Biomedical subjects

Harm Kuipers

Publications and source records attributed to Harm Kuipers.

5 recordsLinked to original sources

PubMed2003

Distractor interference in selective reaching: dissociating distance and grouping effects.

In the present experiment, the authors sought to differentiate between a distance and a grouping explanation for the symmetric versus asymmetric patterns of distractor interference in selective reaching. Participants (N = 16) pointed to a green target that appeared either with or without a red distractor. Target-distractor separation was manipulated within an array of 5 closely grouped stimulus boxes, and distractor interference (difference in performance between trials with and trials without a distractor) was measured in reaction time, movement time, percentage errors, and movement endpoints. Small distances (5 mm) between target and distractor yielded a symmetric pattern of interference, whereas large distances (20 mm) yielded an asymmetric pattern, with more interference from near than from far distractors. Those findings support the distance account of distractor interference and refute the grouping account.

Adult↗

PubMed2002

Immediate and long-term effects of ankle-foot orthosis on muscle activity during walking: a randomized study of patients with unilateral foot drop.

OBJECTIVES: To determine (1) whether use of an ankle-foot orthosis (AFO) by patients with ankle dorsiflexor paresis leads to decreased muscle activity, immediately or 6 weeks after AFO use, and (2) whether this decrease (if present) differs between healthy and paretic subjects. DESIGN: Cross-sectional and longitudinal randomized case-control study. SETTING: Rehabilitation research center in the Netherlands. PARTICIPANTS: Fourteen healthy persons and 29 patients with foot drop. INTERVENTIONS: Muscle activity was measured by surface electromyography. Electromyographic reproducibility was tested in 14 healthy volunteers walking with and without AFO. Acute changes in muscle activity from AFO use were compared between the 14 healthy persons and the 29 patients with foot drop. Adaptation effects of AFO use after 6 weeks were studied in 29 patients, randomly chosen 16 of whom had started using an AFO at the first measurement. MAIN OUTCOME MEASURES: Amount of change in mean rectified electromyographic activity (delta value) between walking with and without AFO. Follow-up measurements were conducted after 3 and 6 weeks. RESULTS: Correlation coefficients, reflecting within-subject reproducibility, varied between.68 and.96 (mean,.86). In patients and healthy subjects, tibialis anterior muscle activity decreased by 7% and 20% (P = .01, P = .04), respectively, when using an AFO. In patients, this decrease was measured in the overall activity during the gait cycle; in healthy subjects, it was measured in the first 15% of the gait cycle. Overall electromyographic activity did not change during 6 weeks; delta values per muscle did not change during follow-up in the AFO group. CONCLUSION: AFO use immediately reduced muscle activity of the ankle dorsiflexors. However, using an AFO for 6 weeks did not lead to a generally lower electromyographic activity level nor did the amount of activity reduction accumulate in comparison with patients who did not use an AFO. It is, therefore, safe to use an AFO, even with recently paretic patients.

Adult↗

PubMed2002

Selective reaching: evidence for multiple frames of reference.

Students participated in 3 experiments investigating the use of environment- and action-centered reference frames in selective reaching. They pointed to a green target appearing either with or without a red distractor. Target-distractor distance was manipulated, and distractor interference (difference between distractor trials and no-distractor trials) was measured in reaction time, movement time, and movement endpoint. Target-distractor distance determined the dominant frame of reference. Small distances evoked an environment-centered framework that encoded targets within an external context. Large distances evoked an action-centered framework that encoded targets relative to the start position of the hand. Results support the hypothesis that the brain represents spatial information in multiple frames of reference, with the dominant frame of reference being dependent on the task demands.

Adolescent↗

PubMedDate not supplied

Effects of oral bovine colostrum supplementation on serum insulin-like growth factor-I levels.

OBJECTIVES: We investigated whether supplementation with 60 g/d of bovine colostrum affects blood levels of insulin-like growth factor-I (IGF-I) and IGF binding protein-3 in relation to doping testing. Nine endurance-trained men ingested 60 g/d of bovine colostrum for 4 wk. METHODS: Blood and urine were sampled before starting supplementation. After 4 wk urine and blood samples were taken after an overnight fast and 2 h after ingestion of the last portion to study possible acute effects. RESULTS: Blood IGF-I levels before supplementation were (mean +/- standard deviation) 31 +/- 13 nM/L, and no acute effects were observed after 4 wk of supplementation (33 +/- 9 nM/L). Levels of IGF-binding protein-3 were 136 +/- 11 nM/L before supplementation and 135 +/- 16 nM/L after 4 wk of supplementation. Two hours after ingestion of the last portion, the level of IGF binding protein-3 was 131 +/- 19 nM/L, which was not different from baseline values. Drug testing in a laboratory accredited by the International Olympic Committee did not show any forbidden substance before or after 4 wk of supplementation. CONCLUSIONS: Daily supplementation with 60 g of bovine colostrum for 4 wk does not change blood IGF-I or IGF binding protein-3 levels and does not elicit positive results on drug tests.

Adult↗

PubMedDate not supplied

The incidence of injuries in elite junior figure skaters.

BACKGROUND: There has been rapid growth in the technical and physiologic demands made on skaters who perform more and more difficult jumps, spins, lifts, throws, and free skating movements. PURPOSE: To investigate the frequency of injuries and overuse syndromes in elite junior skaters. STUDY DESIGN: Questionnaire. METHODS: During four consecutive Junior World Figure Skating Championships and the Croatia Cup, we interviewed 236 female and 233 male skaters by questionnaire to determine the frequency of injuries and overuse syndromes. RESULTS: Fifty-nine of the female skaters (25%) and 65 of the male skaters (27.9%) reported sustaining acute injuries; 101 female (42.8%) and 106 male (45.5%) skaters reported overuse syndromes. Low back pain was reported by 19 female and 23 male skaters. The most frequent acute injury was ankle sprain. In singles female skaters, the most frequent overuse injury was stress fracture (19.8%), followed by jumper's knee (14.9%). In singles male skaters, jumper's knee (16.1%) was the most frequent injury, followed by Osgood-Schlatter disease (14.2%). More than 50% of injuries in young singles figure skaters involved overuse syndromes. Pairs skaters and ice dance skaters had a higher risk of acute injury than overuse syndrome because of falls from lifts and throw jumps. CONCLUSIONS: Programs to improve postural alignment, flexibility, and strength, especially during the asynchronous period of bone and soft tissue development, should be instituted to prevent and reduce overuse syndromes.

Adolescent↗