# Rehabilitative Ultrasound Imaging Evaluation in Physiotherapy: Piloting a Systematic Review
## 4 Discussion
### Observational Studies  
The observational studies have allowed us to test the real effects of certain physiotherapeutic interventions and compare them in some cases with other unknown variables, such as the activation of the muscles by using ultrasound. Therefore, the effects of exercises on unstable surfaces, lifting weights, or walking were evaluated in this section.  
The unstable base of support (BOS) exercises, combined with weight-bearing [48], gave better contraction of the lumbar muscles when the exercises were performed in combination than alone on an unstable base; these results were contrary to what was thought at the time. The lumbar stabilization exercises are another frequent approach used in physiotherapy, given that they have shown an improvement in patients with pain assessed by ultrasound [49] in the thickening and activation in relation to the improvement in pain and functionality.  
On some occasions, evaluating the local muscles compared to the regional ones could be of great interest with regard to the common synergies, both in the asymptomatic and symptomatic states. For this evaluation, in a study of patients with sacroiliac joint dysfunction [50], the changes were evaluated, both in the multifidus muscles as well as the abdominal ones. It would have been logical to think there would be a change, but it was demonstrated that it was associated with the sacroiliac joint dysfunction side. Along this line, however, correlations were made between the pain through the visual analogue scale (VAS) and ultrasound, in which the healthy side was compared with the affected side [2]. The linear regression of this comparison showed that the greater the ratio between the healthy and pathological sides, the harsher the symptoms.  
In view of this discovery, we could be led to believe that the review of all the evidence (complete systematic review) could give more consistent results concerning correlations between ultrasound and other variables.  
The lines of research which are beginning to develop are of great interest, in which new variables such as echo intensity and the variety of greys evaluated in the image post-acquisition phase through software are correlated [51]. These findings could then be correlated with variables such as muscle thickness or pain.  
The comparisons between electromyography (EMG) and ultrasound have also been performed and have led to the ultrasound being considered a useful tool for evaluating functionality. Although in some studies, it has been performed on a healthy population [52], a correlation has been found in ultrasound output and EMG results between the increase in external oblique muscle activation and thickening abdominal transverse muscle thickening, and changes in the multifidus muscle that represents progress in monitoring muscle activity.  
The comparison between ultrasound and EMG in muscle activation is worth highlighting [53]. In this study, muscles at rest and at maximum voluntary contraction were assessed in 30 healthy volunteers, yielding a correlation between ultrasound measurements and EMG monitoring of \(r=0.51\)-\(0.61\), which leads to the ultrasound increasingly being considered as a tool for measuring the activity.