This laboratory study investigated seated computer work before and after prolonged constrained sitting. Discomfort ratings and kinetic and kinematics data were recorded in nine healthy males performing computer work for 5 min before and after 96 min of sitting. The displacement of the center of pressure (CoP) in anterior-posterior and medial-lateral directions and lumbar curvature (LC) were calculated. The root mean square, standard deviation, and sample entropy values were computed from the CoPs and LC signals to assess the magnitude, amount of variability, and regularity of sitting dynamics, respectively. The discomfort increased for the buttocks (p = .02).The standard deviation and sample entropy values of the CoPs and LC signals, respectively, increased (p < .04) and decreased (p < .004) whereas the root mean square remained unchanged (p > .15) after prolonged constrained sitting compared with before. This present study showed that during seated computer work, prolonged constrained sitting affected the amount of variability and the regularity of sitting postural control, whereas the magnitude was not affected. The importance of the dynamics of sitting control may challenge the idea of a static and ideal seated posture at work.
Ernst A. Hansen, Michael Voigt, Uwe G. Kersting and Pascal Madeleine
In the current study we investigated changes in voluntary rhythmic leg movement frequency (freely chosen cycling cadence) and rhythmic movement pattern (tangential pedal force profile) after fatiguing hip flexion and hip extension exercises. Nine healthy individuals performed ergometer cycling at freely chosen cadence and at a cadence of 1 Hz before and after fatiguing hip flexion and hip extension exercises. The freely chosen cadence was not affected after fatiguing exercises. An alteration of key characteristics of the tangential pedal force profile was found during cycling at a cadence of 1 Hz after hip flexion exercise. Thus, minimum tangential pedal force decreased by 12.0 ± 11.3% (p = .006), while maximum tangential pedal force increased by 4.6 ± 4.2% (p = .011), and the phase with negative tangential pedal force increased by 2.6 ± 3.2% (p = .040). In conclusion, novel information was obtained on aspects of rhythmic leg movement behavior in form of pedaling after fatiguing exercise.
Mark Holten Mora-Jensen, Pascal Madeleine and Ernst Albin Hansen
The present study analyzed (a) whether a recently reported phenomenon of repeated bout rate enhancement in finger tapping (i.e., a cumulating increase in freely chosen finger tapping frequency following submaximal muscle activation in the form of externally unloaded voluntary tapping) could be replicated and (b) the hypotheses that the faster tapping was accompanied by changed vertical displacement of the fingertip and changed peak force during tapping. Right-handed, healthy, and recreationally active individuals (n = 24) performed two 3-min index finger tapping bouts at freely chosen tapping frequency, separated by 10-min rest. The recently reported phenomenon of repeated bout rate enhancement was replicated. The faster tapping (8.8 ± 18.7 taps/min, corresponding to 6.0 ± 11.0%, p = .033) was accompanied by reduced vertical displacement (1.6 ± 2.9 mm, corresponding to 6.3 ± 14.9%, p = .012) of the fingertip. Concurrently, peak force was unchanged. The present study points at separate control mechanisms governing kinematics and kinetics during finger tapping.