Large scale studies investigating changes in COP excursions associated with manual therapy have been announced at scientific conferences but are yet to be published . COP measures have also been specifically suggested as a monitoring tool for chiropractic practice . This, however, is premature. So far only a few studies have been reported and three of these were under-graduate theses [28–30] that have not been additionally published in a peer reviewed journal to this point.
COP measures are used by some practitioners applying manual therapies, so the lack of good quality studies may suggest that publication bias may play a role. This refers to the tendency on the part of authors to submit, as well as the reviewers and editors to accept, manuscripts based on the study findings  as the strongest and most positive studies are most likely to be published .
Overall, any interpretation of the reported results is severely limited by a lack of detail in the employed study designs that were often not suited to answer the self-defined research question [19, 21, 24, 28, 30]. In addition, the included studies were all found to be either at high or unclear risk of bias.
Important limitations were the absence of a comparison or control/placebo group in all but two studies [23, 29], the generally small samples sizes and the often low or unclear reliability of the obtained sway data. For example, the majority of studies generally employed rather short sampling durations. The test-retest variability in postural sway that may occur as a result can lead to the false impression of changes in the outcome measure post-intervention. Although Vaillant et al.  used six repetitions, the combined sampling duration of 50sec was still fairly short which may have adversely affected the results.
In addition, no sample size calculations were reported to assess when statistical significance may be reached between intervention and control/placebo groups. Where multimodal interventions were used [19–22, 24, 27], the effectiveness of particular treatments remains unclear. In those instances where changes in postural sway were reported [19, 24, 30], it was not possible to determine whether the intervention itself or learning effects due to repetitive testing  may have been causative.
Furthermore, the fact that most studies performed the follow-up measurements immediately after the intervention [19, 23, 28–30], no conclusions can be reached whether any observed changes are sustained. None of the studies using follow-ups of several weeks [20, 21, 24] employed multiple measurements at regular intervals that may have allowed an appreciation of associations between pain and postural sway or learning effects due to repetitive testing.
However, it appears that when healthy participants were tested, generally no significant change in postural sway between COP excursions pre- and post-intervention was noted [19, 23, 30]. When Nolan reported a significant decrease in postural sway associated with cervical SMT  this may be explained by the fact that the Biodex Balance System was the only forceplate used that allowed surface perturbation and a sway degree based COP parameter to be employed.
With regards to the study by Persson et al., there is no conclusive evidence that massage is an effective treatment for cervical nerve root compression . This may at least partly explain why the perceived pain levels did not decrease significantly and, as a correlation between these two factors exists , the COP excursions remained similar to pre-intervention stage.
The results reported by Vaillant et al.  further indicate that the mobilization intervention either had no immediate effect on postural sway with eyes open, or that any such effect remained undetectable when allowing visual fixation. This is supported by the decrease in COP displacement under visual obstruction.
Finally, the results reported by Giemza et al.  warrant some caution. Firstly, the data collected from the thirty healthy controls to be compared to that of the symptomatic patients was not actually reported in the study. Secondly, no symptomatic controls were selected. The 6 weeks interval between the two measurements of questionable reliability does also allow for many factors to influence postural sway, including learning effects. In addition, it was mentioned that the in addition to increasing range of motion, the kinesitherapy also aimed at reducing the "great pain" of the patients. However, no pain levels were recorded pre- and post-intervention that may offer an explanation for changes in postural sway.
Based on the literature available, there is no conclusive evidence that manual therapeutic interventions exhibit any short term effect on body sway, at least in asymptomatic participants, for the COP parameters employed. Other parameters, such as those based on frequency or amplitude, may provide additional insights.
There is weak evidence that a significant decrease in pain perception in symptomatic individuals was associated with decreasing COP excursions [20, 22], while at similar pain perception, postural sway remained unchanged [21, 22]. Accordingly, it appears likely that the pain reduction itself is responsible for the observed lower postural sway in those experiencing pain relief.
The manual intervention itself on the other hand does not appear to offer any additional biomechanical or neuro-physiological benefit (e.g. by stimulation of joint mechanoreceptors) compared to natural history or the changes in sway observed under analgesic treatment . However, the limitations of the respective included studies do not encourage further hypothesizing about potential underlying mechanisms at this point. At this point, practitioners are discouraged from advertising any effect of manual therapeutic interventions on balance e.g. in fall or injury prevention.