PubMed Health⌕ Search

Biomedical subjects

J Van Hoecke

Publications and source records attributed to J Van Hoecke.

At least 37 records · Page 2Linked to original sources
PubMed1999

Isokinetic elbow flexion and coactivation following eccentric training.

The influence of an eccentric training on torque/angular velocity relationships and coactivation level during maximal voluntary isokinetic elbow flexion was examined. Seventeen subjects divided into two groups (Eccentric Group EG, n = 9 Control Group CG, n = 8) performed on an isokinetic dynamometer, before and after training, maximal isokinetic elbow flexions at eight angular velocities (from - 120 degrees s(-1) under eccentric conditions to 240 degrees s(-1) under concentric conditions), and held maximal and submaximal isometric actions. Under all conditions, the myoelectric activities (EMG) of the biceps and the triceps brachii muscles were recorded and quantified as the RMS value. Eccentric training of the EG consisted of 5x6 eccentric muscle actions at 100 and 120% of one maximal repetition (IRM) for 21 sessions and lasted 7 weeks. In the EG after training, torque was significantly increased at all angular velocities tested (ranging from 11.4% at 30 degrees (s-1) to 45.5% at - 120 degrees s(-1)) (p < 0.05). These changes were accompanied by an increase in the RMS activities of the BB muscle under eccentric conditions (from - 120 to - 30 degrees (s-1)) and at the highest concentric angular velocities (180 and 24 degrees s(-1)) (p < 0.05). The RMS activity of the TB muscle was not affected by the angular velocity in either group for all action modes. The influence of eccentric training on the torque gains under eccentric conditions and for the highest velocities was attributed essentially to neural adaptations.

Adult↗
PubMed1998

[Drawing movements and gravitational force: central or peripheral regulation?].

Drawing arm movements in four different directions: a) upward vertical (0 degree), b) upward oblique (45 degrees), c) downward vertical (180 degrees) and d) downward oblique (135 degrees), and at two different speeds, normal and fast, were executed by eight subjects. Movements of the arm were recorded using an optoelectronic (2 TV, 100 Hz) system which allowed the computer reconstruction of joint motion. Analyses focused upon pen kinematics in the frontal plane. Velocity profiles were unimodal for all conditions. The ratio of acceleration time to total movement time changed significantly as a function of the direction and the speed of the movement. Movement time and was not affected by movement direction and consequently changes in gravitational torques, for both speeds tested. Results from this study provide indirect evidence that the CNS executes movements by taking advantage of gravitational force.

Adult↗
PubMed1998

[Recovery of muscle contractility after a strength training session: mechanical, neurophysiologic and biochemical approach].

The purpose of this study was to observe the recovery of maximal strength immediately after a maximal eccentric strength training set. The trained female subjects (n = 8) performed 10 bouts of 10 maximal eccentric contractions of the quadriceps muscle. Each bout was separated by a 2 minutes rest period. Integrated electromyogram (iEMG) of the vastus medialis and the rectus femoris, and torque were measured before, just after, 24 and 48 hours after training session, at different knee angular velocity (-60, 0, 60, 120, and 240 degrees.s-1). Possible structural damage of the muscular cell were searched from the urinary concentration of some protein catabolism metabolites before (basal rate), 24 and 48 hours after the exercise. Maximal torque significantly fell for any angular velocity immediately after the training session: 13.6% at -60 degrees.s-1, 16.9% at 60 degrees.s-1, 7.5% at 120 degrees.s-1, 12.8% at 240 degrees.s-1 and 8.6% at 0 degree.s-1. This event was accompanied by an increase of the iEMG at the training angular speed, and by an increase of the metabolites concentration in a half part of the subjects. Strength developed during eccentric contraction showed the earliest recovery. And it even significantly overshot its initial level by 14.9% at 48 hours. A significant increase of the iEMG assessed at the eccentric velocity was then observed. In the same time, 3 of the 6 subjects showed an increase of their urinary concentration of the chosen metabolites in comparison with their initial values. This result may closely be connected with the supercompensation phenomenon, which first appears in the training mode. This phenomenon could partly be explained by the associated increase of the iEMG.

Adult↗
PubMed1997

Joined effects of pennation angle and tendon compliance on fibre length in isometric contractions: a simulation study.

The main purpose of this study was to investigate the joined behaviours of tendon and pennation angle during maximal isometric contractions. A musculotendon model of the human soleus muscle was simulated as a function of ankle joint position, which determines the soleus length. Analysis of the respective values of tendon length and pennation angle for various musculotendon lengths showed that the primary effects of tendon elasticity and pennation angle variation were to reduce the fibre length variations by absorption of the musculotendon lengthening. The efficiency of this reduction process was the highest at short soleus lengths and principally related to tendon length variations. Finally, it was suggested that the optimal solution for musculotendon actuators acting in high lengthening ranges were long tendon units and great pennation angles. The heuristic model used in this study highlighted the existence of some dynamic phenomena inside the actuator. However, it did not pretend to represent the overall complexity of the mechanical interactions between the different elements composing the soleus architecture.

Ankle Joint↗
PubMed1997

Concentric and/or eccentric training-induced alterations in shoulder flexor and extensor strength.

To examine the effect of specific concentric and eccentric training on muscular strength following an initial standardized period of excessive training, shoulder extensors and flexors were tested. The shoulder is a joint particularly susceptible to injury and requires a specific strength training program. For a period of 12 weeks, subjects performed training, including concentric and eccentric actions. Thereafter, they were divided into three groups that performed specific 12-week programs, including either concentric (C-E/C), eccentric (C-E/E), or a combination of both concentric and eccentric exercises (C-E/C-E). Following the initial period of training, significant increases (p < 0.05) in performance were observed for all experimental groups. The C-E/C group showed significant increases (p < 0.05) in performance after 24 weeks of training, especially at high concentric angular velocities. However, the C-E/E group showed significant increases (p < 0.05) only in their eccentric moments. No significant differences were noted for the C-E/C-E group. These findings seem to partly confirm the mode-specificity principle, as only the concentric-specific training program improved concentric and eccentric strength. Moreover, the velocity-specificity principle was strongly supported.

Adolescent↗
PubMed1997

Circadian rhythm in the torque developed by elbow flexors during isometric contraction. Effect of sampling schedules.

Time-dependent changes in elbow flexion torque have been documented according to two different sampling schedules. Seven physical education students took part in the first series of experiments, and 7 other similar subjects in the second. In both sets of experiments, the subjects performed isometric contractions: maximal and submaximal at 90 degrees in the first experiments and maximal at different angular positions in the second. After a 30-minute rest period, the torque developed was measured at 00:00, 06:00, 09:00, 12:00, 15:00, 18:00, and 21:00 h on the day of the experiment. These subjects remained in the laboratory for 24 h. In the second series of experiments, the torque developed was measured at 01:00, 05:00, 09:00, 13:00, 17:00, and 21:00 h over the subsequent 6 days with only one test session per day. In this case, there was an interval of 20 h between two successive test sessions. In the first experiment, a significant time-of-day effect was observed for the torque of the elbow flexors under isometric conditions with an acrophase at 17:58 h. The 24 h normalized mean score was 92.85% with an amplitude of 7.63% of the daily mean. In the second series of experiments, there was evidence of a circadian rhythm in the torque developed by the elbow flexors at every angle position, especially at 90 degrees, the angle investigated in the first set of experiments. The peak torque was calculated to have occurred at 17:55 h. The amplitude of the rhythm was equal to 6.99% of the daily mean. There were no statistically significant differences in the characteristics of the circadian rhythm observed between the two experimental designs. We concluded that an experiment extending over several days could be employed to evaluate circadian rhythms in muscular activity reliably.

Adult↗
PubMed1996

Viscosity of the elbow flexor muscles during maximal eccentric and concentric actions.

The aim of the present study was to estimate the damping coefficient (B factor) of the elbow flexor muscles during both eccentric and concentric muscle actions. We used a muscle model consisting of a viscous damper associated in parallel with a contractile component, both in series with an elastic component. The viscous damper allowed the concentric loss and the eccentric gain of force to be modelled. Eight volunteer subjects performed maximal eccentric and concentric elbow movements on an isokinetic dynamometer at angular velocities of 0.52, 1.04 and 2.09 rad*s(-1). Torques at an elbow joint angle of 90 degrees were recorded. Electromyogram (EMG) signals from the belly of the right elbow flexor and from the long head of the triceps brachia muscles were recorded using two pairs of bipolar surface electrodes. The root mean square (rms) of the EMG was determined. Eccentric and concentric rms were not significantly different (P >0.05). The B factor was higher in the concentric than in the eccentric conditions (P <0.05), and, whatever the muscle action type it decreased as the velocity increased. These results indicated that the concentric loss and the eccentric gain of force were attributable to the behaviour of the contractile machinery. Furthermore, whatever the exact cause of loss and gain of tension, our study showed that the total effect can be modelled by the viscous damper of a three-component muscle model.

Adult↗
PubMed1996

Simulation of in situ soleus isometric force output as a function of neural excitation.

The purpose of this study was to investigate the behaviour of the human soleus muscle during isometric contraction. A model taking into account the musculoskeletal geometry, the musculotendon architecture and the neural excitation input has been developed. The neural excitation input was simulated using a recruitment and firing rate organisation model. The musculotendon actuator was modelled as a tendon inserted in series with fibres defined by a contractile component in parallel with an elastic component. At maximal neural excitation, the model highlighted the functional significance of tendon stiffness and pennation angle. These architectural parameters tended to increase the operative ankle joint angle range of the soleus actuator, either to the maximal plantarflexion positions for the pennation angle or to the maximal dorsiflexion positions for tendon elasticity. When the model was simulated under various neural excitation levels, it predicted a displacement of the soleus fibre optimal length towards the soleus long length (maximal dorsiflexion position) with increasing neural excitation. The study concluded that the effect of muscular architecture should be taken into account to analyse the effect of neural excitation level on isometric force output.

Ankle Joint↗
PubMed1996

Diurnal rhythm of the muscular performance of elbow flexors during isometric contractions.

The influence of time of day on elbow flexion torque was studied. Thirteen physical education students, 7 males and 6 females, made maximal and submaximal isometric contractions at 90 degrees of elbow flexors using a dynamometer. The torque developed was measured on each contraction. The myoelectric activity of the biceps muscle was also measured at the same time by surface electromyography (EMG) and quantified from the root mean square (RMS) activity. Torque and surface EMGs were measured at 6:00, 9:00, 12:00, 15:00, 18:00, 21:00, and 24:00 h over the same day. Oral temperature before each test session was measured on each occasion after a 30-min rest period. We observed a diurnal rhythm in elbow flexor torque with an acrophase at 18:00 h and a bathyphase at 6:00 h, in phase with the diurnal rhythm in oral temperature. However, the diurnal rhythm of temperature did not appear to have any influence on the torque. Links between neuromuscular efficiency and RMS/torque ratio were evaluated by measuring muscle activity along with torque. We also assessed variations in the level of maximal activity of the muscle under maximal voluntary contraction. Neuromuscular efficiency fluctuated during the day, with maximal and minimal efficiency at 18:00 h and 9:00 h, respectively, whereas activation level was maximal at 18:00 h and minimal at 9:00 h. The diurnal rhythm of torque was accounted for by variations in both central nervous system command and the contractile state of the muscle.

Adult↗
PubMed1996

[Recruitment of the bi-articular gastrocnemius muscles during maximal isometric contractions in humans].

The main purpose of this study was to investigate the maximal isometric plantarflexion moment as a function of the triceps surae's length. As the gastrocnemius are bi-articular actuators, their respective lengths were modified by variations of the ankle and knee joints angles. The mechanical results agreed ones previously published in the literature. The maximal and minimal isometric moments were attained at maximal lengthening and shortening of the gastrocnemius respectively. The gastrocnemius electromyographic (EMG) activities showed paradoxal results. Their EMG activities decreased with their lengthening when this was induced by ankle joint angle variations. Inversely, their EMG activities increased with their lengthening when this was induced by knee joint angle variations. These results allowed the authors to hypothesize the existence of specific recruitment of neuro-muscular compartments of the gastrocnemius with knee extension.

Ankle Joint↗
PubMed1993

Influence of arterial blood pressure and aldosterone on left ventricular hypertrophy in moderate essential hypertension.

In a group of 36 untreated patients with mild-to-moderate essential hypertension (office systolic blood pressure [SBP] 160 +/- 3.4 mm Hg, office diastolic blood pressure [DBP], 102 +/- 1.5 mm Hg), 24-hour ambulatory blood pressure monitoring, and determination of left ventricular (LV) mass index according to the formula of Devereux were performed. After an overnight fast, blood samples were taken for the determination of serum aldosterone levels and plasma renin activity. Urinary catecholamine concentrations were assayed from 24-hour urine collections. Left ventricular mass index (143.7 +/- 8 g/m2) did not correlate significantly with either office SBP or office DBP. The correlation of LV mass index with mean 24-hour SBP (145 +/- 3 mm Hg) was statistically significant: r = 0.395, p = 0.026. However, the best correlation was obtained with mean 24-hour DBP (90 +/- 3 mm Hg) with r = 0.499 (p = 0.004). Urinary catecholamine levels did not correlate with LV mass index. In addition, LV mass index correlated significantly with plasma renin activity (r = 0.346, p = 0.050) and serum aldosterone levels (r = 0.559, p = 0.0009). There was a strongly significant correlation between LV mass index and serum aldosterone levels even after adjustment for mean 24-hour SBP (r = 0.496, p = 0.005) and DBP (r = 0.514, p = 0.004). These results demonstrate that ambulatory blood pressure determinations but not office blood pressure parameters correlate well with left ventricular hypertrophy in essential hypertension. Nonhemodynamic factors are important determinants of left ventricular mass as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Biomechanical study of the final push-pull in archery.

The purpose of this study was to analyse archery performance among eight archers of different abilities by means of displacement pull-hand measurements during the final push-pull phase of the shoot. The archers showed an irregular displacement negatively related to their technical level. Displacement signal analysis showed high power levels in both the 0-5 Hz and 8-12 Hz ranges. The latter peak corresponds to electromyographic tremor observed during a prolonged push-pull effort. The results are discussed in relation to some potentially helpful training procedures such as biofeedback and strength conditioning.

Adult↗
PubMed1992

Myoelectrical and metabolic changes in muscle fatigue.

In isometric contraction-induced fatigue force loss has been related to mostly myoelectrical or intramuscular events. However, some factors potentially involved may interfere at more than one site in these events and it has proven difficult to distinguish between those influences. The study of the relationships between force generating capacity, the metabolic state of a muscle and its myoelectrical properties may therefore help broaden our understanding of the fatigue process. In order to investigate these relationships, we have evaluated changes in force-generating capacity, NMR-determined metabolic variables, and myoelectrical activity, as measured from surface EMG, simultaneously in brachial biceps muscle of healthy subjects, during different types of fatiguing isometric exercise and during recovery. Factors studied include intramuscular pH, inorganic phosphate and its diprotonated form concentrations, root-mean square and mean power frequency of the EMG power spectrum, and neuromuscular efficiency index. Results show that different mechanisms are likely to contribute to force loss in fatiguing muscle and during different phases of recovery from fatigue. Indeed, relationships between variables from the three groups differed according to exercise protocol as well as in fatiguing and recovering muscle.

Electromyography↗
PubMed1991

Influence of the arterial blood pressure and nonhemodynamic factors on left ventricular hypertrophy in moderate essential hypertension.

In a group of 36 untreated patients with mild to moderate essential hypertension (office systolic and diastolic blood pressures (BPs) 160 +/- 3.4 and 102 +/- 1.5 mm Hg, respectively), a 24-hour ambulatory BP monitoring and determination of left ventricular (LV) mass index according to the formula of Devereux were performed. After an overnight fast, blood samples were taken for the determination of serum aldosterone, plasma renin activity and serum parathyroid hormone. Urinary catecholamines were sampled for 24 hours. LV mass index (143.7 +/- 8 g/m2) did not correlate significantly either with office systolic or diastolic BP. The correlation of LV mass index with mean 24-hour systolic BP (145 +/- 3 mm Hg) was statistically significant: r = 0.395, p = 0.026. However, the best correlation was obtained with mean 24-hour diastolic BP (90 +/- 3 mm Hg) with r = 0.500 (p = 0.004). Urinary catecholamines were not correlated with LV mass index. LV mass index correlated significantly with plasma renin activity (r = 0.346, p = 0.050), and aldosterone (r = 0.559, p = 0.001). There was a very significant correlation between LV mass index and parathyroid hormone (r = 0.719, p = 0.00001) even after adjustment for mean 24-hour systolic and diastolic BPs. These results clearly demonstrate that ambulatory BP determinants but not office BP parameters are well correlated with LV hypertrophy in essential hypertension. Nonhemodynamic factors are important determinants of LV mass as well. Besides the renin-angiotensin-aldosterone system, parathyroid hormone appears to play an important role in cardiac hypertrophy.

Adult↗
PubMed1991

EMG spectral shift- and 31P-NMR-determined intracellular pH in fatigued human biceps brachii muscle.

We have simultaneously recorded human biceps brachii intracellular pH, estimated by 31P-NMR, and EMG spectral shift, during isometric contraction and recovery in six subjects. This method allows us to concurrently study several components of muscle fatigue. The results show a clear dissociation between the recovery of intracellular pH, force-generating capacity, and the shift to low frequency of the EMG power spectrum induced by fatiguing exercise.

Electromyography↗
PubMed1990

Changes in elastic characteristics of human muscle induced by eccentric exercise.

The effect of an eccentric strength training programme on the muscular series elastic component (SEC) was studied on the flexors of the human elbow. The characteristics of the SEC were determined using an in situ technique derived from methods commonly used on isolated muscles. The results were expressed in terms of compliance-force and tension-extension relationships. These relationships indicate a sharp increase in compliance when tension decreases. Furthermore, for a given value of tension, the SEC compliance of the trained muscles is found to be lower than that of the untrained muscles. These results are discussed in relation to the active and passive parts of the SEC.

Adult↗