Downhill Conditions Research Articles

Minimal toe clearance in older adults when walking on level, uphill and downhill conditions

Minimal toe clearance in older adults when walking on level, uphill and downhill conditions

Adaptive Locomotion Learning for Quadruped Robots by Combining DRL with a Cosine Oscillator Based Rhythm Controller

Animals have evolved to adapt to complex and uncertain environments, acquiring locomotion skills for diverse surroundings. To endow a robot’s animal-like locomotion ability, in this paper, we propose a learning algorithm for quadruped robots based on deep reinforcement learning (DRL) and a rhythm controller that is based on a cosine oscillator. For a quadruped robot, two cosine oscillators are utilized at the hip joint and the knee joint of one leg, respectively, and, finally, eight oscillators form the controller to realize the quadruped robot’s locomotion rhythm during moving. The coupling between the cosine oscillators of the rhythm controller is realized by the phase difference, which is simpler and easier to realize when dealing with the complex coupling relationship between different joints. DRL is used to help learn the controller parameters and, in the reward function design, we address the challenge of terrain adaptation without relying on the complex camera-based vision processing but based on the proprioceptive information, where a state estimator is introduced to achieve the robot’s posture and help finally utilize the food-end coordinate. Experiments are carried out in CoppeliaSim, and all of the flat, uphill and downhill conditions are considered. The results show that the robot can successfully accomplish all the above skills and, at the same time, with the reward function designed, the robot’s pitch angle, yaw angle and roll angle are very small, which means that the robot is relatively stable during walking. Then, the robot is transplanted to a new scene; the results show that although the environment is previously unencountered, the robot can still fulfill the task, which demonstrates the effectiveness and robustness of this proposed method.

Influence of walkway slope on single-file pedestrian flow dynamics: Results from an experimental study

Sloping walkways are common pedestrian traffic facilities in modern cities, especially, in some cities located in mountainous terrain, such as Hong Kong, and Zurich. Compared with level walkways, sloping walkways may lead to the decrease in pedestrian flow efficiency, and are more prone to trigger crowd disasters at extreme crowd densities, for example, recent crowd stampede event in Itaewon, South Korea, did happen on a narrow ramp with an extreme crowd density. Therefore, it is important to study pedestrian flow dynamics on ramps. In this paper, we conducted single-file pedestrian flow experiments in 0°, 3°, 5°, 7°, 9°, 12°, 17°, 22°, 27° uphill and downhill conditions, and analyzed contrastively the influence of walkway slope on pedestrian flow dynamics. Our main findings are as follows. (i) Pedestrian flow efficiency is the highest in 7° downhill condition, indicating that a small downhill slope is advantageous to pedestrian flowing. (ii) Whether it is uphill or downhill, the ramp steeper than 7° will significantly decrease pedestrian flow efficiency, therefore is disadvantageous to pedestrian flowing. (iii) For a ramp, uphill and downhill pedestrian flow efficiencies are not equal. Downhill pedestrian flow efficiency is always larger than uphill pedestrian flow efficiency. These findings provide important guidance for the design of sloping walkways and the safety management of pedestrian crowds on sloping walkways.

Testing and performance analysis of an integrated electromagnetic and hydraulic retarder for heavy-duty vehicles

Hydraulic retarder and eddy current retarder are important auxiliary braking component, which installed on heavy-duty vehicles. However, the hydraulic retarder has poor braking performance at low speeds, while the eddy-current retarder presents serious thermal recession at high speed. To overcome these issues and ensure safe driving during downhill conditions, a novel Integrated Electromagnetic and Hydraulic Retarder (IEHR) is proposed. The design includes a rotor with blades, double salient poles, and a coil built in a C-type stator. The electromagnetic field model of the IEHR is established and analyzed using the Finite Element Method. Moreover, the nonlinear eddy viscosity model of the flow field is generated and analyzed using the Computational Fluid Dynamics. The Blend braking control strategy is adopted to distribute the braking torque at high speed and low speed The IEHR performance was tested at a test bench. The test results show that the calculated braking characteristics of the electromagnetic and hydraulic subsystems were reasonable agreement with the measured results. The road test was carried out on a vehicle with a total mass of 49 tons. The deceleration and torque peaked at 0.75 m/s2 and 3620 N m, respectively. These results indicated that the IEHR has better performance than conventional hydraulic retarders and eddy current retarder, and is more suitable for heavy vehicles.

Changes in Distance between a Wearable Robotic Exoskeleton User and Four-Wheeled Walker during Gait in Level and Slope Conditions: Implications for Fall Prevention Systems

When walking with wearable robotic exoskeletons (WRE) in people with spinal cord injury, the distance between the user and the walker is one of the most important perspectives for ensuring safety. The purpose of this study was to clarify the distance between WRE users and four-wheeled walkers (4WW) while walking on level and sloping surfaces. To eliminate the effects of variation in neurological conditions, 12 healthy subjects participated. All participants ambulated using the WRE and the 4WW on level and sloping surfaces. The outcomes were the mean distances between the WRE users and the 4WWs in the level and slope conditions. To examine the influence of uphill and downhill slopes on distance, comparisons were conducted between the uphill or downhill conditions and the respective transitional periods. In the uphill condition, the mean distances were significantly greater than that in the level condition. Conversely, the mean distance moving downhill was significantly shorter than that in the level condition. Changes in the distance between the WRE user and the 4WW might increase the risk of falling forward on an uphill slope and backward on a downhill slope. This study’s results will assist in developing a new feedback system to prevent falls.

Effect of slope in an immersive virtual environment on segmental asymmetry in people with femoral amputation and a microprocessor knee

Purpose The continued development of microprocessor-based knee prostheses has improved the independence of people with a femoral amputation in many environments. This study aimed to describe the effect of slopes on kinematic joint variables and segmental asymmetry. Methods Ten individuals with transfemoral amputation fitted with microprocessor-controlled knees performed 5 sessions of treadmill walking at their preferred speed in an immersive virtual environment in 5 incline conditions (Level, 3° and 6° Uphill, and 3° and 6° Downhill). The Human Body Model was used to quantify kinematic joint variables from motion capture system data. The perimeter-to-area method was used to determine the symmetry ratio of the trajectory of the leg segments in the sagittal plane Results There was a significant effect of the Uphill conditions on step length and width on the intact side and on all kinematic joint variables on both sides, although the changes differed according to the phase of the gait cycle. The segmental symmetry index was significantly modified in all slope conditions compared with Level. Conclusions Kinematic joint variables are affected by slopes; the effect was greater for the Uphill than Downhill conditions compared with the Level condition. The perimeter-to-area symmetry ratio differed from the Level condition for all slope conditions. These results indicate that, although microprocessor knees improve the autonomy of prosthesis users, work is required to improve their capacity of adaptation to varied terrain to reduce kinematic asymmetry.

The movement characteristics of pedestrians on a single-file track at the uphill and downhill conditions

Ramps, as very common building structures, are widely used in railway stations, subways, shopping malls and other public places. In order to study the movement characteristics of pedestrians both uphill and downhill, we present a group of single-file movement experiments of pedestrians on a ramp with a 9° slope. It is found that in the free flow state, the average speed uphill and downhill is about 1.1 m s−1, while the average speed on the flat surface is about 1.4 m s−1. As the density increases, the critical densities at which the speed of pedestrians begins to decrease going uphill and downhill are both slightly higher than that on the flat surface. We also propose a step-based model considering different step frequencies and step lengths of pedestrians to simulate the movement on the ramp. Compared with the experimental results, it is shown that the model can reproduce the pedestrian’s walking behavior on the ramp well.

Stability characteristics and experiment of hydraulic drive four-wheel chassis

PurposeThis study aims to improve the maneuverability and stability of four-wheel chassis in a small paddy field; a front axle swing steering four-wheel chassis with optimal steering is designed.Design/methodology/approachWhen turning, the front inner wheel stops and the rear inner wheel is in the following state. The hydraulic drive system of the walking wheel adopts a driving mode in which two front-wheel motors are connected in series and two rear wheel motors in parallel. The chassis uses a combination of a gasoline engine with a water cooling system, a CVT continuously variable transmission and a hydraulic drive system to increase the control capability. The front axle rotary chassis adopts a step-less variable speed engine and a hydraulic control system to solve the hydraulic stability of the chassis in uphill and downhill conditions so as to effectively control the over-speed of the wheel-side drive motors. Through the quadratic orthogonal rotation combination design test, the mathematical models of uphill and downhill front-wheel pressures and test factors are established.FindingsThe results show that the chassis stability is optimal when the back pressure is 0.5 MPa, and the rotating slope is 4°. The uphill and downhill pressures of the front wheels are 2.38 MPa and 1.5 MPa, respectively.Originality/valueThe influence of external changes on the pressure of hydraulic motors is studied through experiments, which lays the foundation for further research.

Internal Tibial Forces and Moments During Graded Running

The stress experienced by the tibia has contributions from the forces and moments acting on the tibia. We sought to quantify the influence of running grade on internal tibial forces and moments. Seventeen participants ran at 3.33 m/s on an instrumented treadmill at 0 deg, ±5 deg, and ±10 deg while motion data were captured. Ankle joint contact force was estimated from an anthropometrically-scaled musculoskeletal model using inverse dynamics-based static optimization. Internal tibial forces and moments were quantified at the distal 1/3rd of the tibia, by ensuring static equilibrium with all applied forces and moments. Downhill running conditions resulted in lower peak internal axial force (range of mean differences: -9% to -16%, p < 0.001), lower peak internal anteroposterior force (-14% to -21%, p < 0.001), and lower peak internal mediolateral force (-14% to -15%, p < 0.001), compared to 0 deg and +5 deg. Furthermore, downhill conditions resulted in lower peak internal mediolateral moment (-11%to -21%, p < 0.001), lower peak internal anteroposterior moment (-13% to -14%, p < 0.001), and lower peak internal torsional moment (-9% to -21%, p < 0.001), compared to 0 deg, +5 deg, and +10 deg. The +10 deg condition resulted in lower peak internal axial force (-7% to -9%, p < 0.001) and lower peak internal mediolateral force (-9%, p = 0.004), compared to 0 deg and +5 deg. These findings suggest that downhill running may be associated with lower tibial stresses than either level or uphill running.

Long-term gait biomechanics in level, uphill, and downhill conditions following anterior cruciate ligament reconstruction

BackgroundAltered gait biomechanics have been linked to post-traumatic knee osteoarthritis development following anterior cruciate ligament reconstruction surgery, but the persistence of aberrant gait biomechanics after the first year post-surgery is inconsistent in the literature. Gait biomechanics are typically evaluated on a level surface, but this task may not elucidate discrepancies in individuals further removed from surgery due to the simplicity of the task. Graded surfaces are common in real-world ambulation and may exacerbate aberrant gait biomechanics due to greater mechanical demands. MethodsForty-seven individuals post-anterior cruciate ligament reconstruction (4 ± 3 years post-surgery) and forty-seven uninjured controls completed gait analysis under level, uphill, and downhill conditions on an instrumented treadmill. Outcomes included knee flexion displacement and peak knee flexion angle, vertical ground reaction force, and knee extension and abduction moments. FindingsKnee extension moment and knee flexion displacement were lesser in the surgical limb compared to the contralateral during the downhill condition, with lesser knee flexion displacement also observed during the level condition. Additionally, knee extension moment was less symmetrical in the surgical group during both uphill and downhill conditions compared to controls. Knee flexion displacement was less symmetrical in the surgical group during both level and downhill conditions compared to controls. InterpretationGraded surfaces elucidate aberrant gait biomechanics in individuals more than 1 year post-anterior cruciate ligament reconstruction that are not apparent during level walking. These findings suggest that gait assessment on level surfaces may mask existing deficiencies, and warrant emphasizing ambulation of graded surfaces during anterior cruciate ligament rehabilitation.

Changes In Gait Biomechanics Between Level And Downhill Walking Do Not Differ Between Those With Anterior Cruciate Ligament Reconstruction And Controls

Conflicting evidence exists regarding the presence of aberrant gait biomechanics after the first year post-anterior cruciate ligament reconstruction. Overground walking may not elucidate differences in those further removed from surgery due to the unexacting nature of the task. Deleterious gait biomechanics following ACLR are partly attributable to quadriceps dysfunction. Downhill walking may exacerbate aberrant gait biomechanics, as this task places greater demands on the quadriceps compared to level walking. PURPOSE: To compare gait biomechanics between individuals with ACLR and healthy controls during level and downhill walking conditions. METHODS: 24 individuals more than 1 year removed from primary ACLR (83% female, age= 21 ± 3 yr, time since ACLR 44 ± 26 mo, BMI= 23 ± 3 kg/m2) and 24 healthy controls (79% female, age= 21 ± 1 yr, BMI= 24 ± 3 kg/m2) completed both level and downhill (10°grade) gait biomechanics assessments on an instrumented split-belt treadmill at their preferred walking speed. Peak variables were evaluated over the first 50% of stance including the vertical ground reaction force (vGRF), internal knee abduction moment, internal knee extension moment, knee flexion angle, and knee abduction angle. Moments were normalized to %body weight∗height (%BW∗Ht) and vGRF was normalized to %body weight. Dependent variables were compared across groups and conditions via two-way repeated measures ANCOVA controlling for gait speed. RESULTS: There were no significant condition∗group interaction effects nor group main effects for any outcomes. However, there were significant condition main effects for peak internal knee extension moment (p = 0.020, level to downhill mean increase of 0.042 %BW∗Ht) and peak knee flexion angle (p = 0.018, level to downhill mean increase of 13.2&#176;). CONCLUSIONS: Downhill walking necessitates a larger internal extension moment and knee flexion angle compared to level gait. Our results suggest that changes in gait biomechanics between level and downhill conditions do not differ between individuals with ACLR > 1 year post reconstruction and controls. These results suggest that aberrant gait biomechanics may be mitigated over time in those with ACLR.

Study on Braking Characteristics of a Novel Eddy Current-Hydraulic Hybrid Retarder for Heavy-Duty Vehicles

Heavy-duty vehicles are generally equipped with non-contact hydraulic retarders or eddy current retarders to ensure safe driving during downhill conditions. The torque of the hydraulic retarder is large when the rotor rotates at a high speed, but the torque is small when the rotor rotates at a low speed. As another commonly used retarder, the eddy current retarder has a large torque at a low speed and a low power density at a high speed. High torque at full speed is the vehicles’ requirement for the auxiliary brake system, with no retarders can achieve this goal perfectly alone. Encouragingly, the braking performances of these two kinds of retarders are complementary. Based on the above properties, the eddy current-hydraulic hybrid retarder (EHR) is designed applying the principle of eddy current and the principle of hydraulic braking. In this novel HER, both sides of the rotor are used for hydraulic braking, and the outer ring of the rotor generates eddy currents. The finite element models of the flow field and the electromagnetic field are established separately and solved by computer to predict the braking torque of the EHR. The prototype was developed and the braking performance of the EHR was obtained through the bench tests. Comparing the theoretical calculation results and experimental data, the braking characteristics of the EHR are analyzed. At low speed, the EHR mainly relies on the eddy current braking, whereas at high speed, it relies on both eddy current and hydraulic braking. Moreover, the control of the EHR can be realized only by adjusting the braking torque of the eddy current part, which simplifies the control system.

Corticospinal excitability changes following downhill and uphill walking.

Locomotor exercise may induce corticospinal excitability and/or cortical inhibition change in the knee extensors. This study investigated whether the mode of muscle contraction involved during a locomotor exercise modulates corticospinal and intracortical responsiveness. Eleven subjects performed two 45-min treadmill walking exercises in an uphill (+ 15%) or a downhill (- 15%) condition matched for speed. Maximal voluntary isometric torque (MVIC), voluntary activation level (VAL), doublet (Dt) twitch torque, and M-wave area of the knee extensors were assessed before and after exercise. At the same time-points, motor-evoked potential (MEP), cortical silent period (CSP), and short-interval cortical inhibition (SICI) were recorded in the vastus lateralis (VL) and rectus femoris (RF) muscles. After exercise, uphill and downhill conditions induced a similar loss in MVIC torque (- 9%; p < 0.001), reduction in VAL (- 7%; p < 0.001), and in M-wave area in the VL muscle (- 8%; p < 0.001). Dt twitch torque decreased only after the downhill exercise (- 11%; p < 0.001). MEP area of the VL muscle increased after the downhill condition (p = 0.007), with no change after the uphill condition. MEP area of the RF muscle remained stable after exercises. CSP and SICI did not change in the two conditions for both muscles. Downhill walking induces an increase in MEP area of the VL muscle, with no change of the CSP duration or SICI ratio. The eccentric mode of muscle contraction during a locomotor exercise can modulate specifically corticospinal excitability in the knee extensors.

EFFECTS OF THE GENIUM MICROPROCESSOR KNEE SYSTEM ON KNEE MOMENT SYMMETRY DURING HILL WALKING.

Use of the Genium microprocessor knee (MPK) system reportedly improves knee kinematics during walking and other functional tasks compared to other MPK systems. This improved kinematic pattern was observed when walking on different hill conditions and at different speeds. Given the improved kinematics associated with hill walking while using the Genium, a similar improvement in the symmetry of knee kinetics is also feasible. The purpose of this study was to determine if Genium MPK use would reduce the degree of asymmetry (DoA) of peak stance knee flexion moment compared to the C-Leg MPK in transfemoral amputation (TFA) patients. This study used a randomized experimental crossover of TFA patients using Genium and C-Leg MPKs (n = 20). Biomechanical gait analysis by 3D motion tracking with floor mounted force plates of TFA patients ambulating at different speeds on 5° ramps was completed. Knee moment DoA was significantly different between MPK conditions in the slow and fast uphill as well as the slow and self-selected downhill conditions. In a sample of high-functioning TFA patients, Genium knee system accommodation and use improved knee moment symmetry in slow speed walking up and down a five degree ramp compared with C-Leg. Additionally, the Genium improved knee moment symmetry when walking downhill at comfortable speed. These results likely have application in other patients who could benefit from more consistent knee function, such as older patients and others who have slower walking speeds.

Relationship between Attenuation of Impact Shock at High Frequency and Flexion-Extension of the Lower Extremity Joints during Downhill Running

Objective: The purpose of this study was to determine the interrelationship between ranges of motion ofthe knee and ankle joints on the sagittal plane and the attenuation magnitude of impact shock at highfrequency (9~20 Hz) in the support phase during downhill running.Method: Fifteen male heel-toe runners with no history of lower extremity injuries were recruited for thisstudy (age, 25.07 ± 5.35 years; height, 175.4 ± 4.6 cm; mass, 75.8 ± .70 kg). Two uniaxial accelerometers weremounted to the tuberosity of tibia and sacrum, respectively, to measure acceleration signals. The participantswere asked to run at their preferred running speed on a treadmill set at 0°, 7°, and 15° downhill. Sixoptical cameras were placed around the treadmill to capture the coordinates of the joints of the lowerextremities. The power spectrum densities of the two acceleration signals were analyzed and used in thetransfer function describing the gain and attenuation of impact shock between the tibia and the sacrum.Angles of the knee and ankle joints on the sagittal plane and their angle ranges were calculated. ThePearson correlation coefficient was used to test the relationship between two variables, the magnitude ofimpact shock, and the range of joint angle under three downhill conditions. The alpha level was set at .05.Results: Close correlations were observed between the knee joint range of motion and the attenuationmagnitude of impact shock regardless of running slopes (p<.05), and positive correlations were foundbetween the ranges of motion of the knee and ankle joints and the attenuation magnitude of impact shockin 15° downhill running (p<.05).Conclusion: In conclusion, increased knee flexion might be required to attenuate impact shock duringdownhill and level running through change in stride or cadence while maintaining stability, and strongand flexible ankle joints are also needed in steeper downhill running.

Lower limb joint angles and ground reaction forces in forefoot strike and rearfoot strike runners during overground downhill and uphill running

This study investigated the normal and parallel ground reaction forces during downhill and uphill running in habitual forefoot strike and habitual rearfoot strike (RFS) runners. Fifteen habitual forefoot strike and 15 habitual RFS recreational male runners ran at 3 m/s ± 5% during level, uphill and downhill overground running on a ramp mounted at 6° and 9°. Results showed that forefoot strike runners had no visible impact peak in all running conditions, while the impact peaks only decreased during the uphill conditions in RFS runners. Active peaks decreased during the downhill conditions in forefoot strike runners while active loading rates increased during downhill conditions in RFS runners. Compared to the level condition, parallel braking peaks were larger during downhill conditions and parallel propulsive peaks were larger during uphill conditions. Combined with previous biomechanics studies, our findings suggest that forefoot strike running may be an effective strategy to reduce impacts, especially during downhill running. These findings may have further implications towards injury management and prevention.

Effects of Increasing or Decreasing Cadence on Metabolic, Cardiopulmonary and Biomechanical Responses During Downhill Running

PURPOSE: Running races are becoming popular in geographic areas with hilly terrain. This study compared the collective metabolic, cardiopulmonary and biomechanical responses during acute downhill and level running. METHODS:This study used a repeated-measures, crossover design in healthy runners (N=30; 28.6±8.6yrs, 21.6±1.9kg/m2). Each runner completed six conditions including level running at self-selected cadence, and downhill running (-6% grade) at five cadences (self-selected, ±5% and ±10%). A portable gas analyzer and heart rate monitor collected energy cost, minute ventilation (Ve), rate of oxygen use (VO2), heart rate (HR). 3D motion analysis and an instrumented treadmill were used to determine temporalspatial parameters, peak ground reaction forces (GRF) and lower extremity joint powers. RESULTS: During the downhill conditions, Ve increased (61.1 to 65.6 L/min; p=.017) and HR increased (141 to 151 bpm; p=.010) from fastest cadence to slowest cadence, with no difference in energy cost or VO2 among the conditions (both p>.05). As cadence increased among the downhill conditions, step length decreased and step width increased (both p<.05). GRF values progressively increased in the downhill conditions from fastest to slowest cadence (16.7 to 17.5 Nm; p=.029). Among ankle, knee and hip powers, knee power values increased from fastest to slowest cadence (9.5 to 12.2 Watts; p=.023). CONCLUSIONS: When compared to the control condition, running downhill with a progressively faster cadence increases cardiopulmonary and biomechanical responses, but not metabolic responses. The findings suggest that runners maintain energetic cost among different cadence conditions by making adjustments to muscle activation patterns when running downhill. This muscle recruitment concept could be tested using similar cadence conditions described here during flat, uphill and downhill running.

Geckos decouple fore- and hind limb kinematics in response to changes in incline.

BackgroundTerrestrial animals regularly move up and down surfaces in their natural habitat, and the impacts of moving uphill on locomotion are commonly examined. However, if an animal goes up, it must go down. Many morphological features enhance locomotion on inclined surfaces, including adhesive systems among geckos. Despite this, it is not known whether the employment of the adhesive system results in altered locomotor kinematics due to the stereotyped motions that are necessary to engage and disengage the system. Using a generalist pad-bearing gecko, Chondrodactylus bibronii, we determined whether changes in slope impact body and limb kinematics.ResultsDespite the change in demand, geckos did not change speed on any incline. This constant speed was achieved by adjusting stride frequency, step length and swing time. Hind limb, but not forelimb, kinematics were altered on steep downhill conditions, thus resulting in significant de-coupling of the limbs.ConclusionsUnlike other animals on non-level conditions, the geckos in our study only minimally alter the movements of distal limb elements, which is likely due to the constraints associated with the need for rapid attachment and detachment of the adhesive system. This suggests that geckos may experience a trade-off between successful adhesion and the ability to respond dynamically to locomotor perturbations.

Energy cost and kinematics of level, uphill and downhill running: fatigue-induced changes after a mountain ultramarathon

This study aimed to determine whether the fatigue induced by a mountain ultramarathon (MUM) led to changes in energy cost and kinematic during level and graded running. Pre- and post-race, 14 ultratrail runners ran on a level, uphill (5%) and downhill (5%) treadmill at 10 km · h−1. Kinematic data were acquired using a photocell system. Post-race, the downhill energy cost increased by 13.1% (P < 0.001). No change was noted in level and uphill running. Duty factor and stride frequency were increased, whereas swing time, cycle time and stride length were decreased in all conditions (P < 0.05). Contact time was increased and the rate of force generation was decreased only in the uphill and downhill conditions (P < 0.05). Positive correlations were observed between performance time and the pre- to post-changes in the energy cost of level (r = 0.52, P = 0.04) and uphill running (r = 0.50, P = 0.04). MUM-induced fatigue resulted in physiological and spatiotemporal changes, though the response to fatigue varied considerably between running conditions. These changes resulted in a significant increment only in the downhill energy cost. Incorporating downhill locomotion in the training programmes of ultratrailers may help to improve performance-related physiological and biomechanical parameters.

Energy Expenditure And Comfort During Nordic Walking And Ordinary Walking

It is a characteristic of Nordic Walking that energy expenditure is greater during this fitness activity than during ordinary walking. As much as 23% greater energy expenditure has been reported. The amount of extra energy expenditure during Nordic Walking most likely depends on how vigorously the Nordic Walking is performed. However for another important characteristic of fitness exercise, it is unknown how comfort compares for Nordic Walking and ordinary walking. PURPOSE: To compare energy expenditure and comfort during Nordic Walking and ordinary walking. METHODS: Twelve participants (mean±SEM: 171.5±1.5 cm, 67.0±2.7 kg, 50.6±2.4 years, maximal oxygen uptake of 43.4±2.8 ml kg-1 min-1) performed 6-min bouts of uphill (12°), downhill (12°), and horizontal Nordic Walking as well as ordinary walking on a motorized treadmill with their preferred pole length of 67.6±0.6% of body height. Energy expenditure was calculated from measured oxygen uptake while comfort was self-rated on a 1- to 10-point scale where 1 and 10 corresponded to "very, very uncomfortable" and "very, very comfortable", respectively. RESULTS: Nordic Walking required as much as 65±12% greater energy expenditure (p<0.05) than ordinary walking with the greatest difference observed for the horizontal condition. During uphill and downhill conditions, energy expenditure for Nordic Walking was 8±2% and 55±12% higher, respectively (p<0.05). Nevertheless, comfort was similar for the two types of locomotion for each slope (p>0.05). Illustrating the peculiarity of Nordic Walking, comfort was 7.3±0.6 at the same time as participants exercised at more than 85% of their maximal oxygen uptake during uphill Nordic Walking. CONCLUSION: Comfort responses were generally high and at the same time similar for Nordic Walking and ordinary walking for each slope condition despite greater energy expenditure during Nordic Walking. The substantially larger energy expenditure of Nordic Walking compared to previous studies reflects the particularly vigorous Nordic Walking technique used here. From a physical activity and public health perspective it is noteworthy that Nordic Walking (vs. other forms of physical activity, e.g. running) is comfortable and apparently gentle on the body for many people, even when performed at a considerable cardiovascular load.