A 21-year-old male (168 cm, 47.8 kg) with spinal muscular atrophy type III when diagnosed at 18-years old by genetic screening participated in this study. Written informed consent was obtained from the patient to perform the two types of gait training and to publish the obtained his anonymized data to be published in this article. All procedures were performed in accordance with the Declaration of Helsinki and were approved by the Hiroshima University's Committee on Ethics in Research (approval Number No. E-53). He presented with forearm distal muscle weakness, atrophy of the intrinsic muscles of the hand, and neuromuscular fatigue. The patient's baseline physical performance data are shown in Table 1. The age-matched normative values for knee extension strength and six minutes walking test (6MWT) are 2.82+-0.38 Nm/kg and 637 m.  ,   The participants' knee extension strength (Right: 1.59 Nm/kg, Left; 1.32 Nm/kg) and 6MWT (567 m) were lower than the above value, and we have chosen the weaker leg to measure EMS recording.  
The participant performed maximal isometric voluntary contractions (MVC) of the knee extensors bilaterally at the pre- and post-intervention. Isometric knee extension was performed using a Biodex system (Biodex System 4; Biodex Medical Systems, Shirley, NY, USA). During contractions, both the hip and knee extension angles were positioned at 90 degrees. The MVC involved a gradual increase in knee extension torque from 0 Nm to his maximum torque over three seconds, with the maximum torque being held for two seconds. The participant performed at least two MVC trials with > 120 s of rest between trials and a warm-up for 10 min, including indoor walking and lower limb stretching before the MVC measurement.    The peak MVC torque was used as the maximal effort and to calculate the target torque for the isometric sub-maximal ramp-up contractions. After MVC measurements, the participant performed an isometric submaximal ramp-up contraction of the knee extensors in the weaker leg one time from 0% to 80% of the MVC force with an increase rate of approximately 10% of the MVC per sec.  ,   The participant-generated torque and target torque were displayed on a computer monitor. Prior to motor testing, the participant practiced the MVC and sub-maximal ramp-up contraction at least 10 min before the motor testing session began. The CoV of force (standard deviation (SD)/mean x 100, CV force) was calculated from the ramp up contraction task.
During the sub-maximal contraction, multi-channel SEMG signals were detected from the weaker side of vastus lateralis (VL) muscle using a semi-disposable grid of 64 electrodes (ELSCH064NM2; OTBioelettronica, Torino, Italy) according to the same procedures used in previous studies.  , , ,   The grid consisted of 13 columns and five rows of electrodes (diameter, 1mm; inter-electrode distance, 8mm in each direction), with one missing electrode in the upper left corner. The participant's thigh hair was removed, and the skin was cleaned with alcohol. The electrode was attached to the skin with a bi-adhesive sheet (KITAD064NM2; OTBioelettronica) after a conductive paste (Elefix Z-181BE; NIHON KOHDEN, Tokyo, Japan) was applied. The center of the electrode grid was positioned at the center of the line between the superior lateral edge of the patella and the greater trochanter protuberance. The columns of the electrode grid were placed parallel to the longitudinal axis of the VL muscle. A reference electrode was attached at the anterior superior iliac spine.  , , ,   All procedures were performed by the same investigator.
Monopolar multi-channel surface EMG signals (64 channels) were amplified by a factor of 1000, sampled at 2048 Hz, and digitized by a 12-bit analog-to-digital converter (EMG-USB2+, OTBioelettronica). The recorded monopolar signals were off-line bandpass filtered (10-500 Hz) and transferred to analysis software (MTALAB 2019a, MathWorks GK, MA, USA). Bipolar multi-channel SEMG signals (n = 59) along the columns were obtained from the 64 electrodes. The EMG signals were divided in epochs of one second centered at each 10% of MVC force increment from 10% to 80% of the MVC ramp-contraction to calculate the root mean square (RMS).    Since the selected ramp rate was 10% of the MVC force per second, one epoch of the sampled signal was overlapped by 0.5 seconds between neighboring torque levels. We normalized the RMS estimates to the values obtained pre-intervention for each torque level.
To characterize the heterogeneity in the multi-channel SEMG spatial distribution pattern at each epoch, we determined the modified entropy and correlation coefficients. The modified entropy of the spatial distribution of the DeltaSEMG amplitude was calculated over a 1-s epoch taken at 10% to 80% of the MVC during the ramp-up contraction. According to methods published by Farina et al., modified entropy was defined as the entropy of the signal power as follows:     
where p( i) is the square of the RMS value of channel i divided by the sum of the squares of all 59 RMS values at the given contraction level. Therefore, p( i) 2 represents the normalized power of each channel. Modified entropy is the normalized power of the EMG signal across the array and reflects the heterogeneity in the muscle activity. The CoV of the RMS was defined as the quotient of the SD of the Delta59 RMS measurements and the average of Delta59 RMS measurements at each given torque level.    Both a decrease in modified entropy and an increase in CoV of RMS indicate increased heterogeneity in the multi-channel SEMG spatial distribution pattern within the electrode grid.  ,   Measures of the CoV of the RMS and modified entropy provide insight into how the nervous system regulates muscle activation across the muscle irrespective of the magnitude.    
The patient performed two types of gait training separated by a period of one month between training to avoid training effect.
  HAL gait training  
The patient performed gait training using the HAL for 33 minutes (gait distance about 2200 m). The double leg type HAL was used for gait training, which was performed with two physical therapists for the operation of the HAL commands and support of the patient. During HAL gait training, a walking hoist (ALL IN ONE walking hoist, ROPOX, Denmark) was used to prevent falls and adjust the patient's posture.
  Treadmill gait training  
The patient performed gait training using the treadmill for 33 minutes (gait speed 4.0 km/h, gait distance about 2200 m). During gait training, Alter-G (Alter-G, Inc., Fremont, CA, USA) was used to prevent falls and adjust the patient's posture without providing weight bearing and clinician's support to leg movements.