The maximum error of different subject in third sub-term. (Standard deviation are 5, 10 and 7.5 for three sub-term respectively) In the third sub-term lumber muscles of some of subject did not follow specific patterns (sign with -).

In Table 1 due to low errors, only maximum errors were listed. The three sub-terms contained the beginning of record until the 90th second, from the 90th second to the 600th second, from the 600th second to the 900th second. The basis vectors investigated in each sub-term separately. 15 minute test time was divided into the three sub-terms according to the results of investigation. The basis vectors in each interval were compared element to element with other intervals and errors were calculated. In each interval, the basis vectors and activation coefficients were estimated using HALS algorithm. Average error of 50,100 and 200 contractions were 5.8 exp -17, 6.1 exp -12 and 2.7 exp -3 respectively, as you see accuracy of 50 and 100 were closed to each other, so we selected 100 contractions as a interval which is Equal 10 seconds because of less computation.) We excuted 50,100 and 200 contractions as one interval respectively. More number of contraction not only have more accuracy but also takes more time, therefore we should consider both of them. In addition, the accuracy of our approach is important. One of purpose of this study was to design spesefic sensor in order to measure level of fatigue in lumber muscle of people, so we need a real time computation. (in the previous works one phase of special movement were selected like grasping but in this study we did not have define interval. In the next step, 10 second intervals in the sEMG signal were selected. Maximum error between reconstruction signals of the original signals in all of subjects is 7.2 exp -10. Illustrates the changes of R 2 against the number of synergies. ( 2) shows changes versus the number of synergies. In this study, four Synergies were selected for leg muscles, because after four synergies R 2 is constant. Where SST is the sum of the squared residuals, and SSE is the sum of the squared residual from the mean activation vector ( ). R 2 represents the fraction of total variation accounted for by the synergy reconstruction. R 2 criteria were used to assess the number synergy. Muscles synergy patterns were extracted from EMG by using Non-Negative Matrix Factorization and HALS algorithm during daily activities. These days, how body of human can organize its muscles to perform certain task like gait, is one of major issues for researchers. So this study only investigated males and tried to reach a clear answer to this question: what is the effect of fatigue on lumber muscles patterns? Females and males move their lumbar spine with different modes for doing the same performance. The difference between the interaction patterns of lumbar muscles in patients and healthy subjects can be used to classify neuromuscular control impairments associated with low back pain. Since the lower back muscles fatigue is associated with sitting mechanism, previous studies investigated the different mechanism of sitting, different kinds of chairs and their relationship to lumbar pain. The suppressive factor of permanent sitting is muscle fatigue and it is possible to determine that by recorded sEMG signals. Despite reduction in median frequency (MDF) change is not observed in sustained contractions this is due to recruitment of additional motor units by lumber muscles to compensate the force loss according to “size principle”. Mechanical movements can be used to reduce fatigue. Many factors of fatigue are effective in the electromyogram signal such as: amplitude and frequency spectrum shift. Females are more resistant to fatigue due to some effective factors including: muscle mass, substrate utilization, muscle morphology, and neuromuscular activation patterns. The main tasks of these muscles are load distribution, load transfer and control of movement. There is a complex network of muscles in the lumbar spine consisting of nearly 70 muscles of variable size. So in this study the best sitting mode is when the lordosis is similar to that of standing position. The best sitting mode is still unclear, but in general lumbar lordosis should be avoided. Suitable neuromuscular control of lumbar spine can prevent spinal disorders. Muscle fatigue is a result of continuous contraction of muscles which leads to a decrease in production or keeping power.

Define synergy pattern