Exercise Intervention Research: SpeedGeezer
SpeedGeezer is the name of our experimental speed-based exercise program for people with Parkinson’s disease. It is typically a 6-week program in which participants visit the gym twice per week for 30-minute exercise sessions. This bicycle-based program uses twenty 15-second intervals of fast pedaling to engage the brain and spinal cord in high levels neural excitation. We are training the brain and spinal cord to deliver powerful input to the muscles. When people begin this program, the bike’s resistance is kept at the lowest levels to prevent muscle or joint soreness and to keep cardiovascular strain low. Our participants, who are older adults and people with Parkinson’s disease respond well to this program. There is minimal fall risk and the tests of mobility tend to either improve or not decline over time.
PD: Bradykinesia with Segmented Motor Output
Bradykinesia is defined as slowness of movement and it is one of the symptoms of Parkinson’s disease (PD). We are interested in the use of speed-based exercise to reverse this symptom. When we see slow movements in older adults who have PD, we assume that there are three contributing factors:
- Effects of Parkinson’s disease
- Effects of aging
- Effects of chronic low physical activity levels which are common in affluent western societies like the US.
In our study of Bradykinesia, we use rapid isometric muscular contractions as our research model. In some individuals there is a general slowing in the time to achieve peak muscular force but the force recording is still relatively smooth in appearance. In other individuals, like the one shown in the figure, we see evidence of segmented motor output as the subject tries to reach peak force as quickly as possible. In healthy subjects there are no bumps in this graph and there is smooth rising slope to peak force and a smooth relaxation phase thereafter. Notice in this subject that the rate of force production (the slope of the force time curve) is quite steep up to the blue circles that define the end of the first segment. Thereafter, further increases in force are slower and the curve is additionally segmented. The bumpiness in this graph (segmentation) is related to the disease and not age or activity levels. We continue to work on the analysis of this segmentation with questions about how it might be linked to either tremor or festination of gait (small shuffling steps) and whether segmentation can be reduced with exercise.
Motor Unit Correlates of Power
A motor unit is defined as a single motor neuron and the set of muscle fibers that it innervates. At the level of the motor unit, muscular force is increased by recruiting more motor units and by stimulating them to fire at higher rates. Some of our projects are related to the initial motor unit firing rates during fast muscle contractions. These firing rates are important for rapid movements such as throwing or kicking in sport, some movements involved in physical labor, and responding to slips, trips or unstable surfaces in fall prevention. Regular physical activity and power-based exercise helps to preserve preserve neuromuscular function and mobility throughout the lifespan.