# Test-Retest Reliability of Kinematic Parameters of Timed Up and Go in People with Type 2 Diabetes
## 1 Introduction  
Diabetes mellitus (DM) is a chronic disease defined as a state of hyperglycaemia in fasting or postprandial states [1]. DM is one of the largest global public health problems and affects approximately 415 million people in the world among adults aged 20-79 years-old. It is estimated that, in the year 2040, there will be 642 million persons (confidence interval 521-829 million) with DM in the world [2]. The International Diabetes Federation also estimates that, globally, 46.5% of people suffering from diabetes were still undiagnosed in 2015, which may markedly increase the reported prevalence. According with the American Diabetes Association (ADA), the total costs for diabetes care in the United States were approximately 245 billion dollars due to medical costs, lost productivity and disability [3]. Much of the burden of this disease comes from vascular complications, which include cardiovascular disease, retinopathy and nephropathy. Another complication is diabetic peripheral neuropathy, affecting more than 50% of long-term diabetic cases [4].  
Diabetic neuropathy is characterised by progressive degeneration that primarily affects small-diameter cutaneous nociceptive fibres [5]. It may also affect motor fibres, which can cause muscular weakness. In this regard, persons with DM have a reduction of 17% and 14% in the strength of the flexor and extensor muscles of the knee, respectively [6]. Somatosensory feedback is a relevant factor to maintain balance and there is strong evidence showing that diabetic neuropathy affects this source of information, leading to alterations in postural and gait performance [7]. In this regard, previous studies have demonstrated that the main sources of deterioration in the balance in persons with type 2 DM (T2 DM) are deficits in the proprioception of the foot and the ankle [8], or a loss of sensitivity in the feet [9].  
The neurologic exam of the lower limb is the most important aspect in the clinical diagnosis of diabetic neuropathy [10]. The loss of foot vibration perception is associated with an increased risk of foot ulceration in people with diabetes [11]. In this regard, [PERSON] et al. [12] showed that each one-unit increment in the foot vibration threshold increases the risk of foot ulceration by more than 5% in a single year period. Therefore, the foot vibration threshold is a very relevant variable in the diabetic population.  
Previous studies have demonstrated a relationship between the foot vibration threshold and the risk of falling [13], gait speed [14] and mobility disability [15]. Although balance and mobility tests are of great interest in DM studies due to the association with the risk of falling and the ability to perform activities of daily living, a recent systematic review showed that there is a lack of studies evaluating the properties of these tests when they are conducted in the diabetic population [16].  
Therefore, the main objective of this study was to evaluate the test-retest reliability of the kinetic and kinematic parameters obtained from one of the most widely used tests for assessing balance and mobility, the timed up and go (TUG), in people suffering from T2 DM. The second objective was to calculate the reliability of TUG according to the severity of peripheral neuropathy (assessed through an evaluation of the foot vibration threshold).