Horizontal running inside circular walls of Moon settlements: a comprehensive countermeasure for low-gravity deconditioning?

Long-lasting exposure to low gravity, such as in lunar settlements planned by the ongoing Artemis Program, elicits muscle hypotrophy, bone demineralization, cardio-respiratory and neuro-control deconditioning, against which optimal countermeasures are still to be designed. Rather than training selected muscle groups only, 'whole-body' activities such as locomotion seem better candidates, but at Moon gravity both 'pendular' walking and bouncing gaits like running exhibit abnormal dynamics at faster speeds. We theoretically and experimentally show that much greater self-generated artificial gravities can be experienced on the Moon by running horizontally inside a static 4.7 m radius cylinder (motorcyclists' 'Wall of Death' of amusement parks) at speeds preventing downward skidding. To emulate lunar gravity, 83% of body weight was unloaded by pre-tensed (36 m) bungee jumping bands. Participants unprecedentedly maintained horizontal fast running (5.4-6.5 m s-1) for a few circular laps, with intense metabolism (estimated as 54-74 mlO2 kg-1 min-1) and peak forces during foot contact, inferred by motion analysis, of 2-3 Earth body weight (corresponding to terrestrial running at 3-4 m s-1), high enough to prevent bone calcium resorption. A training regime of a few laps a day promises to be a viable countermeasure for astronauts to quickly combat whole-body deconditioning, for further missions and home return.

The work to swing limbs in humans versus chimpanzees and its relation to the metabolic cost of walking.

Compared to their closest ape relatives, humans walk bipedally with lower metabolic cost (C) and less mechanical work to move their body center of mass (external mechanical work, WEXT). However, differences in WEXT are not large enough to explain the observed lower C: humans may also do less work to move limbs relative to their body center of mass (internal kinetic mechanical work, WINT,k). From published data, we estimated differences in WINT,k, total mechanical work (WTOT), and efficiency between humans and chimpanzees walking bipedally. Estimated WINT,k is ~ 60% lower in humans due to changes in limb mass distribution, lower stride frequency and duty factor. When summing WINT,k to WEXT, between-species differences in efficiency are smaller than those in C; variations in WTOT correlate with between-species, but not within-species, differences in C. These results partially support the hypothesis that the low cost of human walking is due to the concerted low WINT,k and WEXT.

Metabolic cost and mechanical work of walking in a virtual reality emulator.

PURPOSE: The purpose of this study was to investigate the metabolic cost (C), mechanical work, and kinematics of walking on a multidirectional treadmill designed for locomotion in virtual reality. METHODS: Ten participants (5 females, body mass 67.2 ± 8.1 kg, height 1.71 ± 0.07 m, age 23.6 ± 1.9 years, mean ± SD) walked on a Virtuix Omni multidirectional treadmill at four imposed stride frequencies: 0.70, 0.85, 1.00, and 1.15 Hz. A portable metabolic system measured oxygen uptake, enabling calculation of C and the metabolic equivalent of task (MET). Gait kinematics and external, internal, and total mechanical work (WTOT) were calculated by an optoelectronic system. Efficiency was calculated either as WTOT/C or by summing WTOT to the work against sliding frictions. Results were compared with normal walking, running, and skipping. RESULTS: C was higher for walking on the multidirectional treadmill than for normal walking, running, and skipping, and decreased with speed (best-fit equation: C = 20.2-27.5·speed + 15.8·speed2); the average MET was 4.6 ± 1.4. Mechanical work was higher at lower speeds, but similar to that of normal walking at higher speeds, with lower pendular energy recovery and efficiency; differences in efficiency were explained by the additional work against sliding frictions. At paired speeds, participants showed a more forward-leaned trunk and higher ankle dorsiflexion, stride frequency, and duty factor than normal walking. CONCLUSION: Walking on a multidirectional treadmill requires a higher metabolic cost and different mechanical work and kinematics than normal walking. This raises questions on its use for gait rehabilitation but highlights its potential for high-intensity exercise and physical activity promotion.

Movement in low gravity environments (MoLo) programme-The MoLo-L.O.O.P. study protocol.

BACKGROUND: Exposure to prolonged periods in microgravity is associated with deconditioning of the musculoskeletal system due to chronic changes in mechanical stimulation. Given astronauts will operate on the Lunar surface for extended periods of time, it is critical to quantify both external (e.g., ground reaction forces) and internal (e.g., joint reaction forces) loads of relevant movements performed during Lunar missions. Such knowledge is key to predict musculoskeletal deconditioning and determine appropriate exercise countermeasures associated with extended exposure to hypogravity. OBJECTIVES: The aim of this paper is to define an experimental protocol and methodology suitable to estimate in high-fidelity hypogravity conditions the lower limb internal joint reaction forces. State-of-the-art movement kinetics, kinematics, muscle activation and muscle-tendon unit behaviour during locomotor and plyometric movements will be collected and used as inputs (Objective 1), with musculoskeletal modelling and an optimisation framework used to estimate lower limb internal joint loading (Objective 2). METHODS: Twenty-six healthy participants will be recruited for this cross-sectional study. Participants will walk, skip and run, at speeds ranging between 0.56-3.6 m/s, and perform plyometric movement trials at each gravity level (1, 0.7, 0.5, 0.38, 0.27 and 0.16g) in a randomized order. Through the collection of state-of-the-art kinetics, kinematics, muscle activation and muscle-tendon behaviour, a musculoskeletal modelling framework will be used to estimate lower limb joint reaction forces via tracking simulations. CONCLUSION: The results of this study will provide first estimations of internal musculoskeletal loads associated with human movement performed in a range of hypogravity levels. Thus, our unique data will be a key step towards modelling the musculoskeletal deconditioning associated with long term habitation on the Lunar surface, and thereby aiding the design of Lunar exercise countermeasures and mitigation strategies.

Rocker-profile design shoes improve pendular energy recovery in walking with no effects on total mechanical work.

Rocker-profile design shoes are commonly used in clinical settings. Such footwear reduces in-shoe pressure over the forefoot area during the gait, and depending on the rocker-profile type (i.e., toe-only, heel negative, or double rocker), affects lower limb kinematics, kinetics, and muscle electromyographic activity. However, whether wearing rocker-profile shoes influence the dynamics of the body centre of mass (BCoM) is unknown. We used a mathematical procedure combining Lissajous contours and Fourier analysis to describe the 3D trajectory of the BCoM in walking with rocker-profile (RollingSole) and flat (Control) shoes at 0.97, 1.25, and 1.53 m s-1 in 30 participants. Harmonics amplitude and phase were compared using linear and circular statistics, respectively. External (Wext), kinematic internal (Wint,k) and total (Wtot) mechanical works, and the mechanical energy fraction recovered from a pendular exchange of potential and kinetic energy were also calculated. RollingSole shoes yielded greater Wext (1-9 %; P < 0.05) and fractional pendular energy exchange (1-8 %; P < 0.01), with lower Wint,k (2-5 %; P < 0.05) and unchanged Wtot (P ≥ 0.30). RollingSole shoes led also to a greater mean height of the BCoM (1-3 %; P < 0.01), and amplitude of the anteroposterior and vertical symmetric, and mediolateral 2nd-to-5th harmonics (1-30 %; P < 0.01). No differences between shoes were found for the harmonics phase (P ≥ 0.14). Our results indicate that RollingSole shoes enhanced an inverted pendulum-like behaviour of the BCoM during walking with no alterations in total mechanical work. This may result from the combination of rocker-profile design and greater BCoM height (through thicker soles) with such shoes, increasing recovery of mechanical energy in step-to-step transitions and mid-stance.

Inertial biometry from commercial 3D body meshes.

Body segments inertial parameters (or, more generally encompassing humans and animal species, inertial biometry), often necessary in kinetics calculations, have been obtained in the past from cadavers, medical 3D imaging, 3D scanning, or geometric approximations. This restricted the inertial archives to a few species. The methodology presented here uses commercial 3D meshes of human and animal bodies, which can be further re-shaped and 'posed', according to an underlying skeletal structure, before processing. The sequence of steps from virtually chopping the mesh to the estimation of inertial parameters of body segments is described. The accuracy of the method is tested by comparing the estimated results to real data published for humans (male and female), horses, and domestic cats. The proposed procedure opens the possibility of remarkably expanding biomechanics research when body size and shape change, or when external tools, such as prosthesis and sport material, take part in biological movement.

Mechanical work as a (key) determinant of energy cost in human locomotion: recent findings and future directions.

NEW FINDINGS: What is the topic of this review? This narrative review explores past and recent findings on the mechanical determinants of energy cost during human locomotion, obtained by using a mechanical approach based on König's theorem (Fenn's approach). What advances does it highlight? Developments in analytical methods and their applications allow a better understanding of the mechanical-bioenergetic interaction. Recent advances include the determination of 'frictional' internal work; the association between tendon work and apparent efficiency; a better understanding of the role of energy recovery and internal work in pathological gait (amputees, stroke and obesity); and a comprehensive analysis of human locomotion in (simulated) low gravity conditions. ABSTRACT: During locomotion, muscles use metabolic energy to produce mechanical work (in a more or less efficient way), and energetics and mechanics can be considered as two sides of the same coin, the latter being investigated to understand the former. A mechanical approach based on König's theorem (Fenn's approach) has proved to be a useful tool to elucidate the determinants of the energy cost of locomotion (e.g., the pendulum-like model of walking and the bouncing model of running) and has resulted in many advances in this field. During the past 60 years, this approach has been refined and applied to explore the determinants of energy cost and efficiency in a variety of conditions (e.g., low gravity, unsteady speed). This narrative review aims to summarize current knowledge of the role that mechanical work has played in our understanding of energy cost to date, and to underline how recent developments in analytical methods and their applications in specific locomotion modalities (on a gradient, at low gravity and in unsteady conditions) and in pathological gaits (asymmetric gait pathologies, obese subjects and in the elderly) could continue to push this understanding further. The recent in vivo quantification of new aspects that should be included in the assessment of mechanical work (e.g., frictional internal work and elastic contribution) deserves future research that would improve our knowledge of the mechanical-bioenergetic interaction during human locomotion, as well as in sport science and space exploration.

Frictional internal work of damped limbs oscillation in human locomotion.

Joint friction has never previously been considered in the computation of mechanical and metabolic energy balance of human and animal (loco)motion, which heretofore included just muscle work to move the body centre of mass (external work) and body segments with respect to it. This happened mainly because, having been previously measured ex vivo, friction was considered to be almost negligible. Present evidences of in vivo damping of limb oscillations, motion captured and processed by a suited mathematical model, show that: (a) the time course is exponential, suggesting a viscous friction operated by the all biological tissues involved; (b) during the swing phase, upper limbs report a friction close to one-sixth of the lower limbs; (c) when lower limbs are loaded, in an upside-down body posture allowing to investigate the hip joint subjected to compressive forces as during the stance phase, friction is much higher and load dependent; and (d) the friction of the four limbs during locomotion leads to an additional internal work that is a remarkable fraction of the mechanical external work. These unprecedented results redefine the partitioning of the energy balance of locomotion, the internal work components, muscle and transmission efficiency, and potentially readjust the mechanical paradigm of the different gaits.

A slow V̇O2 on-response allows comfortable adoption of aerobically unaffordable walking and running speeds on short stair ascents.

The aim of this study was to investigate the mechanical and metabolic reasons for the spontaneous gait/speed choice when ascending a short flight of stairs, where walking on every step or running on every other step are frequently interchangeable options. The kinematics, oxygen uptake (V̇O2 ), ventilation and heart rate of 24 subjects were sampled during climbing one and two flights of stairs while using the two gaits. Although motor acts were very short in time (5-22 s), metabolic kinetics, extending into the 250 s after the end of climbing, consistently reflected the (metabolic equivalent of the) required mechanical energy and allowed comparison of the two ascent choices: despite a 250% higher mechanical power associated with running, measured [Formula: see text], ventilation and heart rate peaked at only +25% with respect to walking, and in both gaits at much lower values than [Formula: see text] despite predictions based on previous gradient locomotion studies. Mechanical work and metabolic cost of transport, as expected, showed a similar increase (+25%) in running. For stairs up to a height of 4.8 m (30 steps at 53% gradient), running makes us consume slightly more calories than walking, and in both gaits with no discomfort at all. The cardio-respiratory-metabolic responses similarly delay and dampen the replenishment of phosphocreatine stores, which were depleted much faster during the impulsive, highly powered mechanical event, with almost overlapping time courses. This discrepancy between mechanical and metabolic dynamics allows us to afford climbs ranging from almost to very anaerobic, and to interchangeably decide whether to walk or run up a short flight of stairs.

A slow V̇O2 on-response allows to comfortably adopt aerobically unaffordable walking and running speeds in short stairs ascending.

The aim of this paper is to investigate the mechanical and metabolic reasons of the spontaneous gait/speed choice of ascending short flight of stairs, where walking on every step or running on every other step are frequently interchangeable options. Twenty-four subjects' kinematics, oxygen uptake (V̇O2), ventilation and heart rate were sampled during climbing one and two flights of stairs while using the two gaits. Although motor acts were very short in time (5-22 s), metabolic kinetics, extending in the successive 250 s after the end of climbing, consistently reflected the (equivalent of the) needed mechanical energy and allowed to compare the two ascent choices: despite a 250% higher mechanical power associated to running, measured V̇O2, ventilation and heart rate peaked only at +25% with respect to walking, and in both gaits at a much lower values than V̇O2max despite of predictions based on previous gradient locomotion studies. Mechanical work and metabolic cost of transport, as expected, showed similar increase (+25%) in running. For stairs up to 4.8 m tall (30 steps at 53% gradient), running makes us consuming slightly more calories than walking, and in both gaits at no discomfort at all. The cardio-respiratory-metabolic responses similarly delay and damp the replenishing of phosphocreatine stores, which were much faster depleted during the impulsive, highly powered mechanical event, with almost overlapping time courses. Such a discrepancy between mechanical and metabolic dynamics allows to afford almost-to-very anaerobic climbs and to interchangeably decide whether to walk or run up a short flight of stairs.

Comprehensive mechanical power analysis in sprint running acceleration.

Sprint running is a common feature of many sport activities. The ability of an athlete to cover a distance in the shortest time relies on his/her power production. The aim of this study was to provide an exhaustive description of the mechanical determinants of power output in sprint running acceleration and to check whether a predictive equation for internal power designed for steady locomotion is applicable to sprint running acceleration. Eighteen subjects performed two 20 m sprints in a gym. A 35-camera motion capture system recorded the 3D motion of the body segments and the body center of mass (BCoM) trajectory was computed. The mechanical power to accelerate and rise BCoM (external power, Pext ) and to accelerate the segments with respect to BCoM (internal power, Pint ) was calculated. In a 20 m sprint, the power to accelerate the body forward accounts for 50% of total power; Pint accounts for 41% and the power to rise BCoM accounts for 9% of total power. All the components of total mechanical power increase linearly with mean sprint velocity. A published equation for Pint prediction in steady locomotion has been adapted (the compound factor q accounting for the limbs' inertia decreases as a function of the distance within the sprint, differently from steady locomotion) and is still able to predict experimental Pint in a 20 m sprint with a bias of 0.70 ± 0.93 W kg-1 . This equation can be used to include Pint also in other methods that estimate external horizontal power only.

Mechanical work in shuttle running as a function of speed and distance: Implications for power and efficiency.

Biomechanics (and energetics) of human locomotion are generally studied at constant, linear, speed whereas less is known about running mechanics when velocity changes (because of accelerations, decelerations or changes of direction). The aim of this study was to calculate mechanical work and power and to estimate mechanical efficiency in shuttle runs (as an example of non-steady locomotion) executed at different speeds and over different distances. A motion capture system was utilised to record the movements of the body segments while 20 athletes performed shuttle runs (with a 180° change of direction) at three paces (slow, moderate and maximal) and over four distances (5, 10, 15 and 20 m). Based on these data the internal, external and total work of shuttle running were calculated as well as mechanical power; mechanical efficiency was then estimated based on values of energy cost reported in the literature. Total mechanical work was larger the faster the velocity and the shorter the distance covered (range: 2.3-3.7 J m-1 kg-1) whereas mechanical efficiency showed an opposite trend (range: 0.20-0.50). At maximal speed, over all distances, braking/negative power (about 21 W kg-1) was twice the positive power. Present results highlight that running humans can exert a larger negative than positive power, in agreement with the fundamental proprieties of skeletal muscles in vivo. A greater relative importance of the constant speed phase, associated to a better exploitation of the elastic energy saving mechanism, is likely responsible of the higher efficiency at the longer shuttle distances.

Energy cost of ambulation in trans-tibial amputees using a dynamic-response foot with hydraulic versus rigid 'ankle': insights from body centre of mass dynamics.

BACKGROUND: Previous research has shown that use of a dynamic-response prosthetic foot (DRF) that incorporates a small passive hydraulic ankle device (hyA-F), provides certain biomechanical benefits over using a DRF that has no ankle mechanism (rigA-F). This study investigated whether use of a hyA-F in unilateral trans-tibial amputees (UTA) additionally provides metabolic energy expenditure savings and increases the symmetry in walking kinematics, compared to rigA-F. METHODS: Nine active UTA completed treadmill walking trials at zero gradient (at 0.8, 1.0, 1.2, 1.4, and 1.6 of customary walking speed) and for customary walking speed only, at two angles of decline (5° and 10°). The metabolic cost of locomotion was determined using respirometry. To gain insights into the source of any metabolic savings, 3D motion capture was used to determine segment kinematics, allowing body centre of mass dynamics (BCoM), differences in inter-limb symmetry and potential for energy recovery through pendulum-like motion to be quantified for each foot type. RESULTS: During both level and decline walking, use of a hyA-F compared to rigA-F significantly reduced the total mechanical work and increased the interchange between the mechanical energies of the BCoM (recovery index), leading to a significant reduction in the metabolic energy cost of locomotion, and hence an associated increase in locomotor efficiency (p < 0.001). It also increased inter-limb symmetry (medio-lateral and progression axes, particularly when walking on a 10° decline), highlighting the improvements in gait were related to a lessening of the kinematic compensations evident when using the rigA-F. CONCLUSIONS: Findings suggest that use of a DRF that incorporates a small passive hydraulic ankle device will deliver improvements in metabolic energy expenditure and kinematics and thus should provide clinically meaningful benefits to UTAs' everyday locomotion, particularly for those who are able to walk at a range of speeds and over different terrains.

Update and extension of the 'equivalent slope' of speed-changing level locomotion in humans: a computational model for shuttle running.

Controlled experimental protocols for metabolic cost assessment of speed-changing locomotion are quite complex to design and manage. The use of the 'equivalent slope', i.e. the gradient locomotion at constant speed metabolically equivalent to a level progression in acceleration, has proved valuable in the estimation of the metabolic cost of speed-changing gaits. However, its use with steep slopes requires extrapolation of the experimental cost versus gradient function for constant running speed, resulting in less-reliable estimates. The present study extended the model to also work with deceleration, and revised the predictive equation to enable it to be applied to much higher levels of speed change. Shuttle running at different distances (from 5+5 to 20+20 m) was then investigated using the novel approach and software, and the predictions in terms of metabolic cost and efficiency compare well with the experimental data.

A "Wearable" Test for Maximum Aerobic Power: Real-Time Analysis of a 60-m Sprint Performance and Heart Rate Off-Kinetics.

Maximum aerobic power ([Formula: see text]) as an indicator of body fitness is today a very well-known concept not just for athletes but also for the layman. Unfortunately, the accurate measurement of that variable has remained a complex and exhaustive laboratory procedure, which makes it inaccessible to many active people. In this paper we propose a quick estimate of it, mainly based on the heart rate off-kinetics immediately after an all-out 60-m sprint run. The design of this test took into account the recent availability of wrist wearable, heart band free, multi-sensor smart devices, which could also inertially detect the different phases of the sprint and check the distance run. 25 subjects undertook the 60-m test outdoor and a [Formula: see text] test on the laboratory treadmill. Running average speed, HR excursion during the sprint and the time constant (τ) of HR exponential decay in the off-kinetics were fed into a multiple regression, with measured [Formula: see text] as the dependent variable. Statistics revealed that within the investigated range (25-55 ml O2/(kg min)), despite a tendency to overestimate low values and underestimate high values, the three predictors confidently estimate individual [Formula: see text] (R2 = 0.65, p < 0.001). The same analysis has been performed on a 5-s averaged time course of the same measured HR off-kinetics, as these are the most time resolved data for HR provided by many modern smart watches. Results indicate that despite of the substantial reduction in sample size, predicted [Formula: see text] still explain 59% of the variability of the measured [Formula: see text].

On the Estimation Accuracy of the 3D Body Center of Mass Trajectory during Human Locomotion: Inverse vs. Forward Dynamics.

The dynamics of body center of mass (BCoM) 3D trajectory during locomotion is crucial to the mechanical understanding of the different gaits. Forward Dynamics (FD) obtains BCoM motion from ground reaction forces while Inverse Dynamics (ID) estimates BCoM position and speed from motion capture of body segments. These two techniques are widely used by the literature on the estimation of BCoM. Despite the specific pros and cons of both methods, FD is less biased and considered as the golden standard, while ID estimates strongly depend on the segmental model adopted to schematically represent the moving body. In these experiments a single subject walked, ran, (uni- and bi-laterally) skipped, and race-walked at a wide range of speeds on a treadmill with force sensors underneath. In all conditions a simultaneous motion capture (8 cameras, 36 markers) took place. 3D BCoM trajectories computed according to five marker set models of ID have been compared to the one obtained by FD on the same (about 2,700) strides. Such a comparison aims to check the validity of the investigated models to capture the "true" dynamics of gaits in terms of distance between paths, mechanical external work and energy recovery. Results allow to conclude that: (1) among gaits, race walking is the most critical in being described by ID, (2) among the investigated segmental models, those capturing the motion of four limbs and trunk more closely reproduce the subtle temporal and spatial changes of BCoM trajectory within the strides of most gaits, (3) FD-ID discrepancy in external work is speed dependent within a gait in the most unsuccessful models, and (4) the internal work is not affected by the difference in BCoM estimates.

Mechanical work and efficiency of 5 + 5 m shuttle running.

PURPOSE: Acceleration and deceleration phases characterise shuttle running (SR) compared to constant speed running (CR); mechanical work is thus expected to be larger in the former compared to the latter, at the same average speed (v mean). The aim of this study was to measure total mechanical work (W tot (+) , J kg(-1) m(-1)) during SR as the sum of internal (W int (+) ) and external (W ext (+) ) work and to calculate the efficiency of SR. METHODS: Twenty males were requested to perform shuttle runs over a distance of 5 + 5 m at different speeds (slow, moderate and fast) to record kinematic data. Metabolic data were also recorded (at fast speed only) to calculate energy cost (C, J kg(-1) m(-1)) and mechanical efficiency (eff(+) = W tot (+) C (-1)) of SR. RESULTS: Work parameters significantly increased with speed (P < 0.001): W ext (+)  = 1.388 + 0.337 v mean; W int (+)  = -1.002 + 0.853 v mean; W tot (+)  = 1.329 v mean. At the fastest speed C was 27.4 ± 2.6 J kg(-1) m(-1) (i.e. about 7 times larger than in CR) and eff(+) was 16.2 ± 2.0 %. CONCLUSIONS: W ext (+) is larger in SR than in CR (2.5 vs. 1.4 J kg(-1) m(-1) in the range of investigated speeds: 2-3.5 m s(-1)) and W int (+) , at fast speed, is about half of W tot (+) . eff(+) is lower in SR (16 %) than in CR (50-60 % at comparable speeds) and this can be attributed to a lower elastic energy reutilization due to the acceleration/deceleration phases over this short shuttle distance.

Hopping locomotion at different gravity: metabolism and mechanics in humans.

Previous literature on the effects of low gravity on the mechanics and energetics of human locomotion already dealt with walking, running, and skipping. The aim of the present study is to obtain a comprehensive view on that subject by including measurements of human hopping in simulated low gravity, a gait often adopted in many Apollo Missions and documented in NASA footage. Six subjects hopped at different speeds at terrestrial, Martian, and Lunar gravity on a treadmill while oxygen consumption and 3D body kinematic were sampled. Results clearly indicate that hopping is too metabolically expensive to be a sustainable locomotion on Earth but, similarly to skipping (and running), its economy greatly (more than ×10) increases at lower gravity. On the Moon, the metabolic cost of hopping becomes even lower than that of walking, skipping, and running, but the general finding is that gaits with very different economy on Earth share almost the same economy on the Moon. The mechanical reasons for such a decrease in cost are discussed in the paper. The present data, together with previous findings, will allow also to predict the aerobic traverse range/duration of astronauts when getting far from their base station on low gravity planets.