Open Access

Sponsorship bias could affect research results to inform decision makers when using the results of these trials. The extent to which sponsorship bias affect results in the field of physical therapy has been unexplored in the literature. Therefore, the main aim of this study was to evaluate the influence of sponsorship bias on the treatment effects of randomized controlled trials in physical therapy area.

Background: Neck pain is one of the most common musculoskeletal pains and among the fourth leading causes of years of life lost due to disability, following back pain, depression, and arthralgia. (1) In the course of their lives, about 70% of all people will experience a clinically relevant episode of neck pain, (2) so finding a good therapy to treat it is of high interest. Aerobic exercise is associated with pain reduction in patients with different types of MSK pain. Recent studies have shown a positive impact of aerobic exercises on brain function, memory processing, cognition, and motor function. (3, 4) Therefore, the influence of aerobic exercise on pain modulation seems to be of particular interest for individuals with chronic MSK pain, since brain imaging studies have shown that these patients have structural and functional changes, as well as abnormal brain features in various areas of the brain. The evidence regarding the effectiveness of aerobic exercise for neck pain seems limited and outdated. Thus, a systematic review evaluating the effects of aerobic exercise in patients with neck pain is needed. Therefore, this review aims to investigate the effectiveness of aerobic exercise interventions when compared to other conservative and non-conservative interventions (e.g., localized exercises, medication, acupuncture, physical agents, manual therapy) to decrease pain intensity in people with neck pain. Materials and methods: Electronic literature searches were conducted in a total of six databases such as Medline, Embase, CINAHL, Cochrane Library, Web of Science, and Scopus. The review considered randomised controlled trials (RCTs) including patients over 18 years having musculoskeletal pain in the neck area. The Neck Pain Task Force's classification of pain severity describes four levels of neck pain, with the first three levels considered in this review. (5)These must be clinically diagnosed by a health care provider according to signs and symptoms or based on standardized criteria specific for each disease. Studies involving subjects with any pre-existing conditions, previous surgery, or pain not clearly related to the musculoskeletal system were excluded. No limits were applied in terms of sex, ethnicity, and living country. Data were extracted using a standardized data extraction form. Methodological quality was determined using the Cochrane Collaboration Risk of Bias Tool (CCRBT) and the strength of the evidence with Grading of Recommendations Assessment, Development, and Evaluation (GRADE). Data were extracted and evaluated by two independent reviewers. Results: A total of 21585 records were identified and screened independently for eligibility by two reviewers. A total of six unique studies, reported on ten manuscripts met the specified inclusion criteria. Different types of aerobic exercise were used in the studies. Studies included isolated and combined aerobic exercise using interventions such as cycling on an ergometer or walking outdoors at a moderate intensity. Comparison groups were for example strength training or education. The most common outcome was pain assessed with the Visual Analogue Scale (VAS) or the Nordic questionnaire. The included studies had a high risk of bias and the overall quality of the evidence for this systematic review was considered low. There was high heterogeneity in the included studies regarding interventions applied and study results. When looking at the effect of aerobic exercise versus control group or other intervention groups measured with VAS, it can be observed, that there was a great heterogeneity between studies results (different magnitudes and directions). Although none of the comparisons showed a statistically significant difference between aerobic exercise and control (MD 6.24 mm, 95% CI [-11.21; 23.96]) or active intervention groups (MD -9.52 mm, 95% CI [-18.48; -0.56]) on pain intensity; it seems that aerobic exercise is slightly better than a control group, and equally effective as other active treatments such as strength exercise or education. In addition, when combined with other therapeutic modalities, aerobic exercise, could potentially help to reduce pain intensity (MD 7.71 mm, 95% CI [1.07; 14.35]). Especially in the long term, the combination of strength and aerobic exercise showed promising results. Statistically significant differences in favour of aerobic exercise for pre vs. three months follow up (MD 11.20 mm, 95% CI [2.85;19.55]) and pre vs. six moths follow up (MD 15.10 mm, 95% CI [6.99; 23.21]) were found. Conclusions: Although there is currently limited evidence on the effectiveness of aerobic exercise in individuals with chronic neck pain, aerobic exercise was found to not only reduce pain intensity, but also to improve disability as well as physical and emotional functioning. However, as the evidence is limited, low quality, and heterogeneous, further research is needed in this area to obtain more accurate results.

Bias is a systematic error that can cause distorted results leading to incorrect conclusions. Intervention bias (i.e., contamination bias, cointervention bias, compliance bias, and performance bias) and detection bias are the most common biases in rehabilitation research. A better understanding of these biases is essential at all stages of research to enhance the quality of evidence in rehabilitation trials. Therefore, this narrative review aims to provide insights to the readers, clinicians, and researchers about contamination, cointervention, compliance, performance, and detection biases and ways of recognizing and mitigating them. The literature selected for this review was obtained mainly by compiling the information from several reviews looking at biases in rehabilitation. In addition, separate searches by biases and looking at reference lists of selected studies as well as using Scopus forward citation for relevant references were used. This review provides several strategies to guard against the impact of bias on study results. Clinicians, researchers, and other stakeholders are encouraged to apply these recommendations when designing and conducting rehabilitation trials.

Methods: Systematic review of randomized controlled trials (RCT). Searches were conducted in five electronic databases. Studies were selected if they included patients with NP over 18 years old treated with aerobic exercise (AE) (e.g., cycling, running, hiking, and walking). The main outcome of interest was pain intensity. Qualitative and quantitative data were extracted. The risk of bias (RoB) was determined using the Cochrane RoB Tool-2 and the overall certainty of the evidence with the GRADE recommendations. Results: Out of 21,585 initial records screened, a total of six individual studies published in ten manuscripts were included. There was a great heterogeneity between protocols, comparisons, and studies’ results (different magnitudes and directions). When looking at the effect of aerobic exercise versus control groups or other interventions on pain intensity measured with the VAS, not statistically (nor clinical) significant differences between aerobic exercise and control groups (MD [95%CI] 5.16 mm [-6.38, 16.70]) were identified. The combined effect of AE plus other interventions seems to be effective. Strength exercise obtained better effects than aerobic exercises (MD [95%CI]: -11.34 mm [-21.6, -1.09]). Conclusions: Aerobic exercise presented positive results to reduce pain intensity, and improving disability, and physical and emotional functioning. However, the evidence is restricted, low quality, and heterogeneous.