Electromyographic Responses of Neck, Back, and Limb Outlet Muscles Associated With High-Velocity, Low-Amplitude Manual Cervical and Upper Thoracic Spinal Manipulation of Individuals With Mild Neck Disability: A Descriptive Observational Investigation.

OBJECTIVES: The purpose of this study was to investigate the extent of electromyographic responses associated with manual high-velocity, low-amplitude (HVLA) spinal manipulation systematically applied to the upper and lower cervical and upper thoracic spines in a cohort with mild neck disability. METHODS: The study was a descriptive observational investigation, with all participants receiving the same interventions. Nineteen participants with mild neck disability received 6 manual HVLA manipulations to the cervical and upper thoracic spine. Bipolar surface electromyography electrode pairs were used to measure responses of 16 neck, back, and limb outlet muscles bilaterally. The number of electromyographic responses was then calculated. RESULTS: Electromyographic responses associated with cervical and thoracic manipulation occurred in a median of 4 of the 16 (range: 1-14) recorded muscles. Cervical spinal manipulation was associated with the highest rates of electromyographic responses in neck muscles, whereas responses in back muscles were highest after upper thoracic manipulation. CONCLUSION: Cervical spinal manipulation was associated with the highest rate of electromyographic responses in muscles of the cervical spine (sternocleidomastoid and splenius cervicis), whereas responses in back muscles (upper and middle trapezius, latissimus dorsi, and longissimus thoracis) were highest after upper thoracic manipulations. This result suggests that electromyographic muscular responses associated with spinal manipulation primarily occur locally (close to the target segment) rather than distally.

Contractile history affects sag and boost properties of unfused tetanic contractions in human quadriceps muscles.

PURPOSE: A period of extra-efficient force production ("boost") followed by a decline in force ("sag") is often observed at the onset of unfused tetanic contractions. We tested the hypothesis that in human muscle boost and sag are diminished in repeated contractions separated by short rest periods and are re-established or enhanced following long rest periods. METHODS: Two sets of 3 unfused tetanic contractions were evoked in the right quadriceps muscle group of 29 participants via percutaneous stimulation of the femoral nerve. Contractions consisted of 20 pulses evoked at inter-pulse intervals of 1.25 × twitch time to peak torque. Contractions were evoked 5 s apart and sets were evoked 5 min apart. RESULTS: The ratio of the angular impulse of pulses 1-10 to the angular impulse of pulses 11-20 was used as the boost indicator. By this metric, boost was higher (P < 0.05) in the first relative to the second and third contractions within a set, but did not differ between sets (Set 1: 1.31 ± 0.15, 1.18 ± 0.12, 1.14 ± 0.12 vs Set 2: 1.34 ± 0.17, 1.17 ± 0.13, 1.14 ± 0.13). Sag (the percent decline in torque within each contraction) was also higher (P < 0.05) in the first relative to the second and third contractions within a set, but did not differ between sets (Set 1: 40.8 ± 7.5%, 35.4 ± 6.8%, 33.2 ± 7.8% vs Set 2: 42.1 ± 8.0%, 35.5 ± 6.8%, 33.9 ± 7.2%). Participants' sex and resistance training background did not influence boost or sag. CONCLUSION: Boost and sag are sensitive to contractile history in whole human quadriceps. Optimizing boost may have application in strength and power sports.

Is There an Optimal Pole Length for Double Poling in Cross Country Skiing?

The aim of this study was to determine the effects of pole length on energy cost and kinematics in cross country double poling. Seven sub-elite male athletes were tested using pole sets of different lengths (ranging between 77% and 98% of participants' body height). Tests were conducted on a treadmill, set to a 2% incline and an approximate racing speed. Poling forces, contact times, and oxygen uptake were measured throughout the testing. Pole length was positively correlated with ground contact time (r = .57, p < .001) and negatively correlated with poling frequency (r = -.48, p = .003). Pole length was also positively correlated with pole recovery time and propulsive impulse produced per poling cycle (r = .36, p = .031; r = .35, p = .042, respectively). Oxygen uptake and pole length were negatively correlated (r = -.51, p = .004). This acute study shows that increasing pole length for double poling in sub-elite cross country skiers under the given conditions seems to change the poling mechanics in distinct ways, resulting in a more efficient poling action by decreasing an athlete's metabolic cost.

Active control of static pedal force direction decreases maximum isometric force output.

Perfect mechanical force effectiveness in cycling would be achieved if the forces applied to the pedal were perpendicular to the crank throughout the full crank cycle. However, empirical observations show that resultant pedal forces display substantial radial components in recreational and even highly-trained elite cyclists. Therefore, we hypothesized that attempting to maximize mechanical effectiveness during the entire downstroke of the pedal cycle must be associated with a penalty that outweighs the benefits of perfect effectiveness. Twenty recreational cyclists performed maximum isometric voluntary contractions at five static crank positions in the downstroke phase of cycling for two testing conditions: (i) a non-constrained (NC) condition, where athletes were asked to produce the maximum force possible on the pedal without consideration of the force direction and (ii) a constrained (C) condition, with the instruction to produce maximal pedal forces perpendicular to the crank. Resultant force and effective force (force perpendicular to the crank in the NC conditions) were compared to the force in the C condition that was, by definition, perpendicular to the crank. Maximum effective force in the NC condition was greater (mean = 50 %, range = 38-69 %) than for the C condition across all crank positions. Applying forces perpendicular to the crank in the downstroke of the pedal cycle resulted in severe reductions in force magnitude, suggesting that coaches and athletes should not attempt to change cycling technique towards perfect force effectiveness.

Development of the instrumentation of a 4-man bobsled.

A bobsled race can be won or lost at the start, and the contribution of the athletes during the start phase is crucial. Nevertheless, the details of that contribution are not well understood, and we believe that, to improve team performance, it is necessary to determine the contributions of the individual athletes to the bobsled's speed throughout the start phase. The goal of this project was to develop the instrumentation for a 4-man bobsled that allows for measuring the propulsive forces of each athlete during the bobsled push start. We describe the final set-up and discuss potential applications. The instrumented bobsled can be used to provide novel and important information about individual athlete and team performance during the start phase of bobsledding.