Developing Strategies to Optimize the Exercise Response After Tetraplegia.

Part I. This study will examine the relationship between steady-state and peak exercise performance in participants with tetraplegia or paraplegia. Participants will have their peak energy expenditure measured using a discontinuous step test. Participants will then perform three different trials of exercise at a steady state at a target intensity that corresponds with 90%, 70%, and 60% of their own measured peak energy expense. Participants will exercise at the prescribed power output until fatigue. Participants may choose which exercise mode they use (with all steady-state trials being in the same mode as the peak test), and may choose to perform the study twice in the different exercise modes. Exercise trials will be performed over a number of different sessions in a randomized order, allowing for adequate rest and recovery between trials, and depending on each participant's capabilities and preferences. Part II. This study will determine if high intensity interval training (HIIT) results in greater energy expense than constant rate aerobic exercise, and will test if exercising with HITT effects time to fatigue. Participants will exercise using a high intensity interval training (HIIT) protocol, which involves alternating high intensity bouts of short duration with low intensity bouts of longer duration. Participants will have their peak energy expenditure measured using a discontinuous step test. Participants will then perform one trial of steady-state exercise at a target intensity that corresponds with 50% of their peak energy expense, for a target of 20-45 minutes. Participants will perform a separate trial using a HIIT protocol of exercise at a target intensity that corresponds with 50% of their peak energy expense interspersed with bouts of high intensity (target intensity that corresponds with 90% of peak energy expense) for 30-60 seconds, for a total duration target of 20-45 minutes. Participants may choose which exercise mode they use (with all trials being in the same mode as the peak test), and may choose to perform the study twice in the different exercise modes. Exercise trials will be performed over a number of different sessions in a randomized order, allowing for adequate rest and recovery between trials, and depending on each participant's capabilities and preferences.

We will test whether introducing HITT into an acute exercise bout will increase overall energy expenditure or time to fatigue.

Inclusion Criteria: Spinal cord injury of at least one year duration, C5-T12, ASIA impairment scale (AIS) A-D Aged 18-75 years for the duration of the study participation Medically stable and healthy enough to engage in and complete exercise requirements Willing and able to complete the exercise protocols and testing requirements Able to understand and follow written and verbal instructions from study staff Able to communicate with study staff about their exercise capabilities and preferences Exclusion Criteria: Current serious injury(ies) of the upper extremities Known cardiovascular disease Unsatisfactory results of EKG screening Implanted electronic cardiac device (e.g. pace maker, defibrillator, etc.) Current pressure ulcer(s) Morbid obesity Known thyroid dysfunction Current cancer Current uncontrolled high blood pressure ( > 140/90 mmHg) Uncontrolled epilepsy Current deep vein thrombosis Ventilator-dependent Cognitive impairment