Peak Jump Power Reflects the Degree of Ambulatory Ability in Patients with Mitochondrial and Other Rare Diseases.

Metabolic diseases that lead to neuromuscular, bone, and joint involvement can reduce ambulation and quality of life. Using jumping mechanography, we developed a novel assessment, peak jump power (PJP), and related this to ambulatory ability in patients either having a known or suspected underlying rare disease. From adults and children, we recruited 88 healthy controls and 115 patients (61 with mitochondrial disease and 54 with another diagnosis). Patients were categorized as having no complaints of weakness or ambulation (ambulatory competent; AC), weakness but able to ambulate without aids (ambulatory weakness; AW), or not able to ambulate without aids such as a walker, cane, or wheelchair (ambulatory assistance; AA). Subjects were asked to perform five successive jumps from a squat position. Instantaneous power (W; watts) was calculated and the highest result was divided by the body mass (kg) to calculate PJP (W/kg). Between healthy controls and AC patients, there was no difference in mean PJP (20.5 ± 7.0 W/kg vs. 19.0 ± 7.4 W/kg, p = 0.601; mean ± SD). Progressively lower results were found in patients with AW with a mean PJP of 11.7 ± 5.1 W/kg (p < 0.001 versus AC) and further those with AA with a mean PJP of 5.8 ± 3.2 W/kg (p < 0.001 versus AW). A subgroup analysis of subjects showed that those who did not use ambulatory aids all had a PJP above 10 W/kg. Using this threshold, the receiver operating characteristic curve (ROC) analysis showed PJP to be highly sensitive evaluation of ambulatory ability (sensitivity 95.8%, specificity 52.1%).