The kidneys are important at getting rid of toxins and excess water from the body. If they fail, then toxins and excess water builds up within the body. Kidney failure is treated by either giving patients a new kidney (a transplant) or by removing the toxins and fluid from the body by the process of dialysis.

The investigators' aim is to personalise the care given to patients with kidney failure, and as such, they have started measuring the fitness of patients with kidney failure, who either already require dialysis or may need dialysis in the near future. This is currently done in a number of ways including measuring how strong their grip is, assessing their walking speed and asking questions about how difficult they find certain activities.

In the future, the investigators think that this will allow targeted treatments to help improve their fitness and potentially identify any problems earlier.

Current approaches to measuring activity and fitness have limitations and in particular may over- or underestimate the level of the physical activity. To over come these limitations, participants will be asked to wear an activity tracker (called an accelerometer) on for a week. Readings from the accelerometer will be compared against the other markers of fitness and activity to see if they are comparable. It will also be noted whether patients are prepared to wear the device for 7 days (compliance).

Inclusion Criteria:

1. Aged over 18 years with low clearance pre-dialysis and referred to the Low Clearance Clinic with estimated Glomerular Filtration Rate (eGFR) less than 20 ml/min/1.73m and / or commenced on haemodialysis
2. Able to give informed consent

Exclusion Criteria:

1. Significant resting tremor of any aetiology or severe Parkinson's Disease
2. Immobile
3. Arteriovenous fistulas in both arms
4. Any scheduled inpatient treatment or day case treatment in next 7 days.

Low clearance pre-dialysis patients referred to the Low Clearance Clinic and / or who have commenced on haemodialysis