Physiological and Biomechanical Responses to Running on Lower Body Positive Pressure Treadmills in Healthy Populations

Are anti-gravity treadmills reliable to explore exercise energy metabolism at low degrees of alleviation in normal-weight male individuals?

BACKGROUND

Exploring the independent effect of mechanical discharge in response to weight loss (WL) seems necessary but remains highly challenging from a methodological point. Anti-gravity treadmills could be relevant to simulate a mechanical WL by body weight support (BWS), but their reliability remains unclear to properly explore exercise energy metabolism, especially at low degrees of alleviations.

OBJECTIVE

The study aimed to evaluate the accuracy and reproducibility of an anti-gravity treadmill to generate BWS, and the reproducibility of cardiometabolic responses to an exercise performed at low degrees of BWS on this device.

METHODS

Observed BWS of 18 normal-weight males was obtained twice at seven degrees of target BWS (i.e., 0, 3, 6, 9, 12, 15, 18%) using a digital scale inside the anti-gravity treadmill, and was compared to the expected BWS. Then, 15 of them performed 5-min bout of low-intensity walking exercise at these degrees of BWS in a randomized order, separated by 4-min rest. The exercise was identically repeated on three occasions separated by a minimum of 3 days. Energy metabolism and heart rate (HR) were measured throughout the exercise by indirect calorimetry and a HR monitor, respectively.

RESULTS

The observed BWS were significantly different from the expected BWS (p< 0.001), and there was a high inter- and intra-individual variability in BWS generated by the anti-gravity treadmill. Results showed an overall good reliability of VO2 (intraclass correlation coefficients (ICC) values ranging from 0.67 to 0.85) and HR (ICC > 0.8) in response to exercise. An effect of the degree of BWS was observed for VO2 (p< 0.001), illustrating reduced values at 15% and 18% of BWS compared to 0, 3, and 6%.

CONCLUSIONS

Such device might not be adapted to simulate low degrees of WL in normal-weight males, particularly when it comes to the exploration of energy metabolism.

Muscle synergies inherent in simulated hypogravity running reveal flexible but not unconstrained locomotor control

With human space exploration back in the spotlight, recent studies have investigated the neuromuscular adjustments to simulated hypogravity running. They have examined the activity of individual muscles, whereas the central nervous system may rather activate groups of functionally related muscles, known as muscle synergies. To understand how locomotor control adjusts to simulated hypogravity, we examined the temporal (motor primitives) and spatial (motor modules) components of muscle synergies in participants running sequentially at 100%, 60%, and 100% body weight on a treadmill. Our results highlighted the paradoxical nature of simulated hypogravity running: The reduced mechanical constraints allowed for a more flexible locomotor control, which correlated with the degree of spatiotemporal adjustments. Yet, the increased temporal (shortened stance phase) and sensory (deteriorated proprioceptive feedback) constraints required wider motor primitives and a higher contribution of the hamstring muscles during the stance phase. These results are a first step towards improving astronaut training protocols.

Influence of Reduced-Gravity Treadmill Running on Sensor-Derived Biomechanics

BACKGROUND

Reduced gravity treadmills have become increasingly prevalent in clinical settings. The purpose of this study was to assess the influence of manipulated levels of bodyweight during reduced gravity treadmill running on sensor-derived spatiotemporal, kinematic, and kinetic measures.

HYPOTHESES

Reduced gravity conditions would result in significantly altered biomechanical measures compared with 100% gravity conditions, with the most pronounced effects anticipated in the 20% condition.

STUDY DESIGN

Cross-sectional clinic-based study.

METHODS

A total of 16 runners (8 male [M; age, 28.88 ± 5.69 years; body mass index [BMI], 25.08 ± 3.74 kg/m2], 8 female [F; age, 28.75 ± 5.23 years, BMI, 21.05 ± 3.46 kg/m2]) participated in this study. Participants wore commercially available sensors on their shoelaces and ran in a reduced gravity treadmill at a self-selected pace for 5 minutes each at 100%, 80%, 60%, 40%, and 20% bodyweight in a randomized order. The pace remained constant across all conditions, and rating of perceived exertion (RPE) was obtained following each condition. Step-by-step spatiotemporal, kinematic, and kinetic metrics were extracted to calculate mean outcome measures for each bodyweight condition. Repeated measures analyses of variance were conducted to assess the influence of the different bodyweight reduction levels on RPE and runners' biomechanics.

RESULTS

Higher pressure creating lower bodyweight conditions resulted in significantly increased stride length and decreased cadence, contact time, impact g, and RPE, along with a shift toward forefoot strike types compared with higher body weight conditions (P < 0.01). All other outcomes were comparable across conditions.

CONCLUSION

Reduced bodyweight running significantly altered spatiotemporal measures and reduced the vertical component of loading.

CLINICAL RELEVANCE

Our findings offer objective information on expected biomechanical changes across pressure levels that clinicians should consider when incorporating reduced gravity treadmill running into rehabilitation plans.

How about running on Mars? Influence of sensorimotor coherence on running and spatial perception in simulated reduced gravity

Motor control, including locomotion, strongly depends on the gravitational field. Recent developments such as lower-body positive pressure treadmills (LBPPT) have enabled studies on Earth about the effects of reduced body weight (BW) on walking and running, up to 60% BW. The present experiment was set up to further investigate adaptations to a more naturalistic simulated hypogravity, mimicking a Martian environment with additional visual information during running sessions on LBPPT. Twenty-nine participants performed three sessions of four successive five-min runs at preferred speed, alternating Earth- or simulated Mars-like gravity (100% vs. 38% BW). They were displayed visual scenes using a virtual reality headset to assess the effects of coherent visual flow while running. Running performance was characterized by normal ground reaction force and pelvic accelerations. The perceived upright and vection (visually-induced self-motion sensation)in dynamic visual environments were also investigated at the end of the different sessions. We found that BW reduction induced biomechanical adaptations independently of the visual context. Active peak force and stance time decreased, while flight time increased. Strong inter-individual differences in braking and push-off times appeared at 38% BW, which were not systematically observed in our previous studies at 80% and 60% BW. Additionally, the importance given to dynamic visual cues in the perceived upright diminished at 38% BW, suggesting an increased reliance on the egocentric body axis as a reference for verticality when the visual context is fully coherent with the previous locomotor activity. Also, while vection was found to decrease in case of a coherent visuomotor coupling at 100% BW (i.e., post-exposure influence), it remained unaffected by the visual context at 38% BW. Overall, our findings suggested that locomotor and perceptual adaptations were not similarly impacted, depending on the -simulated- gravity condition and visual context.

Neuromuscular adjustments to unweighted running: the increase in hamstring activity is sensitive to trait anxiety

Introduction: Originally developed for astronauts, lower body positive pressure treadmills (LBPPTs) are increasingly being used in sports and clinical settings because they allow for unweighted running. However, the neuromuscular adjustments to unweighted running remain understudied. They would be limited for certain lower limb muscles and interindividually variable. This study investigated whether this might be related to familiarization and/or trait anxiety. Methods: Forty healthy male runners were divided into two equal groups with contrasting levels of trait anxiety (high, ANX⁺, n = 20 vs. low, ANX^-, n = 20). They completed two 9-min runs on a LBPPT. Each included three consecutive 3-min conditions performed at 100%, 60% (unweighted running), and 100% body weight. Normal ground reaction force and electromyographic activity of 11 ipsilateral lower limb muscles were analyzed for the last 30 s of each condition in both runs. Results: Unweighted running showed muscle- and stretch-shortening cycle phase-dependent neuromuscular adjustments that were repeatable across both runs. Importantly, hamstring (BF, biceps femoris; STSM, semitendinosus/semimembranosus) muscle activity increased during the braking (BF: +44 ± 18%, p < 0.001) and push-off (BF: +49 ± 12% and STSM: +123 ± 14%, p < 0.001 for both) phases, and even more so for ANX⁺ than for ANX^-. During the braking phase, only ANX⁺ showed significant increases in BF (+41 ± 15%, p < 0.001) and STSM (+53 ± 27%, p < 0.001) activities. During the push-off phase, ANX⁺ showed a more than twofold increase in STSM activity compared to ANX^- (+119 ± 10% vs. +48 ± 27, p < 0.001 for both). Conclusion: The increase in hamstring activity during the braking and push-off phases may have accelerated the subsequent swing of the free-leg, likely counteracting the unweighting-induced slowing of stride frequency. This was even more pronounced in ANX⁺ than in ANX^-, in an increased attempt not to deviate from their preferred running pattern. These results highlight the importance of individualizing LBPPT training and rehabilitation protocols, with particular attention to individuals with weak or injured hamstrings.

Bodyweight support alters the relationship between preferred walking speed and cost of transport

Humans tend to select a preferred walking speed (PWS) that minimizes the metabolic energy consumed per distance traveled, i.e. the Cost of Transport (CoT). The aims of this study were to: 1. compare PWS overground vs. on a treadmill at 100 and 50% of body weight, and 2. explore whether with body weight support, PWS corresponds to the speed that minimizes CoT. Fifteen healthy adults walked overground and on a lower body positive pressure treadmill with and without bodyweight support. Walking speeds (m^.s^-1) were recorded for each condition. Rate of energy expenditure (J^.kg^-1.min^-1) and CoT (J^.kg^-1.m^-1) were then determined from 5-min walking trials with 50% bodyweight support at PWS and ± 30% of the self-selected walking speed for that condition. PWS did not differ across conditions. With 50% body weight support, for each 30% increase in walking speed, rates of metabolic energy expenditure increased ∼15% while CoT decreased by ∼14%. Thus, with 50% body weight support, PWS did not correspond with the speed that minimized CoT. Bodyweight support decreases cost of maintaining an upright body but does not decrease the metabolic demand of limb advancement, contributing to the linear yet not proportional changes in rates of energy expenditure and CoT. We conclude that bodyweight support via an AlterG® treadmill disconnects the association between PWS and minimum CoT. These findings have implications for clinical populations (e.g., obese, elderly) who may benefit from walking on a bodyweight supporting treadmill but may select speeds incompatible with their physical activity goals.

Influence of exercise intensity and hypoxic exposure on physiological, perceptual and biomechanical responses to treadmill running

AbstractAcute physiological, perceptual and biomechanical consequences of manipulating both exercise intensity and hypoxic exposure during treadmill running were determined. On separate days, eleven trained individuals ran for 45 s (separated by 135 s of rest) on an instrumented treadmill at seven running speeds (8, 10, 12, 14, 16, 18 and 20 km.h^-1) in normoxia (NM, FiO₂ = 20.9%), moderate hypoxia (MH, FiO₂ = 16.1%), high hypoxia (HH, FiO₂ = 14.1%) and severe hypoxia (SH, FiO₂ = 13.0%). Running mechanics were collected over 20 consecutive steps (i.e., after running ∼25 s), with concurrent assessment of physiological (heart rate and arterial oxygen saturation) and perceptual (overall perceived discomfort, difficulty breathing and leg discomfort) responses. Two-way repeated-measures ANOVA (seven speeds × four conditions) were used. There was a speed × condition interaction for heart rate (p = 0.045, ηp²=0.22), with lower values in NM, MH and HH compared to SH at 8 km.h^-1 (125 ± 12, 125 ± 11, 128 ± 12 vs 132 ± 10 b.min^-1). Overall perceived discomfort (8 and 16 km.h^-1; p = 0.019 and p = 0.007, ηp² =0.21, respectively) and perceived difficulty breathing (all speeds; p = 0.023, ηp² =0.37) were greater in SH compared to MH, whereas leg discomfort was not influenced by hypoxic exposure. Minimal difference was observed in the twelve kinetics/kinematics variables with hypoxia (p > 0.122; η_p²= 0.19). Running at slower speeds in combination with severe hypoxia elevates physiological and perceptual responses without a corresponding increase in ground reaction forces.

Role of Antigravity Training in Rehabilitation and Return to Sport After Running Injuries

Anti-gravity treadmill training is a therapeutic option to help recovering runners return to activity after injury. This current concept paper provides a synopsis of the latest evidence of the biomechanical and metabolic changes that occur with body weight support (BWS) treadmill training, effects of antigravity treadmill training on clinical outcomes and clinical case studies in injured runners. Literature searches identified studies with descriptive, experimental and interventional designs and case studies that examined acute and chronic use of antigravity treadmills in runners and relevant populations. Laboratory-based studies were included to provide technical considerations for rehabilitation programming. Antigravity treadmills use causes reductions in cadence, ground reaction forces (GRF), GRF impulses, knee and ankle range of motion, and vertical stiffness, with elevations in stride duration, flight time, ground contact time, and plantarflexion. Antigravity treadmills appear useful across a spectrum of injuries in runners, including postsurgical repair of osteochondral defect, stress reactions (medial tibia, pelvis), and lumbar disc herniation. Runners may preserve aerobic fitness, muscle activation patterns, and muscle mass during recovery compared to traditional rehabilitation protocols. Technical considerations for accurate loading include treadmill frame adjustment to appropriate height to ensure accuracy of level of BWS while running, and monitoring for fast cadence to ensure impact loading rates remain low. Speed or grade can be increased to maintain metabolic demand and fitness while minimizing bone and tissue loading. Monitoring for symptom provocation will guide protocol adjustments to BWS and prescriptions. Once able to run pain-free (sustained or interval) >95% BWS for >30 min, the runner is likely ready to safely transition to ground running. Antigravity treadmill training can be considered when available to facilitate smooth transition back to ground running in a conditioned state.

Gastrocnemius medialis contractile behavior during running differs between simulated Lunar and Martian gravities

The international partnership of space agencies has agreed to proceed forward to the Moon sustainably. Activities on the Lunar surface (0.16 g) will allow crewmembers to advance the exploration skills needed when expanding human presence to Mars (0.38 g). Whilst data from actual hypogravity activities are limited to the Apollo missions, simulation studies have indicated that ground reaction forces, mechanical work, muscle activation, and joint angles decrease with declining gravity level. However, these alterations in locomotion biomechanics do not necessarily scale to the gravity level, the reduction in gastrocnemius medialis activation even appears to level off around 0.2 g, while muscle activation pattern remains similar. Thus, it is difficult to predict whether gastrocnemius medialis contractile behavior during running on Moon will basically be the same as on Mars. Therefore, this study investigated lower limb joint kinematics and gastrocnemius medialis behavior during running at 1 g, simulated Martian gravity, and simulated Lunar gravity on the vertical treadmill facility. The results indicate that hypogravity-induced alterations in joint kinematics and contractile behavior still persist between simulated running on the Moon and Mars. This contrasts with the concept of a ceiling effect and should be carefully considered when evaluating exercise prescriptions and the transferability of locomotion practiced in Lunar gravity to Martian gravity.

AlterG Anti-Gravity Treadmill Accuracy of Unloading Is Affected by Support Frame Height

ABSTRACT

de Heer, HD, Kaufman, A, Repka, CP, Rojas, K, Charley, B, and Bounds, R. AlterG Anti-Gravity Treadmill accuracy of unloading is affected by support frame height. J Strength Cond Res 35(10): 2910-2914, 2021-The AlterG Anti-Gravity Treadmill uses air pressure to provide partial body-weight support (BWS), lowering impact forces and metabolic demand of walking and running. Users wear specialized shorts that zip onto a bag supported by a metal bar frame covering the treadmill. The frame is placed at hip height in positions numbered 1-9, adjusted up or down based on preference. Machine accuracy in providing BWS is important to achieve desired training effects, but it is unknown whether frame placement impacts accuracy. Twenty subjects (10 men/women) were weighed in 10% increments from 0 to 60% BWS with the frame at hip height (iliac crest), the "neutral" position, and reweighed with the frame placed up to 3 numbers above or below hip height. Although the machine displayed the same proportion BWS, placing the frame higher than the neutral position resulted in significantly more support, whereas placing the frame lower led to less support. At 10% BWS, placing the frame 3 positions higher resulted in 3% more support compared with the neutral position (13.1% BWS, p < 0.001) and 3 positions lower in 4.7% less support (5.3% BWS, p < 0.001). Deviances were greater with more BWS. At 60% BWS, 3 positions higher than neutral resulted in 71.2% BWS (11.2% more than expected, p < 0.001) and 3 below 48.1% BWS (12.9% below expected, p < 0.001), total 24.1% difference. These findings suggest that the position of the support frame significantly impacts the AlterG accuracy in providing BWS, with placement higher than hip height resulting in more support than displayed by the machine and lower placement resulting in less support.

Comprehensive Return to Competitive Distance Running: A Clinical Commentary

Running injuries are very common, and there are well-established protocols for clinicians to manage specific musculoskeletal conditions in runners. However, competitive and elite runners may experience different injuries than the average recreational runner, due to differences in training load, biomechanics, and running experience. Additionally, injury-specific rehabilitation protocols do not consider the broader goal of return to competitive running, including the unique psychosocial and cardiorespiratory fitness needs of elite athletes. This review aims to suggest a guideline for running-specific progression as part of a comprehensive rehabilitation program for injured competitive runners. Tools to evaluate an athlete's psychosocial preparedness to return to competition are presented. Recommendations are also provided for monitoring cardiorespiratory fitness of injured runners, including the nuances of interpreting these data. Finally, a six-phase training paradigm is proposed to guide clinicians as they help competitive runners transition from the early stages of injury through a full return to competition.

Mechanics, energetics and implementation of grounded running technique: a narrative review

Grounded running predominantly differs from traditional aerial running by having alternating single and double stance with no flight phase. Approximately, 16% of runners in an open marathon and 33% of recreational runners in a 5 km running event adopted a grounded running technique. Grounded running typically occurs at a speed range of 2–3 m·s⁻¹, is characterised by a larger duty factor, reduced vertical leg stiffness, lower vertical oscillation of the centre of mass (COM) and greater impact attenuation than aerial running. Grounded running typically induces an acute increase in metabolic cost, likely due to the larger duty factor. The increased duty factor may translate to a more stable locomotion. The reduced vertical oscillation of COM, attenuated impact shock, and potential for improved postural stability may make grounded running a preferred form of physical exercise in people new to running or with low loading capacities (eg, novice overweight/obese, elderly runners, rehabilitating athletes). Grounded running as a less impactful, but metabolically more challenging form, could benefit these runners to optimise their cardio-metabolic health, while at the same time minimise running-related injury risk. This review discusses the mechanical demands and energetics of grounded running along with recommendations and suggestions to implement this technique in practice.

Effect of Uphill Running on VO2, Heart Rate and Lactate Accumulation on Lower Body Positive Pressure Treadmills

Lower body positive pressure treadmills (LBPPTs) as a strategy to reduce musculoskeletal load are becoming more common as part of sports conditioning, although the requisite physiological parameters are unclear. To elucidate their role, ten well-trained runners (30.2 ± 3.4 years; VO_2max: 60.3 ± 4.2 mL kg^-1 min^-1) ran at 70% of their individual velocity at VO_2max (vVO_2max) on a LBPPT at 80% body weight support (80% BW_Set) and 90% body weight support (90% BW_Set), at 0%, 2% and 7% incline. Oxygen consumption (VO₂), heart rate (HR) and blood lactate accumulation (LA) were monitored. It was found that an increase in incline led to increased VO₂ values of 6.8 ± 0.8 mL kg^-1 min^-1 (0% vs. 7%, p < 0.001) and 5.4 ± 0.8 mL kg^-1 min^-1 (2% vs. 7%, p < 0.001). Between 80% BW_Set and 90% BW_Set, there were VO₂ differences of 3.3 ± 0.2 mL kg^-1 min^-1 (p < 0.001). HR increased with incline by 12 ± 2 bpm (0% vs. 7%, p < 0.05) and 10 ± 2 bpm (2% vs. 7%, p < 0.05). From 80% BW_Set to 90% BW_Set, HR increases of 6 ± 1 bpm (p < 0.001) were observed. Additionally, LA values showed differences of 0.10 ± 0.02 mmol l^-1 between 80% BW_Set and 90% BW_Set. Those results suggest that on a LBPPT, a 2% incline (at 70% vVO_2max) is not yet sufficient to produce significant physiological changes in VO₂, HR and LA-as opposed to running on conventional treadmills, where significant changes are measured. However, a 7% incline increases VO₂ and HR significantly. Bringing together physiological and biomechanical factors from previous studies into this practical context, it appears that a 7% incline (at 80% BW_Set) may be used to keep VO₂ and HR load unchanged as compared to unsupported running, while biomechanical stress is substantially reduced.

Effect of speed and gradient on plantar force when running on an AlterG® treadmill

BACKGROUND

Anti-gravity treadmills are used to decrease musculoskeletal loading during treadmill running often in return to play rehabilitation programs. The effect different gradients (uphill/downhill running) have on kinetics and spatiotemporal parameters when using an AlterG® treadmill is unclear with previous research focused on level running only.

METHODS

Ten well-trained healthy male running athletes ran on the AlterG® treadmill at varying combinations of bodyweight support (60, 80, and 100% BW), speed (12 km/hr., 15 km/hr., 18 km/hr., 21 km/hr., and 24 km/hr), and gradients (- 15% decline, - 10, - 5, 0, + 5, + 10 + 15% incline), representing a total of 78 conditions performed in random order. Maximum plantar force and contact time were recorded using a wireless in-shoe force sensor insole system.

RESULTS

Regression analysis showed a linear relationship for maximum plantar force with bodyweight support and running speeds for level running (p < 0.0001, adj. R² = 0.604). The linear relationship, however, does not hold for negative gradients at speeds 12 & 15 km/h, with a relative 'dip' in maximum plantar force across all assisted bodyweight settings.

CONCLUSIONS

Maximum plantar force peaks are larger with faster running and smaller with more AlterG® assisted bodyweight support (athlete unweighing). Gradient made little difference except for a downhill grade of - 5% decreasing force peaks as compared to level or uphill running.

Making the Grade: An Exploration of Incline Running on a Bodyweight-Supportive Treadmill

CONTEXT

Bodyweight-supporting treadmills are popular rehabilitation tools for athletes recovering from impact-related injuries because they reduce ground reaction forces during running. However, the overall metabolic demand of a given running speed is also reduced, meaning athletes who return to competition after using such a device in rehabilitation may not be as fit as they had been prior to their injury.

OBJECTIVE

To explore the metabolic effects of adding incline during bodyweight-supported treadmill running.

DESIGN

Cross-sectional.

SETTING

Research laboratory.

PARTICIPANTS

Fourteen apparently healthy, recreational runners (6 females and 8 males; 21 [3] y, 1.71 [0.08] m, 63.11 [6.86] kg).

INTERVENTIONS

The participants performed steady-state running trials on a bodyweight-supporting treadmill at 8.5 mph. The control condition was no incline and no bodyweight support. All experimental conditions were at 30% bodyweight support. The participants began the sequence of experimental conditions at 0% incline; this increased to 1%, and from there on, 2% incline increases were introduced until a 15% grade was reached. Repeated-measures analysis of variance was used to compare all bodyweight-support conditions against the control condition.

MAIN OUTCOME MEASURES

Oxygen consumption, heart rate, and rating of perceived exertion.

RESULTS

Level running with 30% bodyweight support reduced oxygen consumption by 21.6% (P < .001) and heart rate by 12.0% (P < .001) compared with the control. Each 2% increase in incline with bodyweight support increased oxygen consumption by 6.4% and heart rate by 3.2% on average. A 7% incline elicited similar physiological measures as the unsupported, level condition. However, the perceived intensity of this incline with bodyweight support was greater than the unsupported condition (P < .001).

CONCLUSIONS

Athletes can maintain training intensity while running on a bodyweight-supporting treadmill by introducing incline. Rehabilitation programs should rely on quantitative rather than qualitative data to drive exercise prescription in this modality.

Cardiorespiratory and metabolic responses to exercise testing during lower-body positive pressure running

Exercise reduces the future cardiometabolic disease risk. However, not everyone can participate in routine physical activity because of obesity or orthopedic impairments. Body weight-supported (BWS) exercise may be an option for these individuals. Unfortunately, very little data are available with regard to BWS running in untrained healthy individuals. Yet, this information is important to assess the potential use of lower-body positive pressure (LBPP) treadmill running for the prevention of cardiometabolic disease. Twenty healthy but untrained participants (10 females, mean age 31.5 yr) were included in this study. Participants completed two exercise tests (one with 100% and one with 60% body wt) in randomized order on a LBPP treadmill. Expired gas data and heart rate (HR) were collected continuously. Blood lactate, blood pressure (BP), pulse wave velocity (PWV), and rating of perceived exertion (RPE) were measured during a 2-min break after each stage. Oxygen uptake increased significantly independent of BWS but was lower with BWS. Furthermore, we identified a significant correlation between HR and RPE independent of BWS. BP and PWV showed a large heterogeneity in response to BWS. The lower O₂ requirement when running with BWS may help untrained individuals to adapt to an exercise regimen. Future research needs to explore the heterogenetic response of blood pressure and pulse wave velocity to LBPP BWS between individuals.NEW & NOTEWORTHY Lower-body positive pressure body weight-supported exercise has a lower metabolic and cardiovascular demand. Furthermore, heart rate and rating of perceived exertion are highly correlated independent of body weight support. Our data support the further examination of lower-body positive pressure exercise training for cardiovascular disease risk groups.

Walking on the Moon: A randomized clinical trial on the role of lower body positive pressure treadmill training in post-stroke gait impairment

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The effects of LBPP on locomotion in neurologic patients are poorly predictable.

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The mechanisms through which LPBB acts on gait are partially unknown.

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Gait training using AlterG improves functional gait in post-stroke patients.

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AlterG increases muscle activation and/or phasic muscle activation in post-stroke.

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This knowledge may be useful to plan patient-tailored LBPP locomotor training.

Body weight–supported treadmill training (BWSTT) can be usefully employed to facilitate gait recovery in patients with neurological injuries. Specifically, lower body positive pressure support system (LBPPSS) decreases weight-bearing and ground reaction forces with potentially positive effects on qualitative gait indices. However, which gait features are being shaped by LBPPSS in post-stroke patients is yet poorly predictable. A pilot study on the effects of LBPPSS on qualitative and quantitative gait indices was carried out in patients with hemiparesis due to stroke in the chronic phase. Fifty patients, who suffered from a first, single, ischemic, supra-tentorial stroke that occurred at least 6 months before study inclusion, were enrolled in the study. They were provided with 24 daily sessions of gait training using either the AlterG device or conventional treadmill gait training (TGT). These patients were compared with 25 age-matched healthy controls (HC), who were provided with the same amount of AlterG. Qualitative and quantitative gait features, including Functional Ambulation Categories, gait cycle features, and muscle activation patterns were analyzed before and after the training. It was found that AlterG provided the patients with higher quantitative but not qualitative gait features, as compared to TGT. In particular, AlterG specifically shaped muscle activation phases and gait cycle features in patients, whereas it increased only overall muscle activation in HC. These data suggest that treadmill gait training equipped with LBPPSS specifically targets the gait features that are abnormal in chronic post-stroke patients. It is hypothesizable that the specificity of AlterG effects may depend on a selective reshape of gait rhythmogenesis elaborated by the locomotor spinal circuits receiving a deteriorated corticospinal drive. Even though further studies are warranted to clarify the role of treadmills equipped with LBPPSS in gait training of chronic post-stroke patients, the knowledge of the exact gait pattern during weight-relief is potentially useful to plan patient-tailored locomotor training.

Effect of body weight support on muscle activation during walking on a lower body positive pressure treadmill

Following lower limb injury, some patients are not able to walk at full weight bearing and may require body weight support for ambulation during the early stages of rehabilitation. The aim of the present study was to investigate how various degrees of reduced effective body weight in a Lower Body Positive Pressure Treadmill (LBPPT), affects muscle activation levels during walking. Twelve healthy participants were instructed to walk at 2.5 km/h and 3.6 km/h on a LBPPT that provided a reduced effective body weight equivalent to 100%, 80%, 60%, 40%, and 20% of their individual body mass. Electromyography data were recorded during 20 gait cycles, from seven lower limb muscles, and segmented into a mean envelope by computing root mean square values. A two-way repeated measures ANOVA was used to test for differences in the highest root mean square value obtained, with walking speed and fractional reduction in effective body weight as factors. Significant decreases in EMG amplitude were identified in the following muscles as a result of reduced effective body weight: Vastus Medialis, Vastus Lateralis, Soleus, Gastrocnemius Medial and Lateral head (p ≤ 0.05). For Tibialis Anterior, significant reductions in EMG amplitude were only observed when effective body weight was reduced to 40% or less at a walking speed of 2.5 km/h (p ≤ 0.05). The EMG amplitude for Tibialis Anterior at 3.6 km/h and Biceps Femoris at both speeds remained unaffected at all fractional reductions (p ≥ 0.05). These findings suggests that the muscles of the lower limb respond differently to the body weight support provided by the LBPPT during walking, with the extensor muscles of the knee and ankle displaying decreased muscle activation, and the Tibialis Anterior and Biceps Femoris displaying minimal to no changes in muscle activation.

Physiological and Biomechanical Responses of Highly Trained Distance Runners to Lower-Body Positive Pressure Treadmill Running

Background

As a way to train at faster running speeds, add training volume, prevent injury, or rehabilitate after an injury, lower-body positive pressure treadmills (LBPPT) have become increasingly commonplace among athletes. However, there are conflicting evidence and a paucity of data describing the physiological and biomechanical responses to LBPPT running in highly trained or elite caliber runners at the running speeds they habitually train at, which are considerably faster than those of recreational runners. Furthermore, data is lacking regarding female runners’ responses to LBPPT running. Therefore, this study was designed to evaluate the physiological and biomechanical responses to LBPPT running in highly trained male and female distance runners.

Methods

Fifteen highly trained distance runners (seven male; eight female) completed a single running test composed of 4 × 9-min interval series at fixed percentages of body weight ranging from 0 to 30% body weight support (BWS) in 10% increments on LBPPT. The first interval was always conducted at 0% BWS; thereafter, intervals at 10, 20, and 30% BWS were conducted in random order. Each interval consisted of three stages of 3 min each, at velocities of 14.5, 16.1, and 17.7 km·h⁻¹ for men and 12.9, 14.5, and 16.1 km·h⁻¹ for women. Expired gases, ventilation, breathing frequency, heart rate (HR), rating of perceived exertion (RPE), and stride characteristics were measured during each running speed and BWS.

Results

Male and female runners had similar physiological and biomechanical responses to running on LBPPT. Increasing BWS increased stride length (p < 0.02) and flight duration (p < 0.01) and decreased stride rate (p < 0.01) and contact time (p < 0.01) in small-large magnitudes. There was a large attenuation of oxygen consumption (VO₂) relative to BWS (p < 0.001), while there were trivial-moderate reductions in respiratory exchange ratio, minute ventilation, and respiratory frequency (p > 0.05), and small-large effects on HR and RPE (p < 0.01). There were trivial-small differences in V_E, respiratory frequency, HR, and RPE for a given VO₂ across various BWS (p > 0.05).

Conclusions

The results indicate the male and female distance runners have similar physiological and biomechanical responses to LBPPT running. Overall, the biomechanical changes during LBPPT running all contributed to less metabolic cost and corresponding physiological changes.