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Biomedical subjects

C Hertogh

Publications and source records attributed to C Hertogh.

10 recordsLinked to original sources
PubMed2004

Time-of-day effects in maximal anaerobic leg exercise in tropical environment: a first approach.

The aim of this study was to establish the effect of time of day on maximal anaerobic leg power in a tropical environment (French West Indies). Twenty-three physical education students (15 males and 8 females) who trained 10.5 hours a week (SD 6) volunteered to participate in the study. Their mean age, height and body mass were 22.8 (SD 3) years, 172.6 (SD 8) cm, and 64.6 (SD 7) kg, respectively. The chronotype of all subjects was moderate or intermediate. Tests were scheduled at 08 : 00, 13 : 00 and 17 : 00 hours on separate days in random order and constant conditions (room temperature: 28.1 degrees C [SD 0.6], relative room humidity: 62.6 % [SD 3.4]). On test days, the subjects were first measured at rest for body mass, heart rate and rectal temperature and they then performed vertical jump tests and a force-velocity test. The results showed a time-of-day effect on rectal temperature, which was significantly (p < 0.005) higher by the afternoon (13 : 00 and 17 : 00) than the morning (08 : 00). However, our results failed to show any daytime variation in maximal anaerobic power under the influence of tropical climate, which suggests that a hot and humid environment may have blunted the time-of-day effect by a passive warm-up effect.

Adult↗
PubMed2004

Effects of 8 days acclimation on biological and performance response in a tropical climate.

BACKGROUND: This study was designed to determine the acclimation process elicited by exposure to a tropical climate. METHODS: Nine triathletes performed 3 outdoor indirect continuous running multistage tests in both thermoneutral and tropical conditions. Before travelling to the tropical area (Martinique Island, FWI), the triathletes performed the thermoneutral test (TN) in 14 degrees C and 45% rh conditions. The tropical tests were performed 2 and 8 days after arrival (T2 and T8, performed at a mean environmental temperature of 33.4 degrees C and 75.5% rh). The day before T8, blood samples were drawn for biochemical analysis. During each test, tympanic temperature, sweat rate, weight loss, heart rate (HR), and performance were recorded. RESULTS: The results demonstrated that: 1) the mean tympanic temperature was greater in T2 (p<0.001) and T8 (p<0.01) than in TN; 2) the mean sweat rate was significantly greater (p<0.001) in T2 and T8 than in TN and significantly greater in T8 than in T2 (p<0.03); 3) the weight loss after trials was significantly greater (p<0.001) in T2 and T8 than in TN and in T8 than in T2 (p<0.04); 4) the mean HR and the HR at rest were significantly greater in T2 than in TN (p<0.001) and T8 (p<0.005); 6) significant reductions were observed in T8 vs TN in red cell count (p<0.05) and plasma proteins (p<0.04), the consequence of a 7.5% plasma volume expansion; and 7) the performance was significantly lower in both T2 (p<0.02) and T8 (p<0.03) than in TN. CONCLUSIONS: We concluded that 8 days exposure to hot/wet conditions induced impairments in physiological responses and performance that were still evident on the 8th day. Further and longer outdoor studies are needed to investigate if return to optimal performance levels after adaptation to hot/wet conditions is possible.

Acclimatization↗
PubMed2003

Effect of tropical climate on performance during repeated jump-and-reach tests.

AIM: The aim of the present study was to determine the effect of tropical climate (i.e., hot and humid) on performance during multiple jump-and-reach tests. METHODS: Fourteen male basketball players volunteered to perform 2 randomized series of jump-and-reach tests, which consisted of a jump-and-reach test every 15 sec for 5 min (21 jump-and-reach tests) in two thermal conditions: tropical (TR, 30.4 degrees C, 70% rh) and thermoneutral (TN, 23.1 degrees C, 53% rh). During each test, lactate concentration [La(-)], tympanic temperature (Tty), sweat rate (SR), heart rate (HR), and performance (height: H) were noted at rest, during exercise and recovery. Two hours of recovery separated the TN and TR tests. RESULTS: There were no significant differences in mean height, maximal height or the kinetics between TN and TR. Both conditions induced an increase in height over time (time effect: p<0.002). There were no significant differences in [La(-)] at rest or during exercise or recovery in the 2 conditions. Both conditions induced an increase in [La(-)] (time effect: p<0.002). There was a tendency toward a higher mean [La(-)] during TR than TN (situation effect, p<0.07). However, compared to resting values, [La(-)] values were significantly increased only in TR and not in TN. Tty, was significantly greater (p<0.001) at rest and during exercise and recovery in TR than in TN. SR and HR were also significantly greater at rest and during exercise and recovery in TR (p<0.001 for SR and HR). CONCLUSION: We conclude that tropical climate affects physiological responses without improving or decreasing performance during successive jump tests.

Adult↗
PubMed2002

Alactic anaerobic performance in subjects with sickle cell trait and hemoglobin AA.

The aim of the present study was to assess the performance of subjects with sickle cell trait (SCT) during brief and explosive exercise involving mainly anaerobic metabolism. One hundred and ninety-six black subjects underwent SCT screening, which revealed the presence of 16 subjects with SCT and 180 subjects with normal hemoglobin (HbAA). All subjects performed four tests: 1) a 100-m sprint, 2) a long-jump, 3) a Leger-Boucher shuttle test and 4) a jump-and-reach test. A control group (n = 18) selected from the 180 subjects with HbAA was matched according to the sex, age, weight and height of the SCT subjects (SCTs). The performances of the SCTs (n = 16) were compared with those of the control group. The performances were similar between the SCTs and control group for the sprint test, long-jump and the Leger-Boucher shuttle test. There was, however, a significant difference for the jump-and-reach test between the two groups: the SCTs (i. e., males plus females, and males and females considered separately) reached a significantly greater height (p < 0.05) than the matched subjects of the control group (63.7 +/- 3.6 vs. 58.6 +/- 3.1 cm, 72.3 +/- 3.9 vs. 67.1 +/- 2.4 cm and 52.7 +/- 3.2 vs. 45.3 +/- 2.0 cm for SCTs versus non-SCTs, for the group, the males and the females, respectively). The results of the present study suggest that the performance of brief and explosive exercise may be enhanced by HbS.

Adult↗
PubMed2002

Jump evaluation of elite volleyball players using two methods: jump power equations and force platform.

BACKGROUND: The aim of the present study was to determine the best jump power equation in the evaluation of elite volleyball players using both the force platform and peak power equations. METHODS: Nine elite volleyball players and nine sedentary subjects performed counter-movement jump tests on a force platform. RESULTS: Peak power and height were greater in the volleyball players than in the sedentary subjects, whatever the method used. The results demonstrated that the peak power values obtained on the force platform and those scored from the equations of Lewis, Harman and Sayers et al. were correlated when the whole sample was taken into account. However, a significant equation x level interaction (p<10(-4)) indicated different behaviour as a function of performance level. In sedentary subjects, peak power was significantly underestimated using the Lewis equation (943+/-162 W; p<10(-4)) and did not differ using both the Harman (3004+/-563 W) and Sayers (3400+/-604 W) equations when compared to the peak power noted with the force platform (3372+/-532 W). In contrast, in volleyball players, peak power was underestimated using the three equations (1246+/-78 W, p<10(-4); 4314+/-216 W, p<0.001; 4607+/-251, p<0.005; for the Lewis, Harman and Sayers equations, respectively, versus 5355+/-522 W for the force platform). CONCLUSIONS: The results of the present study demonstrate the difficulty in choosing the most relevant equation in the jump power calculation.

Adult↗
PubMed2001

Venous blood lactate increase after vertical jumping in volleyball athletes.

The aim of this study was to test the hypothesis that venous blood lactate concentrations ([La-]) would vary from the beginning of brief exercise. Maximal vertical jumping was used as a model of brief intense exercise. Eleven healthy male volleyball players, aged [mean (SE)] 18.5 (0.7) years, performed three exercise tests with different protocols, each separated by quiet seated recovery periods of 45 min. After the first test, consisting of a single maximal jump [lasting approximately equals 0.6 s for the pushing phase, and in which the subjects jumped 64 (2.2) cm], forearm venous [La-] increased significantly with respect to rest at 1 min (t1), 3 min (t3), and 5 min (t5) of recovery. The second test, comprising six maximal jumps, each separated by 20-s recovery periods, resulted in an unchanged [La-] with respect to the baseline value. After the third test [i.e., six consecutive maximal jumps that lasted a total of 7.36 (0.33) s], [La-] increased significantly at t3 and t5 with respect to the pre-test value (F= 10.3, P < 0.001). We conclude that a significant venous [La-] increase occurs after vertical jumping. This result may be explained by the activation of lactic anaerobic metabolism at the very onset of exercise, which participates in energy production and/or in the resynthesis of the phosphocreatine that was used during such brief exercise.

Adolescent↗
PubMed2001

Enhancing cycling performance using an eccentric chainring.

PURPOSE AND METHODS: This study was designed to compare the physiological responses and performance of well trained cyclists riding with two different chainring designs, round or eccentric, during a brief and intense cycling exercise: an "all-out" 1-km laboratory test. The eccentrically designed chainring was made of two crank arms sliding into each other, with the inside arm fixed on the center of the arm of a circular chainring and the outside arm sliding along the inside and revolving around an elliptical cam. This design increases crank arm length at the downstroke and decreases it during the upstroke, thus increasing and decreasing the torque. In terms of the chainring's revolution, the crank arm length at 0 degrees and 180 degrees is similar to the arm length of circular chainrings (175 mm). However, during the downstroke (0-180 degrees ), it increases to its maximum length of 200 mm at 90 degrees and then returns to its original length of 175 mm at 180 degrees. During the upstroke, it decreases to a minimum length of 150 mm at 270 degrees and then increases to 175 mm at 360 degrees. Eleven cyclists performed an all-out 1-km laboratory test using each chainring. The study was conducted over two consecutive weeks with the order of chainring use randomized. During all trials, ventilatory data were collected every minute using an automated breath-by-breath system. Heart rate was measured using a telemetry system. RESULTS: None of the cardiorespiratory variables showed significant differences between chainring trials. Performance, however, was significantly improved using the eccentric design (64.25 +/- 1.05 vs 69.08 +/- 1.38 s, P < 0.004, with the eccentric and the round design, respectively). CONCLUSION: We concluded that the eccentric chainring significantly improved the cycling performance during an all-out 1-km test. Further testing with indoor cycling specialists performing on a velodrome would be helpful to define the maximal possibilities of such a chainring.

Adolescent↗
PubMed2000

Insulin-like growth factor induces the survival and proliferation of myeloma cells through an interleukin-6-independent transduction pathway.

Multiple myeloma (MM) is a B-cell neoplasia that is associated with an increased level of bone resorption. One important mediator of bone remodelling, insulin-like growth factor (IGF-I), has been shown to stimulate the proliferation of human myeloma cells. However, the mechanisms of action of IGF-I in these cells have not been determined. Using interleukin (IL)-6-dependent myeloma cell lines, we show IGF-I to be as potent a survival and proliferation factor as IL-6. We demonstrated that IGF-I functions independently of the IL-6 transducer gp130 and that these two cytokines have additive effects. Moreover, inhibition of the IGF-I pathway did not modulate the proliferative effect of IL-6. Accordingly, we found that IL-6 and IGF-I activated distinct downstream signalling molecules: IL-6 activated STAT3 phosphorylation, whereas IGF-I treatment resulted in the phosphorylation of IRS-1. Interestingly, these signalling pathways appear to converge as both cytokines activated the ras/MAPK pathway. Thus, IGF-I acts as a potent survival and proliferation factor for myeloma cells by stimulating an IL-6-independent signalling cascade. These data, together with the finding that, in vivo, IGF-I is normally expressed in close proximity to myeloma cells within the bone matrix, strongly suggest a role for this cytokine in the pathophysiology of multiple myeloma.

Apoptosis↗
PubMed1992

The right to genetic information: some reflections on Dutch developments.

New developments in genetics are rapidly spreading over the Western World. The standards of clinical practice differ however according to local value- and health-care systems. In this article a short survey is given of Dutch developments in this field. An effort is made to explain the philosophical and ethical background of Dutch policy by concentrating on autonomy, responsibility and the right not to know.

Beneficence↗