# Adaptation in Gait to Body-Weight Unloading
## 4 Discussion
### Emg
#### 4.4.2 Post-Adaptation  
Neuromuscular changes after unloading were most evident in RF and TA muscles. Additionally, these changes occurred close to two discrete events in the gait cycle which are characterized by large amounts of energy transfers, namely the heel strike and toe off. These observations are similar to those reported in spaceflight-related locomotor studies pointing towards some potentially common adaptive mechanisms [20; 33; 42]. As in the case with kinematics, there were no significant changes in neuromuscular activity of any of the muscles either during or after the control adaptation session. This further reiterates that the observed changes in neuromuscular activities after unloading are not caused due to fatigue but rather due to adaptation to unloaded walking. Although statistically insignificant, some visually evident changes in activity of some muscles were observed during certain phases of the gait cycle in the control condition. We speculate that these changes are mere random fluctuations as there are no specific methodological or physiological reasons as to why such changes might occur. Around heel strike, we saw an increase in RF activity during the loading phase immediately after unloaded walking, combined with a reduction in knee and ankle angular excursion. This could be in response to the large ground reaction forces that the body encountered during the loading phase relative to that encountered during unloaded walking. [PERSON] et al. [20] also found an increase in RF activity during the stance phase of the gait cycle after long-duration spaceflight. It has been suggested that modifications in RF activity combined with increased kinematic variability after spaceflight are attempts to attenuate the energy generated by the ground reaction forces around heel strike that are transmitted to the head [42; 48; 50; 51]. Apart from heel-strike-specific modulations, we also observed a small reduction in RF and BF activity during the mid-stance and terminal stance phases of the gait cycle during some of the epochs. Although RF and BF have limited functional roles during these phases, these changes reflect an overall reinterpretation of sensory inputs as a result of adaptation to unloading. Around toe off, there was a significant reduction in RF activity during the pre-swing phase after the first 100 strides (T\({}_{2}\)) post-unloading adaptation session. As mentioned earlier, the RF activity during the pre-swing phase is responsible for lifting the leg so that it can be propelled forward during the swing phase. During unloading, as expected, we saw a reduction in activity during this phase as the muscular effort required to propel the leg is less. Extending this logic, we would expect the muscular effort post-unloading to increase due to the increase in body-weight load. As expected, the RF activity increased at T\({}_{1}\) relative to T\({}_{\text{during}}\). This increase in RF activity was however transient, as it was significantly reduced from T\({}_{2}\) up to 10 min. A reduction in RF activity was also combined with reduced angular excursion of ankle and knee joints during some epochs. With regards to TA, we observed an increase in activity during the mid-swing phase. This must have been an attempt by the motor control system to compensate for reduced knee flexion by increasing its activity to increase the dorsiflexion about the ankle joint for adequate clearance of the toe. Since we did not observe any foot-scraping events in any of the subjects, it seems that the ankle dorsiflexion during the mid-swing phase was sufficient for toe clearance. The above patterns of reduced RF activity during the pre-swing phase and increased TA activity during the mid-swing phase of the gait cycle were also observed after long-duration spaceflight during treadmill walking [20]. The fact that a short exposure of 30 min of body-weight unloading on Earth resulted in similar patterns of neuromuscular changes as those observed after long-duration spaceflightis interesting.