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«BOOK OF ABSTRACTS Edited by: Loland, S., Bø, K., Fasting, K., Hallén, J., Ommundsen, Y., Roberts, G., Tsolakidis, E. Hosted by: The Norwegian ...»

-- [ Page 45 ] --
Introduction: Aging induces alterations of sympathoadrenergic system (Zouhal et al. 2008). It could be explained by an increase in the sympathetic nervous activity with advancing age and/or by a compensatory mechanism related to the fall of the organization sensitivity to sympathoadrenal stimulation (Mazzeo et al. 1997). It is well known that endurance training induces an increase in adrenal gland (AG) and adrenal medulla (AM) volume in young rats (Stallknecht et al. 1990). Previous internal study showed that high frequency of endurance training is more efficient in young rat (Poulain et al. 2008). In old rat, the endurance training frequency efficient to modify the volume of AG and AM remained to be clarified. The purpose of the present study was to compare the effects of two endurance training programs with different frequencies (endurance training session per week) on AG and AM in old rats.

–  –  –

Methods 16 old Wistar rats were randomly assigned to one of the three groups: untrained (UT), trained 2 times per week (T2) and trained 5 times per week (T5). Training consisted in 8 weeks of endurance training (1h/day on a treadmill at a speed of 20 m/min up a 10 degrees inclineon). All rats were weighted at the beginning and the end of the protocol. 24h after the last training session, animals were killed and AG were removed, weighted and frozen for subsequent analysis. The method of volume determination is based on the measurement of the elliptical surface of every cut of 10μm thicknesses spaced out by 99 cuts. Formula used was vol (mm3) = Σ each surface x 0,1. The ImageJ software calculates the surface from the number of present pixels. The surface delimitation is determined manually. The results are given as mean ± SD.

Results: T2 (489 ± 46 g) and T5 (495 ± 35 g) had not significantly different of body mass to UT (485 ± 6 g) at the end of the endurance training program. The volume of AG is not significantly different between the three groups. However, T2 and T5 have a lower volume of MS (1.53 ± 0.52 mm3 and 1.88 ± 0.43 mm3, respectively) than UT (2.48 ± 0.36 mm3). Also, AM/AG volume is higher in sedentary rats (0.112 ± 0.008) compared to T2 (0.088 ± 0.020) and T5 (0.089 ± 0.031).

Discussion Amazingly, in older rat, it seems that two endurance training session per week induce a decrease in AM volume without changing the AG volume. This data shows an opposite effect of endurance training between young and old rats. This could be explained by an initial higher volume of AM in old untrained rat and the endurance training could have a beneficial effect at this level by reducing. So, training seems to give « a second youth » to the older rats at AM area. In conclusion, endurance training one hour per day realized two times per week seems sufficient to induce such adjustments in the AM of older rats.

References Mazzeo et al. J. Appl. Physiol. 82:1869-1874, 1997 Poulain et al. 15th World congress of Sports Medicine, Barcelona 2008 Stallknecht et al. Am. J. Physiol. 259 R998-R1003, 1990 Zouhal et al. Sports Med. 38(5):1, 2008

AGE-SPECIFIC AND TRAINING-INDUCED MUSCLE ACTIVATION PROFILES DURING REPETITIVE HOPPING

HOFFRÉN, M., ISHIKAWA, M., KOMI, P.V.

UNIVERSITY OF JYVÄSKYLÄ

Neural activation strategies play an important role during the dynamic movements by controlling the fascicle behavior and therefore also the fascicle-tendon interaction and movement efficacy. There are indications that the muscle activation profiles (1) and fascicle-tendon interactions (2) are age-specific. This information has been obtained during dynamic movements performed by young and older individuals using the same exercise intensities in absolute scale. This may not be a preferred protocol since activation strategies are modified by the movement intensity (3). The purpose of the present study was to investigate whether the age-specific muscle activation profiles exist in repetitive hopping exercise and whether the hopping training modifies the activation profiles in elderly. The exercise intensities for younger and elderly subjects were adjusted according to their individual maximal hopping performance.

12 elderly and 8 young subjects performed repetitive bilateral hopping with different intensities (50%, 65%, 75%, 90% and maximal) of the maximal vertical ground reaction force. EMG activation of the soleus (SOL), gastrocnemius medialis (GM), gastrocnemius lateralis (GL) and tibialis anterior (TA) muscles were investigated during hopping. RMS values of EMG were calculated for the preactivation (100ms prior to contact), braking and push-off phases. The measurements were repeated for the Elderly after 2 weeks and 12 weeks of hopping training that was performed 3 times per week.

When the ratio preactivation to braking phase activation (pre/brak-ratio) was calculated, Elderly showed signicantly higher values in SOL, GM and TA muscles than Young. The trend for the same was also seen in GL (p=0.053). This ratio did not change in Elderly during hopping training. However, when another EMG ratio (braking to push off) showed originally lower values among Elderly, the specific hopping training increased this ratio especially in high exercise intensities (90% and max hopping) in SOL, GM and GL muscles.

It is likely that age-specific muscle activation profiles exist in repetitive hopping exercise. As compared to Young, Elderly have high preactivation of the agonist muscles, then less activation in the braking phase and increasing activation towards the end of push-off phase.





This activation in elderly may affect the stiffness regulation and utilization of tendinous tissue elasticity. However, the activation strategies are trainable also in elderly since the short-term hopping training shifted the activation from the push-off phase towards the braking phase resembling the activation of young individuals.

References

1. Hoffrén et al. (2007) J Appl Physiol. 103: 1276-1283

2. Mian et al. (2007) Acta Physiol. 189: 57-65

3. Sousa et al. (2007) J Appl Physiol. 102: 382-389

CARDIORESPIRATORY RESPONSES DURING SIX MINUTES WALKING TESTS IN TRAINED AND UNTRAINED ELDERLY

SUBJECTS

YÁZIGI, F., REIS, J., ALVES, F., ARMADA-DA-SILVA, P.

FACULTY OF HUMAN KINETICS

Although several studies used the Six Minutes Walking Test (6MWT) in order to evaluate the functional capacity of special populations, there is a lack of information regarding the cardiorespiratory parameters obtained during this test in healthy elderly subjects, as well as its sensitivity to the effect of exercise training. The purpose of this study is to characterize the cardiorespiratory responses during the 6MWT by comparison of two groups of elderly subjects (trained and untrained). Methods: Twenty eight subjects divided into two groups:

trained (T) (n=20; age: 73.1 ± 6.7 yrs (SD); height: 1.61 ± 0.1 m; weight: 68.3 ± 11. kg) and untrained (UT) (n=8; age: 69.0 ± 7.3 yrs (SD);

height: 1.60 ± 0.1 m; weight: 73.2 ± 9.0 kg) performed the 6MWT with cardiorespiratory responses assessed by a portable gas analyzer (Cosmed K4b2). Subjects were instructed to walk as fast as possible and the distance (d) and gait speed (v) were recorded. The maximal oxygen uptake ( O2) and heart rate (HR) achieved were calculated as the average of the first 3 minutes ( O2_3’) and the last 3 min of the test ( O2_6’). The relation between the HR obtained by each subject and their theorical maximal heart rate according to Tanaka’s formula was established (%HR). The training process consisted in 8-months multicomponent training, developed according the ACSM guidelines.

Independent and paired T-tests were used to compare means between and within groups, respectively. Pearson’s product moment

14 ANNUAL CONGRESS OF THE EUROPEAN COLLEGE OF SPORT SCIENCE

TH Wednesday, June 24th, 2009 coefficient was used to correlate variables. Results: Trained group presented higher d (T = 660 ± 83 m; UT = 520 ± 82 m; p = 0.00), v (T=

1.83 ± 0.2 ms-1; UT = 1.44 ± 0.2 ms-1; p = 0.00), O2 (T = 19.9 ± 8.0 ml min-1kg-1; UT = 14.3 ± 4.3 ml min-1kg-1; p = 0.03) and %HR (T = 83 ± 11%; UG= 70 ± 14%; p = 0.01). The difference between O2_6’ and O2_3’ was 2.6± 2 ml min-1kg-1 in T (p= 0.000) and 0.4± 0.9 ml minkg-1 in UT (p= 0.24) also suggesting higher exercise relative intensity in the former group. Also, significant correlations were found between d and O2 (r = 0.68; p = 0.00) and between %HR and O2 (0.67; p = 0.00). The results demonstrate that 6MWT is a valid instrument to assess aerobic capacity in elderly individuals, confirming the higher aerobic performance in trained individuals. The T group increased the oxygen consumption until the end of test either due to increased walking speed or due to higher intensity exercise and occurrence of a slow component of O2 consumption kinetics. No such phenomenon was observed in the UT group.

14:00 - 15:30 Oral presentations OP-BM04 Biomechanics 4

CORTICOSPINAL EXCITABILITY DURING CONCENTRIC AND ECCENTRIC MAXIMAL VOLUNTARY CONTRACTION

DUCLAY, J., PASQUET, B., KLASS, M., MARTIN, A., DUCHATEAU, J.

UNIVERSITÉ LIBRE DE BRUXELLES

Introduction: During submaximal plantar flexion, it has been reported that the excitability of the spinal and and corticospinal pathway, evaluated respectively by the H-reflex and by motor evoked potentials (MEP) elicited by transcranial magnetic stimulation, was lower during eccentric compared with concentric contraction (Sekiguchi et al., 2003). In a previous study, we showed that the depression of the H-reflex amplitude during eccentric compared with concentric maximal voluntary contractions (MVC) was only observed in the soleus (SOL) muscle while no muscle contraction type effect was obtained for the medial gastrocnemius (MG) H-reflex (Duclay et al., 2008). Our findings suggested that, during eccentric MVC, the neural control mainly act at spinal level (Duclay and Martin 2005). The aim of the current study was therefore to investigate cortical and spinal neural mechanisms involved in the neural modulations observed during eccentric MVC in two muscles (SOL and MG) which could be differently affected by peripheral inhibitory mechanisms.

Methods: Experiments were performed on 9 healthy men. Maximal H-reflexes, M-waves and MEP were evoked in both SOL and MG at an ankle angle of 90° during concentric and eccentric MVC (i.e., Hsup, Msup and MEP, respectively). The MEP / Msup and Hsup / Msup were calculated to investigate the corticospinal and spinal excitability.

Results: During MVC, both SOL Hsup / Msup and MEP /Msup ratios were lower during eccentric contraction (P0.01) as compared with concentric contraction (0.39 ± 0.04 vs. 0.54 ± 0.04 and 0.13 ± 0.01 vs. 0.17 ± 0.01 respectively) while corresponding MG ratios were not affected by the muscle contraction type (P0.05). To evaluate the specific neural control at corticospinal and spinal level during eccentric MVC as compared with concentric MVC, differences between concentric and eccentric values of the amplitude for MEP / Msup (ΔMEP) and Hsup/Msup (ΔH) were fitted into linear regression. For the SOL, significant correlation was observed between ΔMEP and ΔH (P0.05). When ΔH was increased, a decrease of ΔMEP was obtained.

Discussion: The SOL results indicate that the excitability of the corticospinal pathway is reduced during eccentric compared with concentric MVC. The relation between ΔMEP and ΔH, observed for the SOL, suggest that, during eccentric MVC, cortical excitability was increased in order to compensate for spinal inhibition. Despite this increase, the MEP / Msup ratio was lower during eccentric MVC, suggesting that the corticospinal pathway seems to be mainly modulated at spinal level. In the same way, when the amount of inhibition was less at spinal level (i.e. MG’s data) (Duclay et al 2008), the corticospinal excitability was similar during eccentric compared with concentric MVC.

References Duclay J, Martin A (2005). J Neurophysiol 94: 3555-3562 Duclay J, Robbe A, Pousson M, Martin A (2008). J Electromyogr Kinesiol. Jun 12.

Sekiguchi H, Nakazawa K, Suzuki S (2003). Brain Res 977: 169–179

ELITE CROSS-COUNTRY SKIERS’ ADAPTATIONS OF THE DIAGONAL STRIDE TECHNIQUE AT DIFFERENT INCLINATIONS

GOEPFERT, C., HOLMBERG, H.C.,4, MUELLER, E., LINDINGER, ST.,2

UNIVERSITY OF SALZBURG, AUSTRIA

3. Swedish Winter Sports Centre, Department of Health Sciences, Mid Sweden University, Östersund

4. Swedish Olympic Committee, Stockholm, Sweden Introduction: Despite the equal relevance of classic and freestyle in modern cross-country skiing, the main focus of biomechanical studies has mainly been on the latter technique. Diagonal stride [DIA] as a main classical technique has further developed over the last 20 years.

There is still a lack of biomechanical data describing DIA and adaptations to different inclinations. A previous study showed that skiers increased cycle rate rather than cycle length as the strategy to adapt to increasing inclinations (Bilodeau et al. 1992). However, no kinetic or joint kinematic data were presented. The aim of the present study was to identify kinetic and kinematic adaptations in DIA at different inclinations.

Methods: Twelve elite XC skiers (Swedish National Team; VO2max-DIA: 72.3 ± 3.8 ml·kg-1·min-1) performed DIA roller skiing at treadmill inclinations of 3°, 6° and 9° at 11 km·h-1 for biomechanical analyses. Leg and arm joint angles (goniometers), pole force (strain gauge), both at 2000 Hz, and plantar force (Pedar Mobile) at 100 Hz were recorded. Repeated measures ANOVA were calculated in order to examine the biomechanical differences between the named inclinations. The statistical level of significance was set at P0.05.



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