Muscle Activation and Estimated Relative Joint Force During Running with Weight Support on a Lower-Body Positive-Pressure Treadmill

Abstract

Running on a lower-body positive-pressure (LBPP) treadmill allows effects of weight support on leg muscle activation to be assessed systematically, and has the potential to facilitate rehabilitation and prevent overloading. The aim was to study the effect of running with weight support on leg muscle activation and to estimate relative knee and ankle joint forces. Runners performed 6-min running sessions at 2.22 m/s and 3.33 m/s, at 100%, 80%, 60%, 40%, and 20% body weight (BW). Surface electromyography, ground reaction force, and running characteristics were measured. Relative knee and ankle joint forces were estimated. Leg muscles responded differently to unweighting during running, reflecting different relative contribution to propulsion and antigravity forces. At 20% BW, knee extensor EMG peak decreased to 22% at 2.22 m/s and 28% at 3.33 m/s of 100% BW values. Plantar flexors decreased to 52% and 58% at 20% BW, while activity of biceps femoris muscle remained unchanged. Unweighting with LBPP reduced estimated joint force significantly although less than proportional to the degree of weight support (ankle). It was concluded that leg muscle activation adapted to the new biomechanical environment, and the effect of unweighting on estimated knee force was more pronounced than on ankle force. Keywords: rehabilitation, body weight support, EMG, estimated joint load, runningEarly mobilization after injury and surgery on the lower extremities is essential to reduce adverse effects of immobilization and to facilitate rehabilitation. Walking or running with weight support on a lower-body positive-pressure (LBPP) treadmill is a new training and rehabilitation modality. 1,2 A recent study indicated strong correlation between tibiofemoral force and treadmill ground reaction force in a small group of elderly patients during slow walking. 3 Another study showed that runners can reduce peak vertical ground reaction forces while maintaining the aerobic stimulus when running on a LBPP treadmill. 4 Even training at high speeds and high aerobic stimuli with the benefit of low vertical ground reaction force and near-normal movement pattern can be performed on the LBPP treadmill. 5 Furthermore, no adverse impact on systemic and head cardiovascular parameters has been found. 6 However, the effect of different levels of LBPP weight support during running on neuromuscular adaptations and their possible associations to joint forces have not been studied systematically.During level running, leg muscles support body weight (BW) against gravity and accelerate/decelerate the body mass in a forward direction. BW, as measured in Newton, is directly related to gravity, while body mass (kg) is independent of gravity. Therefore, by unweighting in a LBPP chamber, it is possible to create a new biomechanical environment where the vertical forces are reduced while forces associated with horizontal acceleration/deceleration of the body remain unchanged. This allows systematic study of individual leg muscle contribution to body support against grav...

Mars walking simulation: An electromyographic analysis

“…Our findings also contrast with the few running studies conducted in this area 10,11,12,13,14,15 . A noteworthy finding of Hunter (2014) 10 was that hip adductor activity during the swing phase and medial and lateral hamstring activity during the first half of the stance phase were relatively unaltered with various levels of bodyweight support.…”

“…A noteworthy finding of Hunter (2014) 10 was that hip adductor activity during the swing phase and medial and lateral hamstring activity during the first half of the stance phase were relatively unaltered with various levels of bodyweight support. This finding for the hamstrings has been substantiated elsewhere in the literature in the biceps femoris 12,13 . While this may be perceived as somewhat supporting our findings, since these muscles are also instrumental in locomotion, Hunter (2014) 10 postulated that this was perhaps due to participants being unaccustomed to ambulation with LBPP and that with more familiarisation and training, a significant effect may have been observed.…”

“…Using this technology mostly to assess its efficacy as a gait rehabilitation tool, a handful of studies have employed EMG in lower body musculature 10,11,12,13,14,15 . All of these studies reported reductions in levels of muscle activity with bodyweight support.…”

Kinetics and Muscle Activity Patterns during Unweighting and Reloading Transition Phases in Running

“…However, the distinction of the stance and flight phases revealed inter-muscular differences in the unweighting-induced EMG decrease, with no significant change in the hamstring activation during the stance phase [12]. Similarly Jensen et al [13] reported unchanged hamstring activation and larger decreases in the vasti than in the triceps surae muscle activation. The additional distinction of the preactivation, braking and push-off phases revealed an unchanged preactivation of the triceps surae muscle group followed by a large decrease, but during the push-off phase only [14].…”

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

“…This finding is suggestive of a correlation between AlterG-induced symmetric improvement of temporal variables of gait and the specific, more symmetric, support to the stance phase and swing initiation by part of LBPP. In particular, AlterG shaped RF and G muscles, which are central to opposing to gravity force [52]. Having bilaterally rebalanced the activation of G may have been important in gait improvement given that G acts as either a propulsive muscle during walking (by providing hip extension during the stance phase) or a muscle that prevents the foot from hitting the ground (by creating a flexion of the knee during the swing phase) [51].…”