Biomedical subjects

J Avela

Publications and source records attributed to J Avela.

At least 19 recordsLinked to original sources

PubMed2006

Changes in the soleus muscle architecture after exhausting stretch-shortening cycle exercise in humans.

This study focused on the architectural changes in the muscle-tendon complex during the immediate and secondary (delayed) reductions of performance (bimodal recovery) caused by an exhaustive rebound type stretch-shortening cycle (SSC) exercise. The isometric plantar flexor torque during maximum voluntary contraction (MVC) was measured together with recording of electromyography (EMG) and ultrasonography from the soleus muscle before (BEF), after (AFT), 2 h (2H), 2 and 8 days (2D, 8D) after the SSC exercise (n=8). The performance variables (MVC torque and EMG activation) followed the bimodal recovery patterns. This was not the case in the changes of the fascicle length and muscle thickness. The relative torque changes in MVC correlated positively (R=0.78, P=0.02) to the corresponding averaged EMG changes between BEF and 2H (BEF-->2H); the significance disappeared in the comparison between 2H and 2D (2H-->2D), during which period MVC showed a secondary reduction. The relative torque changes in MVC showed no correlation with the changes in muscle thickness between BEF-2H. However, this correlation between 2H-2D was negative (R=-0.85, P<0.01). The fascicle shortening/average EMG ratio in MVC increased at 2H, and then decreased more at 2D than 2H (P<0.05). Thus, the secondary performance decline was not related to the corresponding EMG reduction but to the increased muscle thickness, which peaked at 2D. The results suggest clearly that the secondary decline in MVC could be related to the increase in muscle volume.

Adult↗

PubMed2005

Effects of power training on muscle structure and neuromuscular performance.

The present study examines changes in muscle structure and neuromuscular performance induced by 15 weeks of power training with explosive muscle actions. Twenty-three subjects, including 10 controls, volunteered for the study. Muscle biopsies were obtained from the gastrocnemius muscle before and after the training period, while maximal voluntary isometric contractions (MVC) and drop jump tests were performed once every fifth week. No statistically significant improvements in MVC of the knee extensor (KE) and plantarflexor muscles were observed during the training period. However, the maximal rate of force development (RFD) of KE increased from 18,836+/-4282 to 25,443+/-8897 N (P<0.05) during the first 10 weeks of training. In addition, vertical jump height (vertical rise of the center of body mass) in the drop jump test increased significantly (P<0.01). Simultaneously, explosive force production of KE muscles measured as knee moment and power increased significantly; however, there was no significant change (P>0.05) in muscle activity (electromyography) of KE. The mean percentage for myosin heavy chain and titin isoforms, muscle fiber-type distributions and areas were unchanged. The enhanced performance in jumping as a result of power training can be explained, in part, by some modification in the joint control strategy and/or increased RFD capabilities of the KE.

Adult↗

PubMed2003

Voluntary activation and mechanical performance of human triceps surae muscle after exhaustive stretch-shortening cycle jumping exercise.

The purpose of this study was to examine neuromuscular factors that may contribute to post exercise force loss and subsequent recovery after exhaustive stretch-shortening cycle (SSC) exercise. Six subjects were fatigued on a sledge apparatus by 100 maximal rebound jumps followed by continuous submaximal jumping until complete exhaustion. Exercise-induced changes in neuromuscular performance were followed up to 7 days post exercise. The total number of jumps in the SSC exercise ranged from 336 to 1392. The SSC exercise induced a significant immediate plantarflexion torque decline of 29, 38 and 44% ( P<0.05) in maximal voluntary contraction and evoked maximal twitch and low-frequency (LF) stimulation, respectively. The higher the number of jumps in the SSC exercise the larger was the post exercise reduction in voluntary activation as well as in contractile force ( r=-0.94, P<0.01, in both). Furthermore, a higher number of jumps augmented a delayed force recovery and late decline in stretch reflex EMG response ( r=-0.94, P<0.01). Clear differences were found in central and peripheral adaptation to the exhaustive SSC exercise between the subjects. The magnitude of post exercise contractile and activation failure as well as the delayed recovery of neuromuscular performance may have been augmented in some subjects due to their high number of jumps in the exercise.

Adaptation, Physiological↗

PubMed2003

Effects of power training on mechanical efficiency in jumping.

The present study investigates the effects of power training on mechanical efficiency (ME) in jumping. Twenty-three subjects, including ten controls, volunteered for the study. The experimental group trained twice a week for 15 weeks performing various jumping exercises such as drop jumps, hurdle jumps, hopping and bouncing. In the maximal jumping test, the take-off velocity increased from 2.56 (0.24) m.s(-1) to 2.77 (0.18) m.s(-1) ( P<0.05). In the submaximal jumping of 50% of the maximum, energy expenditure decreased from 660 (110) to 502 (68) J.kg(-1).min(-1) ( P<0.001) while, simultaneously, ME increased from 37.2 (8.4)% to 47.4 (8.2)% ( P<0.001). Some muscle enzyme activities of the gastrocnemius muscle increased during the training period: citrate synthase from 35 (8) to 39 (7) micromol.g(-1) dry mass.min(-1) ( P<0.05) and beta-hydroxyacyl CoA dehydrogenase from 21 (4) to 23 (5) micromol.g(-1) dry mass.min(-1) ( P<0.05), whereas no significant changes were observed in phosphofructokinase and lactate dehydrogenase. In the control group, no changes in ME or in enzyme activities were observed. In conclusion, the enhanced performance capability of 8% in maximal jumping as a result of power training was characterized by decreased energy expenditure of 24%. Thus, the increased neuromuscular performance, joint control strategy, and intermuscular coordination (primary factors), together with improved aerobic capacity (secondary factor), may result in reduced oxygen demands and increased ME.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2003

Effects of long- and short-term fatiguing stretch-shortening cycle exercises on reflex EMG and force of the tendon-muscle complex.

This study examined the fatigue effects of stretch-shortening cycle exercises of different intensity and duration on stretch reflex EMG and mechanical responses of the triceps surae muscle. Twelve subjects performed either a 10-km run ( n=6) or short but exhaustive rebound exercise on a sledge apparatus ( n=6). Passive reflex tests (mechanically induced ankle dorsiflexions) were examined before, after as well as 2 h, 2 and 7 days after exercise. Mechanical reflex responses were recorded from the ergometer torque signal. An acute contractile failure was observed as large reductions in twitch responses, especially in the sledge subgroup who showed high post-exercise peak blood lactate and an increased EMG/torque ratio. Independently of the exercise, the delayed fatigue analysis revealed strong relationships between the reflex-induced EMG and mechanical changes. In addition to muscle damage, these results may be explained by inhibitory effects via the sensitisation of small muscle afferents particularly during the exercise-induced delayed recovery process.

Adolescent↗

PubMed2003

Neuromuscular behaviour of the triceps surae muscle-tendon complex during running and jumping.

The present study examined the behaviour of the Achilles tendon (AT) - triceps surae (TS) muscle complex during running and long jump take-off. High AT forces were measured in the push-off phase in running even with very low EMG activity. In the long jump, high rate of stiffness development was a characteristic of the braking phase of the jump. The results suggest that high and well-coordinated activation patterns of the leg extensor muscles during the preactivation and eccentric phases together with high stretching velocities of muscle-tendon complex provide basis for appropriate tendomuscular stiffness. This together with high force at the end of the eccentric phase enables an effective push-off (concentric) phase.

Achilles Tendon↗

PubMed2003

Maximal but not submaximal performance is reduced by constant-speed 10-km run.

AIM: Effects of endurance exercise on running economy, mechanics, force generating capacity and their interactions were examined. During the exercise, metabolic, kinetic and kinematic variables were recorded to find out adaptive mechanisms in the course of the fatiguing run. In addition, before and after it maximal force and power production was tested. METHODS EXPERIMENTAL DESIGN: comparative. SETTING: University. PARTICIPANTS AND INTERVENTION: 7 men unaccustomed to endurance training run 10 km at individually chosen constant speed (3.5+/-0.5 m x s(-1)) on an indoor track. MEASURES: 3-D ground reaction forces, electromyographic (EMG) activities from 7 leg muscles, pulmonary ventilation, gas exchange, heart rate and movement kinematics were measured during the run. Blood lactate and serum creatine kinase activity were determined. Maximal voluntary contraction (MVC) with superimposed double twitch (DT), and passive DT tests in plantarflexor muscles were performed before and after the 10 km run. Changes in 20 m sprint performance were evaluated in before-after comparison. RESULTS: The 10 km run caused significant reductions in maximal running speed (8.2 vs 7.6 m x s(-1), p<0.05), in MVC (1216 vs. 984 N, p<0.05), and in passive DT (271 vs 211 N, p<0.05). During the submaximal run, however, the subjects were able to maintain relatively constant oxygen consumption and running kinematics. Greatest changes in EMG activity and kinetics were seen during the first 2 km. CONCLUSION: After initial adjustment, the runners are able to maintain submaximal running speed with very little changes in running economy, kinetics and kinematics. However, fatigue-induced impairment in the force generating capacity of the contractile component can be revealed by tests measuring maximum performance.

Adult↗

PubMed2002

Exhausting stretch-shortening cycle (SSC) exercise causes greater impairment in SSC performance than in pure concentric performance.

The purpose of the present study was to investigate the fatigue effect of repeated exhaustive stretch-shortening cycle (SSC) exercise on concentric muscle function. Ten healthy male subjects performed SSC exercise [92 (30) jumps] on a special sledge apparatus. Exhaustion occurred on average within 3 min. A squat jump (SJ) test utilizing a concentric-only action was performed immediately before and after the SSC exercise, and then 10 min, 20 min, 2 days and 4 days later. In addition, a drop jump (DJ) test using an SSC was also performed immediately before and 20 min after the SSC exercise, and 2 days and 4 days later. During jump tests, lower limb joint moment, power, and work contributions were analyzed by using the kinetic and kinematic data. The fatigue exercise was characterized by a relatively high blood lactate concentration [7.2 (0.8) mmol x l(-1)] and a 2-day delayed increase in serum creatine kinase activity [486 (300) U x l(-1)]. SJ performance decreased markedly immediately after the SSC exercise (P<0.05) and then recovered within 10 min. In contrast, DJ performance and knee joint contribution showed a delayed decrease 2 days after the SSC exercise bout. The surface electromyographic (EMG) activity of the lower limb muscles showed no obvious change in the SJ in comparison to the DJ, although in the latter there was a delayed decrease of knee extensor EMG during the pre-activation and braking phases. The results suggest that isolated concentric muscle function is affected mainly by acute metabolic fatigue after SSC exercise. During a follow-up period after the exercise, changes in hip and knee joint contribution in SJ showed a different recovery pattern compared to those in eccentric DJ. It could be suggested that exhaustive SSC exercise would mainly influence the relative power-work balance between the hip and knee joints during the eccentric phase of SSC. Thus different motor control strategies may account for the distinctive fatigue responses observed in SJ and DJ.

Adult↗

PubMed2002

Acute and prolonged reduction in joint stiffness in humans after exhausting stretch-shortening cycle exercise.

The purpose of the present study was to examine the acute and long-term fatigue effects of exhausting stretch-shortening cycle (SSC) exercise on the stiffness of ankle and knee joints. Five subjects were fatigued on a sledge apparatus by 100 maximal rebound jumps followed by continuous submaximal jumping until complete exhaustion. Neuromuscular fatigue effects were examined in submaximal hopping (HOP) and in maximal drop jumps (DJ) from 35 (DJ35) and 55 cm (DJ55) heights on a force plate. Additional force and reflex measurements were made using an ankle ergometer. Jumping tests and ankle ergometer tests were carried out before, immediately after, 2 h (2H), 2 days and 7 days (7D) after the SSC exercise. Kinematics, force and electromyography (EMG) recordings were complemented with inverse dynamics, which was used to calculate joint moments. The quotient of changes in joint moment divided by changes in joint angle was used as a value of joint stiffness (JS). In addition, blood lactate concentrations and serum creatine kinase activities were determined. The exercise induced a clear decrease in knee joint stiffness by [mean (SD)] 29 (13)% (P < 0.05) in HOP, 31 (6)% (P < 0.05) in DJ35 and 34 (14)% (P < 0.05) in DJ55. A similar trend was observed in the ankle joint stiffness with significant post-exercise reductions of 22 (8)% (P < 0.05) in DJ35 and of 27 (19)% (P < 0.05) at 2H in DJ55. The subsequent recovery of JS was slow and in some cases incomplete still at 7D. Generally, all the EMG parameters were fully recovered by 2H, whereas the force recovery was still incomplete at this time. These data indicate that the immediate reduction in JS was probably related to the effects of both central (neural) and peripheral (metabolic) fatigue, whereas the prolonged impairment was probably due to peripheral fatigue (muscle damage).

Adult↗

PubMed2001

Neuromuscular changes after long-lasting mechanically and electrically elicited fatigue.

Central fatigue was investigated under an isolated active condition whereby the possible effects of supraspinal fatigue were minimized. Therefore, ten subjects were fatigued by simultaneously and repeatedly mechanically stretching and electrically stimulating their calf muscles for 1 h. This was performed using an ankle ergometer. The active fatigue task included a total of 2400 muscle stretches with an intensity of 10% of the maximal voluntary contraction (MVC). This protocol clearly impaired neuromuscular function, as revealed by a significant reduction in MVC (P < 0.01) and the neural input to the muscle (average EMG) (P < 0.01-0.001). The interpolated nerve stimulation compensated for this force loss by 4.28% (P < 0.05). Stretch-reflex recordings revealed a notable post-fatigue reduction in the peak-to-peak amplitude (59.1%, P < 0.01) and stretch-resisting force of the muscle (14.1%, P < 0.01). The maximal H-reflex declined by 50.5% (P < 0.001) and did not recover while the leg was kept ischemic. It is suggested that the existing protocol with minor metabolic loading can induce central fatigue, which seems to be of reflex origin from the fatigued muscle. Although the role of presynaptic inhibition of Ia terminals is possibly reinforced, disfacilitation via reduced spindle sensitivity cannot be excluded.

Adult↗

PubMed2000

Effects of marathon running on running economy and kinematics.

The present study was designed to investigate interactions between running economy and mechanics before, during, and after an individually run marathon. Seven experienced triathletes performed a 5-min submaximal running test on a treadmill at an individual constant marathon speed. Heart rate was monitored and the expired respiratory gas was analyzed. Blood samples were drawn to analyze serum creatine kinase activity (S-CK), skeletal troponin I (sTnI), and blood lactate (B-La). A video analysis was performed (200 frames x s(-1)) to investigate running mechanics. A kinematic arm was used to determine the external work of each subject. The results of the present study demonstrate that after the marathon, a standardized 5-min submaximal running test resulted in an increase in oxygen consumption, ventilation, and heart rate (P < 0.05), with a simultaneous decrease in the oxygen difference (%) between inspired and expired air, and respiratory exchange ratio (P < 0.05). B-La did not change during the marathon, while sTnI and S-CK values increased (P < 0.05), peaking 2 h and 2 days after the marathon, respectively. With regard to the running kinematics, a minor increase in stride frequency and a similar decrease in stride length were observed (P < 0.01). These results demonstrate clearly that weakened running economy cannot be explained by changes in running mechanics. Therefore, it is suggested that the increased physiological loading is due to several mechanisms: increased utilization of fat as an energy substrate, increased demands of body temperature regulation, and possible muscle damage.

Adult↗

PubMed1999

Altered reflex sensitivity after repeated and prolonged passive muscle stretching.

Experiments were carried out to test the effect of prolonged and repeated passive stretching (RPS) of the triceps surae muscle on reflex sensitivity. The results demonstrated a clear deterioration of muscle function immediately after RPS. Maximal voluntary contraction, average electromyographic activity of the gastrocnemius and soleus muscles, and zero crossing rate of the soleus muscle (recorded from 50% maximal voluntary contraction) decreased on average by 23.2, 19.9, 16.5, and 12.2%, respectively. These changes were associated with a clear immediate reduction in the reflex sensitivity; stretch reflex peak-to-peak amplitude decreased by 84. 8%, and the ratio of the electrically induced maximal Hoffmann reflex to the maximal mass compound action potential decreased by 43. 8%. Interestingly, a significant (P < 0.01) reduction in the stretch-resisting force of the measured muscles was observed. Serum creatine kinase activity stayed unaltered. This study presents evidence that the mechanism that decreases the sensitivity of short-latency reflexes can be activated because of RPS. The origin of this system seems to be a reduction in the activity of the large-diameter afferents, resulting from the reduced sensitivity of the muscle spindles to repeated stretch.

Adult↗

PubMed1999

Reduced reflex sensitivity persists several days after long-lasting stretch-shortening cycle exercise.

The mechanisms related to the acute and delayed secondary impairment of the stretch reflex function were investigated after long-lasting stretch-shortening cycle exercise. The results demonstrated a clear deterioration in muscle function immediately after fatigue, which was accompanied by a clear reduction in active and passive reflex sensitivity. For active and passive stretch reflexes, this reduction was biphasic (P < 0.05 to P < 0.001). However, for the ratio of the electrically induced maximal Hoffmann reflex to the maximal mass compound action potential, only one significant reduction was seen immediately after fatigue (71.2%, P < 0.01). A similar significant (P < 0.01) decrease in the stretch-resisting force of the muscle was also detected. Clear increases were found in the indirect markers of muscle damage (serum creatine kinese activity and skeletal troponin I), which could imply the occurrence of ultrastructural muscle damage. It is suggested that the acute reduction in reflex sensitivity is of reflex origin and due to two active mechanisms, disfacilitation and presynaptic inhibition. However, the delayed second decline in the sensitivity of some reflex parameters may be attributable to the secondary injury, because of some inflammatory response to the muscle damage. This might emphasize the role of presynaptic inhibition via group III and IV muscle afferents.

Adult↗

PubMed1998

Interaction between muscle stiffness and stretch reflex sensitivity after long-term stretch-shortening cycle exercise.

The short latency stretch-reflex component (M1) and its interactions with muscle stiffness and with muscle performance were investigated before and after long-term stretch-shortening cycle (SSC) exercise. Dramatic fatigue induced reduction in maximal SSC performance capability, and electromyographic activity was accompanied by a consistent decrease in the M1 reflex component and eccentric peak stiffness of the muscle. It can be suggested, therefore, that the decreased muscle performance is not simply a direct effect of central or peripheral fatigue, but is partly due to impairment of the ability to utilize stiffness-related elastic energy.

Bicycling↗

PubMed1998

Reduced stretch reflex sensitivity and muscle stiffness after long-lasting stretch-shortening cycle exercise in humans.

It has been suggested that during repeated long-term stretch-shortening cycle (SSC) exercise the decreased neuromuscular function may result partly from alterations in stiffness regulation. Therefore, interaction between the short latency stretch-reflex component (M1) and muscle stiffness and their influences on muscle performance were investigated before and after long lasting SSC exercise. The test protocol included various jumps on a sledge ergometer. The interpretation of the sensitivity of the reflex was based on the measurements of the patellar reflexes and the M1 reflex components. The peak muscle stiffness was measured indirectly and calculated as a coefficient of the changes in the Achilles tendon force and the muscle length. The fatigue protocol induced a marked impairment of the neuromuscular function in maximal SSC jumps. This was demonstrated by a 14.1%-17.7% (n.s. - P < 0.001) reduction in the mean eccentric forces and a 17.3%-31.8% (n.s. - P < 0.05) reduction in the corresponding M1 area under the electromyograms. Both of these methods of assessing the short latency reflex response showed a clear deterioration in the sensitivity of the reflex after fatigue (P < 0.05-0.001). This was also the case for the eccentric peak stiffness of the soleus muscle which declined immediately after fatigue by 5.4% to 7.1% (n.s. - P < 0.05) depending on the jump condition. The results observed would suggest that the modulation of neural input to the muscle was at least partly of reflex origin from the contracting muscle, and furthermore, that the reduced muscle stiffness which accompanied the decreased reflex sensitivity could have been partly responsible for the weakened muscle performance due to impaired utilization of elastic energy.

Adult↗

PubMed1997

Leg extension power and walking speed in very old people living independently.

BACKGROUND: Leg extension power can be determined as the product of the force and velocity of movement. Its association with maximal walking speed was studied in 131 80- and 85-year-old men and women. METHODS: Leg extension power was measured with the help of a sledge ergometer in a sitting position using a facilitated "jump test." The participant was attached by belts to a sliding chair on rails inclined at 12.6 degrees to the floor. The feet were placed on the force plate attached perpendicularly to the rails, and the knee angle was 90 degrees at the starting position. The participant was advised to extend his or her legs powerfully. The highest value of five to eight attempts was accepted as the result. The results were adjusted for body mass and expressed as watts.kilogram-1. Maximal walking speed was measured in the laboratory corridor over a distance of 10 m. RESULTS: Men and 80-year-old subjects exhibited greater leg extension power and were faster walkers than women and 85-year-old persons. Leg extension power correlated positively with maximal walking speed in all groups: the correlation coefficients were .412 in the 80-year-old men (n = 41, p = .007), .619 in the 80-year-old women (n = 56, p < .001), .939 in the 85-year-old men (n = 8, p = .001), and.685 in the 85-year-old women (n = 23, p < .001). The regression lines for leg extension power and walking speed were coincident, indicating that the power requirements to attain a given walking speed were similar for both sexes. The minimum power threshold for those with a maximal walking speed of 1.30-1.49 m.s-1 was on the order of 4 W.kg-1; a maximal walking speed of 1.50-1.99 m.s-1 required 7 W.kg-1; and for a speed over 2.00 m.s-1 the power threshold was 9.5 W.kg-1. CONCLUSIONS: Their lower average leg extension power may be one of the factors explaining the greater prevalence of mobility problems among women than men.

Activities of Daily Living↗

PubMed1996

Effects of differently induced stretch loads on neuromuscular control in drop jump exercise.

The neuromuscular characteristics of the triceps surae and vastus lateralis muscles and interactions between the pre-activation of these muscles and the muscle output itself during ground contact were investigated during various types of stretch-shortening cycle muscle loading. The loading of the muscles was effected by using three different types of drop jump exercise. These jumps allowed separate modifications of the loading of the leg extensor muscles by changing the velocity of the centre of gravity (CG) or by changing directly the body mass, which was also affected by changing artificially the acceleration of the CG. It was found that the eccentric peak angular velocity of the ankle joint was related to the various precontact and eccentric parameters in all the different types of jumping exercise. The correlations were higher for the gastrocnemius muscle (P < 0.001) than for the soleus muscle (n.s., P < 0.01). In all the experimental conditions, the pre-activation of the measured muscles started well before the impact of contact with the ground. However, the duration of the pre-activation phase depended on the type of stretch exercise. The results would suggest a clear interaction between the pre-activation of the muscles and that part of the muscle output which is effected by the segmental stretch reflex system. The control mechanism of the pre-activation itself appears to be multiple in character. It seems reasonable to assume that the pre-activation is preprogrammed, but which can, however, be modified by proprioceptive, vestibular and visual inputs. Thus, the possibility of conscious modification of the expected muscle load must be considered.

Adult↗

PubMed1994

Effects of different simulated gravity conditions on neuromuscular control in drop jump exercises.

The neuromuscular characteristics of the triceps surae muscle were investigated during the various types of stretch-shortening cycle (SSC) muscle loading. The analysis concentrated on the preactivation and the contact phases of SSC. Muscle loading was changed unconventionally by artificially changing the condition of the gravity in drop jumps. This was accomplished by using a special lifting block system where the gravity could be modified to control loading and unloading effects of the triceps surae muscle. The normal gravity condition showed an advantage over the other gravity drop jump conditions for the measured parameters. The same tendency could be seen in the activation characteristics of the investigated muscles in the preactivation and eccentric phases. Further, the preactivation EMG was related to the eccentric peak angular velocity of the ankle joint. The correlation coefficients were 0.37 (p < 0.05) and 0.48 (p < 0.01) for the gastrocnemius and the soleus muscles, respectively. All the results emphasized considerable adaptation of the neuromuscular system to the normal gravity condition. However, the overall control of landing may also depend on the vestibular and visual inputs, which might modify even the earlier learned central programs.

Adaptation, Physiological↗