeleton with assistance and with no assistance. Using an EMG-informed neuromusculoskeletal model, muscle forces were estimated, then utilized to estimate the tibiofemoral contact force. Results showed a 28% reduction in the knee moment, which resulted in approximately a 15% decrease in knee extensor muscle activation and a 20% reduction in subsequent muscle force, leading to a significant 10% reduction in peak and 9% reduction in average tibiofemoral contact force during the early stance phase (p < 0.05). The results indicate the tibiofemoral force is highly dependent on the knee kinetics and quadricep muscle activation due to their influence on knee extensor muscle forces, the primary contributor to the knee load.

Muscle forces and power are significantly reduced during walking in patients with peripheral artery disease

Patients with peripheral artery disease (PAD) have significantly reduced lower extremity muscle strength compared with healthy individuals as measured during isolated, single plane joint motion by isometric and isokinetic strength dynamometers. Alterations to the force contribution of muscles during walking caused by PAD are not well understood. Therefore, this study used simulations with PAD biomechanics data to understand lower extremity muscle functions in patients with PAD during walking and to compare that with healthy older individuals. A total of 12 patients with PAD and 10 age-matched healthy older controls walked across a 10-meter pathway with reflective markers on their lower limbs. Marker coordinates and ground reaction forces were recorded and exported to OpenSim software to perform gait simulations. Walking velocity, joint angles, muscle force, muscle power, and metabolic rate were calculated and compared between patients with PAD and healthy older controls. Our results suggest that patients with PAD walked slower with less hip extension during propulsion. Significant force and power reductions were observed in knee extensors during weight acceptance and in plantar flexors and hip flexors during propulsion in patients with PAD. The estimated metabolic rate of walking during stance was not different between patients with PAD and controls. This study is the first to analyze lower limb muscular responses during walking in patients with PAD using the OpenSim simulation software. The simulation results of this study identified important information about alterations to muscle force and power during walking in those with PAD.

Gait on slopes: Differences in temporo-spatial, kinematic and kinetic gait parameters between walking on a ramp and on a treadmill

BACKGROUND

Inclined treadmills or static ramp constructions can be used to investigate downhill gait in a standardised laboratory condition. There is a lack of information how the gait patterns are affected when walking on a ramp or an inclined treadmill during uphill and downhill walking.

RESEARCH QUESTION

Is there a difference in temporo-spatial parameters, sagittal ankle, knee and hip joint angle as well as ground reaction force when walking uphill and downhill on a ramp and a treadmill.

METHODS

Uphill and downhill gait of 15 healthy participants was assessed during walking on a treadmill and on a ramp with slope gradients of 12 °, 6 ° and 0 °. Participants were instructed to walk with the same speed on each slope-system. Kinematic and temporo-spatial paramters were collected using a 3D motion capture system (Qualisys, Gothenburgh, Sweden), kinetic data were collected using pressure insoles (loadsol®, Novel, Germany). Temporo-spatial parameters were analysed using a Friedman ANOVA, time series of kinematic and kinetic data were compared using statistical parametric mapping with a sigificance level of 5%.

RESULTS

On the treadmill participants walked with significantly shorter steps and shorter contact times, while they significantly increased step frequency compared to walking on a ramp, regardless of slope gradient. In uphill conditions, treadmill gait increased hip and knee flexion angles during the stance phase and increased the forward tilt of the thorax during the entire gait cycle. During downhill walking a significant decrease in dorsiflexion during initial contact, midstance and the second half of the swing phase was observed. Peak resultant forces remained similar compared to walking on the ramp. These alterations might be due to mechanical and psychological effects.

SIGNIFICANCE

Knowledge about these differences is important in future study design and data interpretation from existing literature.

Are Medial and Lateral Tibiofemoral Compressive Forces Different in Uphill Compared to Level Walking for Patients Following Total Knee Arthroplasty?

The purpose of this study was to determine how tibiofemoral joint compressive forces and knee joint-spanning muscle forces during uphill walking change compared to level walking in patients with total knee arthroplasty (TKA). A musculoskeletal model capable of resolving total (TCF), medial (MCF), and lateral (LCF) tibiofemoral compressive forces was used to determine compressive forces and muscle forces during level and uphill walking on a 10 deg incline for twenty-five post-TKA patients. A 2 × 2 (slope: level and 10 deg × limb: replaced and nonreplaced) repeated measures analysis of variance was used to detect differences in knee contact forces between slope and limb conditions and their interaction. Peak loading-response TCF, MCF, and LCF were greater during uphill walking than level walking for nonreplaced limbs. During uphill walking, peak loading-response TCF was smaller in replaced limbs compared to nonreplaced limbs with no change in MCF or LCF. Peak knee extension moment and knee extensor muscle force were smaller in replaced limbs compared to nonreplaced limbs during uphill walking. During level walking, replaced and nonreplaced limbs experienced rather equal joint loading; however, replaced limb experienced reduced joint loading during uphill walking. Differences in joint loading between replaced and nonreplaced limbs were not present during level walking, suggesting compensation from the replaced limb during the more difficult task. Uphill walking following TKA promotes more balanced loading of replaced limbs during stance; however, these benefits may come at the expense of increased loading on nonreplaced limbs.

Classification of Walking Environments Using Deep Learning Approach Based on Surface EMG Sensors Only

Classification of terrain is a vital component in giving suitable control to a walking assistive device for the various walking conditions. Although surface electromyography (sEMG) signals have been combined with inputs from other sensors to detect walking intention, no study has yet classified walking environments using sEMG only. Therefore, the purpose of this study is to classify the current walking environment based on the entire sEMG profile gathered from selected muscles in the lower extremities. The muscle activations of selected muscles in the lower extremities were measured in 27 participants while they walked over flat-ground, upstairs, downstairs, uphill, and downhill. An artificial neural network (ANN) was employed to classify these walking environments using the entire sEMG profile recorded for all muscles during the stance phase. The result shows that the ANN was able to classify the current walking environment with high accuracy of 96.3% when using activation from all muscles. When muscle activation from flexor/extensor groups in the knee, ankle, and metatarsophalangeal joints were used individually to classify the environment, the triceps surae muscle activation showed the highest classification accuracy of 88.9%. In conclusion, a current walking environment was classified with high accuracy using an ANN based on only sEMG signals.

Analysis of sloped gait: How many steps are needed to reach steady-state walking speed after gait initiation?

BACKGROUND

Gait initiation in level walking is suggested to take three steps before reaching steady-state walking speed. In sloped gait, it is not clear if the general recommendation of level gait can be used.

RESEARCH QUESTION

The aim of this study was to investigate (1) if steady-state walking speed is reached within four steps in sloped gait, and (2) to what extent the number of initial steps cause differences in step length, cadence and ground reaction force (GRF).

METHODS

Fourteen healthy participants walked on an instrumented ramp at inclinations of 0°, ±6°, ±12°, and ±18°, covering slight (clinical application) to steep (hiking and mountaineering) slopes. The starting position on the ramp was adjusted to collect each of the first to fourth step using a 12 infrared-camera motion capture system and two force plates. For each slope condition steady-state walking speed was determined using the ratio of the braking and propulsion impulse (ratio p_ap;p_brakingp_propulsion) and the resultant Centre of Mass (CoM) speed (vel_CoM). Statistical differences between steps were calculated by using a Friedman ANOVA and pairwise post-hoc Wilcoxon tests.

RESULTS

In all inclinations, ≥90 % (uphill) and ≥95 % (downhill) of steady-state speed regarding ratio p_ap and maximum vel_CoM was reached with the 3rd step. In the level and uphill condition the 4th step showed a slight decrease in vel_CoM. In uphill and downhill condition, the acceleration was mainly generated due to the increase in cadence with significant increases between the 1st and 2nd step as well as between the 2nd and 3rd step. A significant increase in step length was only observed in the uphill conditions.

SIGNIFICANCE

Steady-state walking speed was reached with the 3rd step and thus, walkways which allow for two initial steps seem to be appropriate for uphill and downhill gait analysis for inclinations up to ±18°.

Muscle Eccentric Contractions Increase in Downhill and High-Grade Uphill Walking

In Duchenne muscular dystrophy (DMD), one of the most severe and frequent genetic diseases in humans, dystrophic muscles are prone to damage caused by mechanical stresses during eccentric contractions. Eccentric contraction during walking on level ground likely contributes to the progression of degeneration in lower limb muscles. However, little is known about how the amount of muscle eccentric contractions is affected by uphill/downhill sloped walking, which is often encountered in patients’ daily lives and poses different biomechanical demands than level walking. By recreating the dynamic musculoskeletal simulations of downhill (−9°, −6°, and −3°), uphill (+3°, +6°, and +9°) and level walking (0°) from a published study of healthy participants, negative muscle mechanical work, as a measure of eccentric contraction, of 35 lower limb muscles was quantified and compared. Our results indicated that downhill walking overall induced more (32% at −9°, 19% at −6°, and 13% at −3°) eccentric contractions in lower limb muscles compared to level walking. In contrast, uphill walking led to eccentric contractions similar to level walking at low grades (+3° and +6°), but 17% more eccentric contraction at high grades (+9°). The changes of muscle eccentric contraction were largely predicted by the changes in both joint negative work and muscle coactivation in sloped walking. As muscle eccentric contractions play a critical role in the disease progression in DMD, this study provides an important baseline for future studies to safely improve rehabilitation strategies and exercise management for patients with DMD and other similar conditions.

Uphill walking at iso-efficiency speeds

Uphill walking gait has been extensively studied, but the optimal uphill speed able to enhance the metabolic demand without increasing fatigability has so far received little attention. Therefore, the aim of this study was to assess the metabolic/kinematic demand at constant speed (6 km·h^-1 G0 level, G2 2% uphill, G7 7% uphill) and at iso-efficiency speeds (G2IES 5.2 km·h^-1 2% uphill and G7IES 3.9 km·h^-1 7% uphill). For this aim, physically active women (n:24, Age 33.40 ± 4.97 years, BMI 21.62 ± 2.06 kg/m^-2) after an 8-min warm-up were studied on a treadmill for 10' for every walking condition with a 5' rest in between. Average heart rate (AVG-HR), rating of perceived exertion (RPE) and kinematic variables (stance time, swing time, stride length, stride cycle, stride-length variability, stride-cycle variability and internal work) were studied. Modifications in stance time, stride length and stride cycle (p<0.005), and lower internal-work values (p<0.001) occurred in G7IES in comparison to the other conditions. Swing time was significantly modified only in G7IES compared to G0 and G7 (p<0.001 and p<0.005, respectively). Stride-length variability and stride-cycle variability were higher in G7IES compared to the other conditions (p<0.001). G7 induced the highest AVG-HR (p<0.005) and RPE (p<0.001) compared to the other conditions. This study demonstrates that by applying the equation for uphill walking gait, it is possible to maintain a similar metabolic demand and RPE at iso-efficiency speeds during uphill compared to level walking, inducing at the same time a modification of the kinematic parameters of walking gait performed at the same slope condition.

EMG-Centered Multisensory Based Technologies for Pattern Recognition in Rehabilitation: State of the Art and Challenges

In the field of rehabilitation, the electromyography (EMG) signal plays an important role in interpreting patients' intentions and physical conditions. Nevertheless, utilizing merely the EMG signal suffers from difficulty in recognizing slight body movements, and the detection accuracy is strongly influenced by environmental factors. To address the above issues, multisensory integration-based EMG pattern recognition (PR) techniques have been developed in recent years, and fruitful results have been demonstrated in diverse rehabilitation scenarios, such as achieving high locomotion detection and prosthesis control accuracy. Owing to the importance and rapid development of the EMG centered multisensory fusion technologies in rehabilitation, this paper reviews both theories and applications in this emerging field. The principle of EMG signal generation and the current pattern recognition process are explained in detail, including signal preprocessing, feature extraction, classification algorithms, etc. Mechanisms of collaborations between two important multisensory fusion strategies (kinetic and kinematics) and EMG information are thoroughly explained; corresponding applications are studied, and the pros and cons are discussed. Finally, the main challenges in EMG centered multisensory pattern recognition are discussed, and a future research direction of this area is prospected.

Effects of Backpack Loads on Leg Muscle Activation during Slope Walking

Hikers and soldiers usually walk up and down slopes with a load carriage, causing injuries of the musculoskeletal system, especially during a prolonged load journey. The slope walking has been reported to lead to higher leg extensor muscle activities and joint moments. However, most of the studies investigated muscle activities or joint moments during slope walking without load carriage or only investigated the joint moment changes and muscle activities with load carriages during level walking. Whether the muscle activation such as the signal amplitude is influenced by the mixed factor of loads and grades and whether the influence of the degrees of loads and grades on different muscles are equal have not yet been investigated. To explore the effects of backpack loads on leg muscle activation during slope walking, ten young male participants walked at 1.11 m/s on a treadmill with different backpack loads (load masses: 0, 10, 20, and 30 kg) during slope walking (grade: 0, 3, 5, and 10°). Leg muscles, including the gluteus maximus (GM), rectus femoris (RF), hamstrings (HA), anterior tibialis (AT), and medial gastrocnemius (GA), were recorded during walking. The hip, knee, and ankle extensor muscle activations increased during the slope walking, and the hip muscles increased most among hip, knee, and ankle muscles (GM and HA increased by 46% to 207% and 110% to 226%, respectively, during walking steeper than 10° across all load masses (GM: p = 1.32 × 10−8 and HA: p = 2.33 × 10−16)). Muscle activation increased pronouncedly with loads, and the knee extensor muscles increased greater than the hip and ankle muscles (RF increased by 104% to 172% with a load mass greater than 30 kg across all grades (RF: p = 8.86 × 10−7)). The results in our study imply that the hip and knee muscles play an important role during slope walking with loads. The hip and knee extension movements during slope walking should be considerably assisted to lower the muscle activations, which will be useful for designing assistant devices, such as exoskeleton robots, to enhance hikers’ and soldiers’ walking abilities.

Does surface slope affect dual task performance and gait? An exploratory study in younger and older adults

An increased risk of falling is associated with changes in gait while dual-tasking. The degree to which gait stability is altered during walking is influenced by an individual's cognitive and postural capacity, and the difficulty of the presented tasks. However, it is unknown how greater walking task difficulty affects gait stability in younger and older adults when dual-tasking. The purpose of the current study was to determine the effect of walking task difficulty on gait stability in younger and older adults while performing a difficult audiospatial task. Ten younger [mean (SD) age 30.8 (6.6) years; 5 women] and 10 older [66.8 (5.7) years; 6 women] healthy adults walked on a treadmill at their preferred walking speed [younger 4.8 (0.4) ms^-1, older 4.5 (0.5) ms^-1) on either a level, or downhill slope both with and without responding to an audiospatial task. Step width, step width SD and mediolateral centre of mass displacement were calculated to determine changes in gait, and response time and accuracy were calculated to determine secondary task performance. Results indicated that older adults displayed a consistently greater step width (p ≤ 0.015) and maintained their mediolateral centre of mass displacement (p > 0.05) while walking downhill and responding to the audiospatial task, compared to downhill walking only. In contrast, younger adults maintained a regular step width during both level and downhill dual-tasking compared to level and downhill walking only (p > 0.05), however displayed a lower mediolateral centre of mass displacement during level dual-task walking compared to level walking only (p = 0.013). When the difficulty of the walking task was greater, older adults increased their step width, which increased their stability.

The metabolic power required to support body weight and accelerate body mass changes during walking on uphill and downhill slopes

The metabolic cost of walking is due to muscle force generated to support body weight (BW), external work performed to redirect and accelerate the center of mass (CoM), and internal work performed to swing the limbs and maintain balance. We hypothesized that BW support would incur a greater and lower percentage of Net Metabolic Power (NMP) for uphill and downhill slopes, respectively, compared to level-ground walking. Additionally, we hypothesized that mass redirection would incur a greater and lower percentage of NMP for uphill and downhill slopes, respectively compared to level-ground walking. 10 subjects walked at 1.25 m/s on 0°, ±3°, and ±6° slopes with reduced/added weight and added mass while we measured metabolic rates. We calculated NMP per Newton of reduced BW at each slope and found that BW support required 58% and 64% of the NMP to walk at +3° and +6°, respectively, both greater than the 15% required for level-ground walking (p < 0.025). We calculated NMP per kg of added mass at each slope and found that mass redirection required 19% and 23% of the NMP to walk at +3° and +6°, respectively, both lower than the 35% required for level-ground walking (p < 0.025). We found no significant differences in the percentage of NMP for BW support or mass redirection during downhill compared to level ground walking (p > 0.05). Our findings elucidate that the percentage of NMP attributed to BW support and mass redirection is different for sloped compared to level-ground walking. These results inform biomimetic assistive device designs aimed at reducing metabolic cost.

A Smart Terrain Identification Technique Based on Electromyography, Ground Reaction Force, and Machine Learning for Lower Limb Rehabilitation

Automatic terrain classification in lower limb rehabilitation systems has gained worldwide attention. In this field, a simple system architecture and high classification accuracy are two desired attributes. In this article, a smart neuromuscular–mechanical fusion and machine learning-based terrain classification technique utilizing only two electromyography (EMG) sensors and two ground reaction force (GRF) sensors is reported for classifying three different terrains (downhill, level, and uphill). The EMG and GRF signals from ten healthy subjects were collected, preprocessed and segmented to obtain the EMG and GRF profiles in each stride, based on which twenty-one statistical features, including 9 GRF features and 12 EMG features, were extracted. A support vector machine (SVM) machine learning model is established and trained by the extracted EMG features, GRF features and the fusion of them, respectively. Several methods or statistical metrics were used to evaluate the goodness of the proposed technique, including a paired-t-test and Kruskal–Wallis test for correlation analysis of the selected features and ten-fold cross-validation accuracy, confusion matrix, sensitivity and specificity for the performance of the SVM model. The results show that the extracted features are highly correlated with the terrain changes and the fusion of the EMG and GRF features produces the highest accuracy of 96.8%. The presented technique allows simple system construction to achieve the precise detection of outcomes, potentially advancing the development of terrain classification techniques for rehabilitation.

Psychological Responses to High-Intensity Interval Training: A Comparison of Graded Walking and Ungraded Running at Equivalent Metabolic Loads

High-intensity interval training (HIIT) is highly beneficial for health and fitness and is well tolerated. Treadmill-based HIIT normally includes running interspersed with walking. The purpose of this study was to compare ungraded running and graded walking HIIT on perceived exertion, affective valence, and enjoyment. Thirty-four active, healthy adults completed maximal testing and two 20-min HIIT trials alternating between 85% of VO2peak and a comfortable walking speed. Affective valence, enjoyment, and perceived exertion, both overall (ratings of perceived exertion [RPE]-O) and legs only (RPE-L), were measured. RPE-O and affective valence were similar between HIIT trials (p > .05), RPE-L was higher for walk HIIT (p < .05), and enjoyment was higher for run HIIT (p < .05). Findings indicate that both walk and run HIIT produce exertion, affective, and enjoyment responses that are positive and possibly supportive of exercise behavior. Walk HIIT may be desirable for individuals who are unable or do not want to run.

EFFECTS OF SINGLE CROUCH WALKING GAITS ON FATIGUE DAMAGES OF LOWER EXTREMITY MAIN MUSCLES

Single crouch walking gait (SCWG) is one of the main walking gaits when one of the legs is injured. However, the research on movement biomechanical characteristics (MBC) of lower extremity in SCWG has not been reported. So, the aim of this study is to analyze kinematics and main muscle fatigue damages of lower extremity in SCWG. Gaits data were collected with functional assessment biomechanics (FAB) system which applies the real-time wireless gait phase detection system, the movement function relations of joints of lower extremity were obtained by fitting the collected data in normal walking gait (NWG) and SCWG with Fourier series, the fitted movement functions were input to 3D human musculoskeletal model as driving functions for human movement to analyze the differences of MBC between SCWG and NWG. Finally, the muscle contractions were used to evaluate muscle fatigue damage. Compared with NWG, the result shows that the movement range of the joint angles of lower extremity are reduced in SCWG, the change law of hip internal/external rotation angle (IERA) has a significant difference, and the change laws of other joint angles are similarly between SCWG and NWG. The muscle contractions of Gluteus maximum (GMAX) 2, Gluteus meddle (GMED) 1, GMED2, Iliacus (ILI), Rectus femoris (RFEM), Soleus (SOL), Gastrocnemius (GAS) and Vastus lateralis (VLAT) are significantly larger in SCWG than in NWG (except GlutMed2 which is about 20–40% and VLAT which is about 63.8–76.1% of gait cycle), namely, these muscles easily cause muscle damages in SCWG. The contraction change of Adductor magnus (AMAG) is dispersed, so AMAG is prone to muscle fatigue in SCWG. The study results will fill in the gaps in the MBC of lower extremity in SCWG and provide data for Rehabilitation Medical Technology (RMT) and development of rehabilitation equipment of lower extremity.

Metabolic cost calculations of gait using musculoskeletal energy models, a comparison study

This paper compares predictions of metabolic energy expenditure in gait using seven metabolic energy expenditure models to assess their correlation with experimental data. Ground reaction forces, marker data, and pulmonary gas exchange data were recorded for six walking trials at combinations of two speeds, 0.8 m/s and 1.3 m/s, and three inclines, -8% (downhill), level, and 8% (uphill). The metabolic cost, calculated with the metabolic energy models was compared to the metabolic cost from the pulmonary gas exchange rates. A repeated measures correlation showed that all models correlated well with experimental data, with correlations of at least 0.9. The model by Bhargava et al. (J Biomech, 2004: 81-88) and the model by Lichtwark and Wilson (J Exp Biol, 2005: 2831-3843) had the highest correlation, 0.95. The model by Margaria (Int Z Angew Physiol Einschl Arbeitsphysiol, 1968: 339-351) predicted the increase in metabolic cost following a change in dynamics best in absolute terms.

Recumbent cycling with integrated volitional control electrical stimulation improves gait speed during the recovery stage in stroke patients

The purpose of this study was to investigate the effect of recumbent cycling with integrated volitional control electrical stimulation (IVES) on gait ability in stroke patients. Six stroke patients (all male; average age, 55.7±8.3 years) participated. Recumbent cycling (R-cycling) was performed with and without IVES in the power assist (IVES-P) mode. The targeted muscle for electrostimulation was the tibialis anterior. Patients performed 10 min of IVES-P mode plus R-cycling (program A) or R-cycling alone (program B), once per day, 5 times per week. Patients completed two sets of each program, alternating between programs each week. Gait speed and the number of steps numbers on a 10-m walking test was assessed before and after each interventional session. Program A improved gait speed, but not the number of steps, to a greater extent than that in program B. Specifically, the combined intervention significantly improved gait speed in the first set, but not the second set of the intervention. R-cycling with IVES-P mode improved gait speed during the recovery stage in stroke patients to a greater extent than that achieved with R-cycling alone. Thus, this combined therapy has potential as a standardized treatment in the field of rehabilitation medicine.

Estimation of muscle activation during different walking speeds with two mathematical approaches compared to surface EMG

BACKGROUND

Muscle force estimation could improve clinical gait analysis by enhancing insight into causes of impairments and informing targeted treatments. However, it is not currently standard practice to use muscle force models to augment clinical gait analysis, partly, because robust validations of estimated muscle activations, underpinning force modelling processes, against recorded electromyography (EMG) are lacking.

RESEARCH QUESTION

Therefore, in order to facilitate future clinical use, this study sought to validate estimated lower limb muscle activation using two mathematical models (static optimisation SO, computed muscle control CMC) against recorded muscle activations of ten healthy participants.

METHODS

Participants walked at five speeds. Visual agreement in activation onset and offset as well as linear correlation (r) and mean absolute error (MAE) between models and EMG were evaluated.

RESULTS

MAE between measured and recorded activations were variable across speeds (SO vs EMG 15-68%, CMC vs EMG 13-69%). Slower speeds resulted in smaller deviations (mean MAE < 30%) than faster speeds. Correlation was high (r > 0.5) for only 11/40 (CMC) and 6/40 (SO) conditions (muscles X speeds) compared to EMG.

SIGNIFICANCE

Modelling approaches do not yet show sufficient consistency of agreement between estimated and recorded muscle activation to support recommending immediate clinical adoption of muscle force modelling. This may be because assumptions underlying muscle activation estimations (e.g. muscles' anatomy and maximum voluntary contraction) are not yet sufficiently individualizable. Future research needs to find timely and cost efficient ways to scale musculoskeletal models for better individualisation to facilitate future clinical implementation.

Kinetic differences between level walking and ramp descent in individuals with unilateral transfemoral amputation using a prosthetic knee without a stance control mechanism

BACKGROUND

Individuals with transfemoral amputation (TFA) have difficulty in descending ramps. Although individuals with TFA who descend ramps are speculated to have greater biomechanical demands, this has not been quantified.

RESEARCH QUESTION

How do individuals with TFA wearing a prosthetic knee without a stance control mechanism adapt their gait biomechanics to a slightly declined surface?

METHODS

We retrospectively analyzed data of level walking and ramp descent (5° decline) from six subjects with TFA who used a prosthesis without a stance control mechanism. Ground reaction force and joint moment, power, and kinematics were derived from three-dimensional motion capture, combined with force measurement. Kinematic and kinetic variables were compared during level walking and ramp descent using the paired tests.

RESULTS

Compared with level walking, ramp descent increased the maximum contralateral vertical ground reaction force by 16% of the body weight, on average (standard deviation: 20%). Ramp descent tended to induce smaller concentric hip power during late swing and greater hip eccentric power on the prosthetic-side during late stance. Greater biomechanical demands during ramp descent were indicated by increased maximum medial ground reaction force on both sides, and eccentric joint power of the contralateral ankle during stance.

SIGNIFICANCE

For individuals with TFA using a prosthetic knee without a stance control mechanism, descending a ramp can increase loading on the contralateral limb during the loading response; slower walking may alleviate the effect. Ramp descent can change prosthetic-side hip muscles' control of the swinging prosthetic limb, eccentric work on the contralateral ankle plantarflexors during stance, and mediolateral balance. All of these factors should be taken into consideration when individuals with TFA learn to descend a ramp.

The Functional Roles of Muscles, Passive Prostheses, and Powered Prostheses During Sloped Walking in People With a Transtibial Amputation

Sloped walking is challenging for individuals with transtibial amputation (TTA) due to the functional loss of the ankle plantarflexors. Prostheses that actively generate ankle power may help to restore this lost function. The purpose of this study was to use musculoskeletal modeling and simulation to quantify the mechanical power delivered to body segments by passive and powered prostheses and the remaining muscles in the amputated and intact legs during sloped walking. We generated walking simulations from experimental kinematic and kinetic data on slopes of 0, ±3 deg and ±6 deg in eight people with a TTA using powered and passive prostheses and eight nonamputees. Consistent with our hypothesis, the amputated leg hamstrings generated more power to both legs on uphill slopes in comparison with nonamputees, which may have implications for fatigue or overuse injuries. The amputated leg knee extensors delivered less power to the trunk on downhill slopes (effect size (ES) ≥ 1.35, p ≤ 0.02), which may be due to muscle weakness or socket instability. The power delivered to the trunk from the powered and passive prostheses was not significantly different (p > 0.05), However, using the powered prosthesis on uphill slopes reduced the contributions from the amputated leg hamstrings in all segments (ES ≥ 0.46, p ≤ 0.003), suggesting that added ankle power reduces the need for the hamstrings to compensate for lost ankle muscle function. Neither prosthesis replaced gastrocnemius function to absorb power from the trunk and deliver it to the leg on all slopes.

Kinematic patterns while walking on a slope at different speeds

During walking, the elevation angles of the thigh, shank, and foot (i.e., the angle between the segment and the vertical) covary along a characteristic loop constrained on a plane. Here, we investigate how the shape of the loop and the orientation of the plane, which reflect the intersegmental coordination, change with the slope of the terrain and the speed of progression. Ten subjects walked on an inclined treadmill at different slopes (between -9° and +9°) and speeds (from 0.56 to 2.22 m/s). A principal component analysis was performed on the covariance matrix of the thigh, shank, and foot elevation angles. At each slope and speed, the variance accounted for by the two principal components was >99%, indicating that the planar covariation is maintained. The two principal components can be associated to the limb orientation (PC1*) and the limb length (PC2*). At low walking speeds, changes in the intersegmental coordination across slopes are characterized mainly by a change in the orientation of the covariation plane and in PC2* and to a lesser extent, by a change in PC1*. As speed increases, changes in the intersegmental coordination across slopes are more related to a change in PC1 *, with limited changes in the orientation of the plane and in PC 2*. Our results show that the kinematic patterns highly depend on both slope and speed. NEW & NOTEWORTHY In this paper, changes in the lower-limb intersegmental coordination during walking with slope and speed are linked to changes in the trajectory of the body center of mass. Modifications in the kinematic pattern with slope depend on speed: at slow speeds, the net vertical displacement of the body during each step is related to changes in limb length and orientation. When speed increases, the vertical displacement is mostly related to a change in limb orientation.

A Novel Downhill Gait-Training Program Following a Total Knee Arthroplasty: A Case Report Highlighting the Impacts of Self-selected Speed on Gait Symmetry

Study Design Case report. Background Walking plays an essential role in activities of daily living and has varied health benefits. Studies report that gait speed and symmetry are impacted in individuals following total knee arthroplasty (TKA). Unfortunately, abnormal gait patterns persist in individuals after TKA. Downhill walking may provide a simple and feasible exercise regimen to improve gait patterns. The purpose of this case report was to describe the application of a downhill treadmill training program and the subsequent changes in gait patterns in an individual following a unilateral TKA. Case Description The participant was a 59-year-old woman following a right TKA. Downhill gait training was initiated 1 month post TKA and completed for 5 weeks. Outcomes were assessed using questionnaires, mobility tests, strength of quadriceps, and gait patterns. The treadmill speed was determined by the participant's self-selected gait speed on a level surface. Outcomes The participant's eccentric quadriceps strength in the operated limb significantly increased after the gait training. Her physical function recovered to a level similar to that of previous reports. Postintervention gait analysis was conducted at 2 self-selected speeds, due to an increase in the participant's self-selected gait speed between sessions. The participant demonstrated a more symmetrical gait pattern when walking slower and a more asymmetrical gait pattern at the faster speed. Discussion After completion of downhill gait training in conjunction with therapeutic exercises, the participant showed an increase in quadriceps strength and improved physical function. This case report describes the utilization and potential feasibility of downhill gait training in conjunction with outpatient physical therapy for an individual following unilateral TKA. Level of Evidence Therapy, level 5. J Orthop Sports Phys Ther 2018;48(2):104-110. Epub 7 Nov 2017. doi:10.2519/jospt.2018.7374.

Uphill walking: Biomechanical demand on the lower extremities of obese adolescents

The number of obesity prevalence in adolescents is still increasing. Obesity treatment programs typically include physical activity with walking being recommended as appropriate activity, but limited information exists on the demand uphill walking places on the joint loading and power of obese adolescents. Therefore, the purpose of this study was to investigate the effect of different inclinations on step characteristics, sagittal and frontal joint angles, joint moments and joint power of obese adolescents in comparison to their normal-weight peers. Eleven obese (14.5±1.41 years, BMI: 31.1±3.5kg/m²) and eleven normal-weight adolescents (14.3±1.86 years, BMI: 19.0±1.7kg/m²) walked with 1.11m/s on a ramp with two imbedded force plates (AMTI, 1000Hz) at three inclinations (level, 6°, 12°). Kinematic data were collected via an infrared-camera motion system (Vicon, 250Hz). The two-way (inclination, group) ANOVA indicated a significant effect of inclination on almost all variables analysed, with the hip joint being the most affected by inclination, followed by the knee and ankle joint. The obese participants additionally spent less time in swing phase, walked with an increased knee flexion and valgus angle and an increased peak hip flexion and adduction moment. Hip joint power of obese adolescents was especially in the steepest inclination significantly increased compared to their normal-weight peers. Obese adolescents demonstrate increased joint loading compared to their normal-weight peers and in combination with a musculoskeletal malalignment they might be prone to an increased overuse injury risk.