Warm-up prior to undertaking a dynamic psychomotor task: does it aid performance?

AIM: The purpose of this study was to examine the effect of differing types of warm-up on the performance of a psychomotor skill that required quick reaction and movement times (MTs), and whole-body co-ordination. METHODS: Subjects (n=12) carried out a psychomotor task which involved reacting to 1 of 3 lights, then running through a slalom course before kicking a mini-soccer ball at a target. The task was completed following rest, a physical warm-up, a skill-specific warm-up and a skill plus physical warm-up. In the physical, and skill plus physical warm-ups the subjects cycled on an ergometer at a workload calculated to induce exercise at their lactate threshold. The outcome dependent variables were time to initiate a movement (reaction time), time to complete the slalom run (MT) and two measures of passing accuracy(constant error and variable error. Biomechanical variables(knee, hip and ankle angles, and horizontal and vertical ankle velocities at contact(were also compared. RESULTS: A repeated measures analysis of variance showed no significant effect of warm-up type on any of the dependent variables. Stepwise multiple regression analyses showed that changes in heart rate from resting values to those before performance of the skill test (D HR pre-performance) and those after performance of the test (D HR post-performance) combined were significant predictors of MT (R(2)=0.31, P<0.001), while D HR post-performance significantly predicted reaction time (R(2)=0.12, P<0.02). CONCLUSIONS: It was concluded that warm-up provided no significant benefit in performance for a task that was dynamic in nature but that physical arousal probably aids reaction and MTs.

Estimating propulsive forces--sink or swim?

The purpose of this study was to investigate the validity of hydrodynamic force estimation in swimming as calculated by the quasi-static approach. To achieve this a full-scale mechanical arm was developed, built and tested. The mechanical arm, covered with a prosthetic shell and driven at the shoulder was used to simulate a single plane underwater rotation at four elbow configurations. A computer program controlled the shoulder movement to achieve a replicable angular velocity profile for each arm movement. A strain gauge system was used to directly measure the generated arm torque. Repeated trials were conducted at fixed elbow angles of 110 degrees, 135 degrees, 160 degrees and 180 degrees. All trials were filmed using a three-dimensional underwater set-up. Each trial was digitised at 25 Hz and the hydrodynamic drag force profile of the hand calculated using the quasi-static procedure. From these data, the estimated shoulder torque was calculated and compared to the direct measurement of shoulder torque from the mechanical arm. The results showed that the arm produced a repeatable movement through the water. The shoulder torque profiles using the direct measure (the arm) and the indirect measures (quasi-static approach) differed considerably. The quasi-static approach appears not to accurately reflect the hydrodynamic force profile generated by the arm movement in swimming. Furthermore, it seems that the swimmer's hand contribution is overstated in up to date studies. It is essential that the propulsive mechanisms in swimming be further investigated if factors underpinning an optimal technique are to be established.

Effect of incremental exercise on initiation and movement times in a choice response, whole body psychomotor task.

OBJECTIVES: To examine how exercise at moderate and maximal intensities affects performance on a choice response time, whole body psychomotor task. METHODS: Subjects (n = 12) were tested on a three-choice response time task, after rest and after exercise at 70% and 100% maximum power output (W*max). The dependent variables were time to begin forward momentum (initiation time) and time to complete the movement (movement time). Stride time for the first and second strides and number of strides to cover first 1.1 m were also measured. Blood lactate concentrations and heart rate were recorded before and after completion of each psychomotor test. The subjects subjectively assessed the amount of effort that they used to complete the task. RESULTS: Repeated measures analysis of variance showed a significant effect for initiation (F2,22 = 11.47, p < 0.001) and movement times (F2,22 = 14.61, p < 0.001). Post hoc least significant difference (LSD) tests showed that initiation time after exercise at 70% W*max was significantly faster than that in the other two conditions. Speed of initiation after rest was significantly quicker than that after exercise at W*max. For movement time, LSD tests showed that time after maximal exercise was significantly slower than that in the other two conditions. Stride time for the second stride showed a significant effect (F2,22 = 6.20, p < 0.01). LSD tests found that time after exercise at W*max was significantly slower in the other two conditions. Stepwise multiple regression analyses found that the increment of change, from rest, of lactate concentrations could significantly predict the increment of change in initiation (R2 = 0.40) and movement (R2 = 0.50) times. CONCLUSIONS: Exercise affects a whole body task differently from purely cognitive tasks. Central factors are probably more important than peripheral factors.

Accuracy evaluation of an on-line kinematic system via dynamic tests.

The study presents an experimental methodology for evaluating the accuracy and reliability of the kinematic data collection of an on-line optoelectronic system used in biomechanics studies. The methodology is based on a series of dynamic tests using an independently measured and controlled frequency input varying systematically five different factors--(1) camera-object distance, (2) distance from calibrated field, (3) size of the calibration field, (4) position in the calibration field and (5) rotation speed. The proposed methodology is addressed mainly towards medical related research or biomechanical analysis of human joints where a high degree of accuracy is of prime importance. It is used to evaluate the ELITE motion analysis system. The results of the study showed that the error distribution is sensitive to relatively small changes of the first four factors as the error magnitude was not affected strongly remaining within 2% of the object length for the majority of the experiments.