Upper extremity freezing and dyscoordination in Parkinson's disease: effects of amplitude and cadence manipulations.

Purpose. Motor freezing, the inability to produce effective movement, is associated with decreasing amplitude, hastening of movement, and poor coordination. We investigated how manipulations of movement amplitude and cadence affect upper extremity (UE) coordination as measured by the phase coordination index (PCI)-only previously measured in gait-and freezing of the upper extremity (FO-UE) in people with Parkinson's disease (PD) who experience freezing of gait (PD + FOG), do not experience FOG (PD-FOG), and healthy controls. Methods. Twenty-seven participants with PD and 18 healthy older adults made alternating bimanual movements between targets under four conditions: Baseline; Fast; Small; SmallFast. Kinematic data were recorded and analyzed for PCI and FO-UE events. PCI and FO-UE were compared across groups and conditions. Correlations between UE PCI, gait PCI, FO-UE, and Freezing of Gait Questionnaire (FOG-Q) were determined. Results. PD + FOG had poorer coordination than healthy old during SmallFast. UE coordination correlated with number of FO-UE episodes in two conditions and FOG-Q score in one. No differences existed between PD-/+FOG in coordination or number of FO-UE episodes. Conclusions. Dyscoordination and FO-UE can be elicited by manipulating cadence and amplitude of an alternating bimanual task. It remains unclear whether FO-UE and FOG share common mechanisms.

Comparison of three baseball-specific 6-week training programs on throwing velocity in high school baseball players.

Throwing velocity is an important baseball performance variable for baseball pitchers, because greater throwing velocity results in less time for hitters to make a decision to swing. Throwing velocity is also an important baseball performance variable for position players, because greater throwing velocity results in decreased time for a runner to advance to the next base. This study compared the effects of 3 baseball-specific 6-week training programs on maximum throwing velocity. Sixty-eight high school baseball players 14-17 years of age were randomly and equally divided into 3 training groups and a nontraining control group. The 3 training groups were the Throwers Ten (TT), Keiser Pneumatic (KP), and Plyometric (PLY). Each training group trained 3 d·wk(-1) for 6 weeks, which comprised approximately 5-10 minutes for warm-up, 45 minutes of resistance training, and 5-10 for cool-down. Throwing velocity was assessed before (pretest) and just after (posttest) the 6-week training program for all the subjects. A 2-factor repeated measures analysis of variance with post hoc paired t-tests was used to assess throwing velocity differences (p < 0.05). Compared with pretest throwing velocity values, posttest throwing velocity values were significantly greater in the TT group (1.7% increase), the KP group (1.2% increase), and the PLY group (2.0% increase) but not significantly different in the control group. These results demonstrate that all 3 training programs were effective in increasing throwing velocity in high school baseball players, but the results of this study did not demonstrate that 1 resistance training program was more effective than another resistance training program in increasing throwing velocity.

Vibration elicits involuntary, step-like behavior in individuals with spinal cord injury.

BACKGROUND: Impaired walking is a debilitating consequence of spinal cord injury (SCI). This impairment arises, to some degree, from disruption of supraspinal pathways that activate the spinal locomotor central pattern generator (CPG). Evidence in nondisabled (ND) individuals suggests that vibration activates locomotor CPGs, eliciting involuntary step-like behavior. OBJECTIVE: To compare vibration-elicited step-like behavior in individuals with chronic SCIs with the responses of ND individuals and to assess the influence of locomotor training on these responses. METHODS: Participants included 7 individuals with motor-incomplete SCIs (MISCIs) and 6 with motor-complete SCIs (MCSCIs) who were untrained, 6 individuals with MISCIs who underwent locomotor training, and 8 ND individuals. Kinematic and EMG data were collected while vibration was applied to the quadriceps, hamstrings, or tensor fascia latae (TFL) muscles. Consistency and robustness of vibration-elicited responses was determined from hip and knee angle data. RESULTS: Consistent and reliable step-like behaviors were elicited in individuals with MISCIs and MCSCIs, although responses were not as robust as those in ND individuals. Vibration to the TFL elicited the most robust responses. Consistency and robustness were not influenced by SCI severity or locomotor training but appeared to increase with repeated testing. CONCLUSION: These results confirm that vibration elicits step-like behaviors in individuals with SCIs, even those with no voluntary motor function in the legs. Further research is warranted to investigate the use of vibration as an approach to activating the spinal CPGs associated with stepping, perhaps as an adjunct to locomotor training for individuals with SCIs.

Inotropic effects of the K+ channel blocker 3,4-diaminopyridine on fatigued diaphragm muscle.

K(+) channels play important roles in skeletal muscle contraction by regulating action potential duration. Blocking these channels, for example with 3,4-diaminopyridine (DAP), augments muscle force considerably, and these force increases are maintained well during fatigue-inducing contractions. The present study tested the hypothesis that K(+) channel blockade also improves force of previously fatigued muscle. Rat diaphragm underwent fatigue-inducing stimulation in vitro with four different stimulation protocols consisting of 20 Hz vs. 50 Hz trains and 1 min vs. 4 min stimulation durations. DAP administered at the onset of the recovery period produced significant force increases irrespective of the amount of antecedent force loss. These force gains considerably exceeded those resulting from normal force recovery in untreated muscle. Furthermore contraction time was prolonged by DAP in all cases, and half-relaxation time was prolonged by DAP in most cases. Several differences were found compared with previous studies of DAP in fresh muscle, including smaller magnitude and slower time course of force increases. Intracellular electrophysiological recordings found smaller effects of DAP on action potential overshoot and time-depolarization integral in previously stimulated compared with fresh muscle. These data indicate that K(+) channel blockade does indeed increase force of fatigued diaphragm, but to an attenuated extent relative to its effects on non-fatigued muscle, which can be explained on the basis of electrophysiological findings. Nonetheless DAP-induced force increases were usually sufficient to restore force to values present prior to the onset of fatigue-inducing stimulation.