Biomedical subjects

V Linnamo

Publications and source records attributed to V Linnamo.

14 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↗

PubMed2006

Maximal force during eccentric and isometric actions at different elbow angles.

The purpose of this study was to examine a course of force potentiation and/or inhibition during maximal voluntary eccentric action. Maximal voluntary force (MVC) of elbow flexion of ten healthy male volunteers was measured during isometric and isokinetic eccentric action starting from 80 degrees or 110 degrees and ending at 140 degrees elbow angle. Surface EMG was recorded from biceps brachii (BB) and brachioradialis (BR) muscles. Maximal voluntary eccentric force during the first 10 degrees of the movement was higher (P<0.001) than the maximal voluntary isometric preactivation force both in 80 degrees and in 110 degrees starting position at all three velocities (1, 2, and 4 rad s(-1)). The relative force potentiation was velocity dependent being smallest at the lowest stretching speed (P<0.01). Average EMG (aEMG) of BB and BR decreased as the joint angle increased both in eccentric and in isometric actions but the decrease in aEMG towards extension was somewhat higher in eccentric actions as compared to isometric. It was concluded that the force measured during the first 10 degrees of eccentric contraction always exceeded the maximal voluntary isometric preactivation force regardless of the joint angle or of the movement velocity. When maximal voluntary preactivation preceded the stretch, the relative force potentiation seemed to be greater at higher stretching velocities (velocity dependent) while at lower preactivation levels, the velocity dependence was not observed. Decreased muscle activation and lower maximal voluntary force towards the end of the movement suggested inhibition during maximal voluntary eccentric actions.

Adult↗

PubMed2004

The effects of muscle history on short latency stretch reflex response of soleus muscle.

The purpose of the present study was to investigate the combined effects of muscle history, activation and stretching velocity on short latency stretch response (SLR). Stretches (70, 120 and 200 deg s-1) were elicited to both passive and active (10-25% MVC) triceps surae muscle with constant (ISO), lengthened (LEN) or shortened (SHO) muscle length. Under the passive SHO pre-condition both SLR amplitude and reflex torque (RT) decreased where as latency increased compared with the passive ISO pre-condition. Such observations were absent in active trials. Stretches applied to a lengthening passive muscle (LEN) resulted in smaller SLR amplitude and RT compared with passive ISO. In active muscle the stretch response increased with stretching velocity in ISO and SHO. However, in LEN there was large interindividual variability and no velocity dependent increase in SLR amplitude was observed. Smaller amplitude and longer latency of passive SLR in SHO could result from increased slack in the intrafusal fibres, which may be compensated by fusimotor activation during the active condition. The mechanism behind the smaller amplitude in passive LEN and the lack of velocity dependence in active LEN may be related to changes in motoneuron pool excitability or changes in the spindle sensitivity to stretch.

Adaptation, Physiological↗

PubMed2003

Motor unit activation patterns during isometric, concentric and eccentric actions at different force levels.

Motor unit activation patterns were studied during four different force levels of concentric and eccentric actions. Eight male subjects performed concentric and eccentric forearm flexions with the movement range from 100 degrees to 60 degrees in concentric and from 100 degrees to 140 degrees elbow angle in eccentric actions. The movements were started either from zero preactivation or with isometric preactivation of the force levels of 20, 40, 60 and 80% MVC. The subjects were then instructed to maintain the corresponding relative force levels during the dynamic actions. Intramuscular and surface EMG was recorded from biceps brachii muscle. Altogether 28 motoneuron pools were analyzed using the intramuscular spike-amplitude frequency (ISAF) analysis technique of Moritani et al. The mean spike amplitude was lower and the mean spike frequency higher in the isometric preactivation phase than in the consequent concentric and eccentric actions. When the movements started with isometric preactivation the mean spike amplitude increased significantly (P<0.001) up to 80% in isometric and concentric actions but in eccentric actions the increase continued only up to 60% (P<0.01). The mean spike frequency in isometric preactivation and in concentric action with preactivation was lower only at the 20% force level (P<0.01) as compared to the other force levels while in eccentric action with preactivation the increase between the force levels was significant (P<0.01) up to 60%. When the movement was started without preactivation the mean spike amplitude at 20% and at 40% force level was higher (P<0.01) in eccentric action than in concentric actions. It was concluded that the recruitment threshold may be lower in dynamic as compared to isometric actions. The recruitment of fast motor units may continue to higher force levels in isometric and in concentric as in eccentric actions which, on the other hand, seems to achieve the higher forces by increasing the firing rate of the active units. At the lower force levels mean spike amplitude was higher in eccentric than in concentric actions which might indicate selective activation of fast motor units. This was, however, the case only when the movements were started without isometric preactivation.

Adult↗

PubMed2002

EMG power spectrum and features of the superimposed M-wave during voluntary eccentric and concentric actions at different activation levels.

Muscle fiber conduction velocity (CV) may be affected by the level of voluntary activation and by the diameter of the fiber. Both the frequency component of the electromyography (EMG) power spectrum, such the as median frequency (MF) or mean power frequency, and the duration of muscle compound action potential to single supramaximal electrical impulse (maximal M-wave) may be related to CV. The aim of the present study was to examine how changes in the activation level in lengthening and in shortening conditions would affect the EMG power spectrum during voluntary effort, and compare them to changes in M-wave shape in similar conditions. Ten male subjects performed eccentric and concentric knee extensions at force levels of 40%, 60%, 80% and 100% of maximal eccentric and concentric knee extension force (maximum voluntary contraction, MVC) at an angular velocity of 2 rad.s(-1). In order to measure the M-wave at each force level and in a relaxed condition, a supramaximal electrical stimulus was given to the femoral nerve. The surface EMG was recorded from the vastus lateralis, vastus medialis, and rectus femoris muscles, and the average EMG (aEMG) and MF were calculated. The results show that although the absolute force was greater, the aEMG was generally lower in eccentric as compared to concentric actions at all of the force levels tested. Although the aEMG increased as force increased, no consistent differences were observed in the amplitude of the maximal M-wave in any of the conditions, or in the duration of the M-wave between eccentric and concentric actions. However, as the force level increased the duration of the M-wave decreased significantly ( P<0.01) for both eccentric and concentric actions. On average, no major differences were observed in MF between eccentric and concentric actions or between the force levels in either type of contraction, although rather large variations were observed throughout the motions. In voluntary situations, the recruitment of fast motor units with higher muscle fiber CVs and the increased firing rate of the active units increases the muscle fiber CV as the activation level increases. Even though in conditions of supramaximal electrical nerve stimulation all motor units should be activated simultaneously, the duration of the M-wave in the present study decreased as the force level increased. Possible candidates for the change in the CV may be increased activation of the Na(+)/K(+) pump resulting from the activity in the muscle preceding the electrical stimulation and/or changes in the muscle fiber length between different force levels.

Adolescent↗

PubMed2001

Electromyogram power spectrum and features of the superimposed maximal M-wave during voluntary isometric actions in humans at different activation levels.

The frequency characteristics of the electromyogram (EMG) power spectrum, such as the median or the mean power frequency, as well as the duration of the muscle compound action potential response to a single supramaximal electrical stimulus (maximal M-wave) may both be related to the conduction velocity (CV) of the muscle fibre. To investigate this further, we studied in ten male subjects: the EMG of the vastus lateralis, vastus medialis and rectus femoris muscles during maximal isometric knee extensions at 40%, 60%, 80% and 100% of maximal voluntary contraction and also the maximal M-wave, elicited by a single supramaximal stimulus to the femoral nerve, of the same muscles at rest or superimposed on the same levels of voluntary contraction. The EMG was recorded during the constant force phase of the voluntary contractions, the duration of which was 2.5-4 s, with a 1.5 min pause between contractions. The average EMG (aEMG) and the median frequency (MF) were then calculated. The results indicated that as aEMG increased with increase in force, MF remained unchanged. However, while the amplitude of the M-wave was not affected, the duration of the M-wave was shorter as the force level increased. The duration of the M-wave may be affected by recruitment of faster motor units, by increased firing rate of the active units and by changes in the muscle fibre length. The shorter duration of the M-wave observed at higher force levels was not, however, accompanied by a corresponding increase in MF. The MF could not therefore be used as a parameter to reflect the changes in voluntary muscle activation and CV. When MF was calculated by overlapping the fast Fourier transform (FFT) windows (0.4 s long window moved data point by data point to the right) for 1 s periods of the isometric plateau phase at each force level, the difference between the lowest and the highest MF was quite substantial. These variations suggest that FFT window placement, i.e. which part of the signal is chosen for the analyses, may play an important role even in isometric situations.

Adult↗

PubMed2001

EMG power spectrum and maximal M-wave during eccentric and concentric actions at different force levels.

The aim of the present study was to examine changes in the EMG power spectrum and in the maximal M-wave due to different activation levels of eccentric and concentric actions. Average EMG (aEMG) increased as the force increased but no consistent differences were observed in the amplitude of the maximal M-wave in any of the conditions. However, as the force level increased the duration of the M-wave decreased significantly (P<0.01) both in eccentric and concentric actions while no differences were observed between the action types. On the average, no major differences were observed in median frequency (MF) between any of the conditions, although rather large variations were observed throughout the motions. Increased muscle fiber conduction velocity (CV), as indicated by the decreased duration of the M-wave, could be due to recruitment of fast motor units with higher muscle fiber conduction velocity and increased firing rate of the active units. Also the changes in the muscle fiber length between the force levels may have affected CV.

Adult↗

PubMed2000

Force and EMG power spectrum during and after eccentric and concentric fatigue.

Eccentric and concentric force and median frequency of the EMG power spectrum were measured during and immediately after maximal eccentric (EE) and concentric (CE) exercise and during the recovery period of 1 week. Eight male subjects performed EE and CE consisting of 100 maximal eccentric and concentric actions with elbow flexors during two separate exercise sessions. When comparing maximal eccentric and concentric actions before the exercises, the average force was higher (P<0.001) in eccentric than in concentric but the average rectified EMG (aEMG) values were the same with the two types of action. The average eccentric force decreased 53.3% after EE and 30.6% after CE, while the average concentric force decreased 49.9% after CE and 38.4% after EE. The recovery was slower after EE. The median frequency (MF) of biceps brachii (BB) in eccentric action decreased during both EE (P<0.01) and CE (P<0.05). It recovered within 2 days of the exercises but was lower again (P<0.01) 7 days after EE. In concentric action MF of BB decreased during CE (P<0.01), while no changes were observed in EE. Blood lactate concentration increased (P<0.001) in both exercises and serum creatine kinase (CK) activity increased in EE only, being significantly higher (P<0.001) 7 days after than before the eccentric exercise. In the absolute scale, the eccentric force in EE decreased more than the concentric force in CE (P<0.01). Fatigue response was action type specific as seen in the greater reduction in the force of the exercise type. MF decreased immediately after both exercises, which may be at least partly related to elevated blood lactate concentration. Eccentric actions led to possible muscle damage as indicated by elevated serum CK and muscle soreness, and therefore to longer recovery as compared to concentric actions. Decreased MF after EE may be indicative of selective damage of the fast twitch fibers in this type of exercise.

Adult↗

PubMed2000

Neuromuscular responses to explosive and heavy resistance loading.

The EMG power spectrum may shift towards higher frequencies with higher movement velocities. Fatigue, on the other hand, can cause a decrease in the frequency components. The purpose of this study was to examine acute effects of explosive (EE) and heavy resistance (HRE) concentric leg press exercise on muscle force, EMG and blood lactate. The EE included five sets of ten repetitions with 40+/-6% of the isometric maximum at a 100 degrees knee angle performed as explosively as possible. The same number of repetitions was performed in HRE but with a heavier load (67+/-7% of the isometric maximum at a 100 degrees knee angle). Maximal isometric and single concentric actions of different loads, and an isometric fatigue test were measured before and after both exercises. Surface EMG was recorded from the vastus medialis muscles for analyses of average EMG (aEMG) and EMG power spectrum. Muscle fiber composition of the vastus lateralis was determined and blood lactate measured throughout the exercises. Mean power frequency and median frequency were higher during EE than during HRE (P<0.05). They increased during EE (P<0.05) as the exercise progressed, whereas during HRE no change or even slight decreases were observed. Signs of fatigue after pure concentric work were not observed after EE, and even after HRE, possibly due to the relatively small range of motion and short duration of action time, the fatigue was not that extensive. The relative number of fast twitch fibers was correlated (r=0.87, P<0.05) with the change in blood lactate in HRE. It was concluded that there may be a greater use of fast twitch motor units in explosive movements and that instead of fatigue, the present number of concentric actions in explosive exercise seems to have facilitated the neuromuscular system.

Adult↗

PubMed2000

Force and EMG power spectrum during eccentric and concentric actions.

INTRODUCTION: This study was designed to examine the force and activation levels of elbow flexor muscles during preactivated eccentric, concentric and isometric actions. METHODS: Force, average EMG (aEMG), and the EMG power spectrum were investigated at different constant movement velocities (1 rad x s(-1), 2 rad x s(-1), 3 rad x s(-1), and 4 rad x s(-1)) at different joint angles. RESULTS: Average force at a 110 degree elbow angle was lower and aEMG was higher in concentric actions as compared with eccentric and isometric actions. At a 55 degree elbow angle, there was no difference in aEMG, or it was slightly higher in eccentric actions. MF was higher in the concentric as compared with eccentric actions at the three fastest velocities at the 110 degree elbow angle, whereas no difference was observed at the 55 degree elbow angle. In concentric action, MF was higher in 4 rad x s(-1) in comparison with 1 rads x s(-1) at 110 degree elbow angle. DISCUSSION: These results suggest that it is difficult to maintain the maximal eccentric force throughout the whole range of motion. Maximal EMG activity and frequencies of the EMG power spectrum can be at the same level or lower in eccentric actions as compared with concentric actions, depending on the joint angle and preactivation mode. The results of the EMG power spectrum do not support the concept that in maximal eccentric actions fast units are selectively activated.

Adult↗

PubMed1998

Neuromuscular fatigue and recovery in maximal compared to explosive strength loading.

The purpose of this study was to examine acute neuromuscular fatigue and its recovery in men (n = 8) and women (n = 8). Two strenuous, but clearly different exercises were compared: maximal (MSL) versus explosive strength loading (ESL). The MSL included five sets of ten repetition maximum bilateral leg extensions. The same task and the same number of sets was performed in ESL but with 40% from the load used in MSL and performed as explosively as possible. Isometric force-time curves were measured during maximal voluntary bilateral isometric action of the leg extensors before the fatigue loading and after each set. The measurements were repeated after resting for 1 h, 2 h, 1 day and two days. Surface elecrtomyogram (EMG) activity was recorded from the vastus lateralis, vastus medialis and rectus femoris muscles. Blood samples from the fingertips were also taken throughout the experiment to determine blood lactate concentration. Marked changes took place in both sexes in force production during both MSL and ESL but the overall decreases were greater and the recovery was slower after MSL. Pronounced decreases occurred also in maximal integrated EMG (iEMG). In the men, the decrease in iEMG for the early contraction phase (0-100 ms) during ESL was greater (P < 0.05) than that of MSL, whereas the decrease in iEMG in the peak force phase (500-1500 ms) was similar. As expected, the increase in blood lactate concentration was greater during MSL in both sexes. It was concluded that heavy resistance loading may result in considerable acute fatigue of central and peripheral origin. The reduced electrical activity in the muscles accompanied by an accumulation of blood lactate led to marked decreases in strength. Explosive type loading, especially in men, appeared to lead primarily to central fatigue with less involvement of peripheral fatigue than MSL. The women seemed unable to fatigue themselves as much as the men, particularly in ESL.

Adult↗

PubMed1996

Neuromuscular adaptations during bilateral versus unilateral strength training in middle-aged and elderly men and women.

Twelve middle-aged men and 12 middle-aged women in the 50-year-old age group (M50; range 44-57 years; W50; 43-57), and 12 elderly men and 12 elderly women in the 70-year-old age group (M70; 59-75; W70; 62-75) volunteered as subjects in order to examine effects of 12-week progressive heavy resistance strength training on electromyographic activity (EMG), muscle cross-sectional area (CSA) of the quadriceps femoris and maximal concentric force in a one repetition maximum (1 RM) test of the knee extensor muscles. One half of the subjects in each group performed the knee extension (and flexion) exercises only bilaterally (BIL), while another half performed the exercises only unilaterally (UNIL). None of the subject groups demonstrated statistically significant changes in any of the 1 RM values during the 2 week control period with no training (between week -2 and 0) preceding the actual experimental training. However, the 12-week training resulted in increases (P < 0.05-0.001) in 1 RM values in each group so that the average relative increase of 19 +/- 12% (P < 0.001) in bilateral 1 RM in all BIL trained subjects was greater (P < 0.05) than that of 13 +/- 8% (P < 0.001) recorded for all UNIL trained subjects. The average relative increases of 17 +/- 11% (P < 0.001) and 14 +/- 14% (P < 0.001) in unilateral 1 RM values of the right and left leg in all UNIL trained subjects were greater (P < 0.05) than those of 10 +/- 18% (P < 0.001) and 11 +/- 11% (P < 0.001) recorded for all BIL trained subjects, respectively. The relative average increase of 19 +/- 19% (P < 0.001) observed in the maximum averaged IEMG of both legs during the bilateral actions in all BIL trained subjects was greater (P < 0.05) than that of 10 +/- 17% (P < 0.05) recorded for all UNIL trained subjects. The relative increases of 14 +/- 12% (P < 0.001) and 11 +/- 6% (P < 0.001) recorded for the CSA in all BIL and UNIL trained subjects did not differ significantly from each others. The present findings suggest that progressive heavy resistance strength training leads to great increases in maximal dynamic strength of the trained subjects accompanied by both considerable neural adaptations and muscular hypertrophy not only in middle-aged but also in elderly men and women. Both bilateral and unilateral exercises are effective to produce functional and structural adaptations in the neuromuscular system, although the magnitude of functional strength increase seems to be specific to the type of exercise used, further supporting the principle of specificity in the design of strength programmes.

Adult↗

PubMed1996

Bilateral and unilateral neuromuscular function and muscle cross-sectional area in middle-aged and elderly men and women.

Forty-eight healthy men (M) and women (W), divided into two different age groups, i.e., M50 yrs (range 44-57; n = 12), W50 yrs (range 43-57; n = 12), M70 yrs (range 59-75; n = 12), and W70 yrs (range 62-75; n = 12), volunteered as subjects for examination of muscle cross-sectional area (CSA), maximal voluntary forces, force-time curves, and electromyographic activity of the knee extensor muscles during bilateral and unilateral isometric contractions. The maximal bilateral knee extension force and the average CSA values in M50 were greater (p < .05) than in M70 and in W50 were greater (p < .05-.001) than those recorded for W70. The early forces in the force-time curve were greater (p < .05) for M50 than for M70 and in W50 were greater (p < .05) than in W70. The individual values of the CSA of the left and right quadriceps femoris (QF) correlated (p < .05-.001) with the individual values of maximal unilateral knee extension forces in M50 (r = .87 and r = .87), M70 (r = .61 and r = .80), W50 (r = .79 and r = .58), and W70 (r = .56 and r = .54). When the force values were related to the CSA of the muscle, W70 demonstrated a lower (p < .05) value than the other three groups. Maximal voluntary bilateral forces didn't differ from those of the summed unilateral forces, and the maximal integrated EMG values during the bilateral and unilateral contractions of the same leg were also the same. The results suggest that the decline in maximal strength with increasing age could be related to the decline in the CSA of the muscle, but in older people, especially women, strength decreases seemed to be multifactorial, including possibly a decrease in voluntary neural drive or changes in "qualitative" characteristics of the muscle tissue. Explosive strength may decrease with aging even more than maximal strength, suggesting that atrophying effects of aging may be greater on fast-twitch muscle fibers than on slow-twitch fibers and/or that the rate of neural activation of the muscles may also be influenced by aging. On the other hand, the central nervous system in a simple single joint isometric force production of the knee extensors seems to be capable of activation of the two bilateral QF muscle groups to the same degree in comparison to that of the unilateral activation only.

Adult↗

PubMed1995

Neuromuscular performance in voluntary bilateral and unilateral contraction and during electrical stimulation in men at different ages.

A group of 33 men divided into three different age groups, M30 years (n = 11), M50 years (n = 12) and M70 years (n = 10) volunteered as subjects for examination of their maximal voluntary isometric bilateral and unilateral forces and force-time curves of the knee extensor muscle group as well as electromyogram activity of the vastus lateralis, vastus medialis and rectus femoris muscles of the right and/or left leg contractions. Electrical stimulation (ES) of 50 Hz was also given by two surface tin electrodes for each subject and each leg separately with the maximal tolerable intensity for recording the isometric force evoked. The maximal force produced by the voluntary isometric unilateral knee extension combined with ES was also measured. Maximal voluntary bilateral force of 1142 (SD 82) N in M30 was greater (P < 0.001) and the force of 1094 (SD 228) N in M50 was also greater (P < 0.05) than that of 962 (SD 70) N recorded for M70. The shapes of the isometric force-time curves, especially in absolute values, differed also among the groups so that the force produced during the early positions of the curve were in M30 greater (P < 0.05-0.001) than the force produced M50 and in M70. Neither the maximal voluntary bilateral force per the summed unilateral force nor the average integrated EMG between the bilateral and unilateral conditions differed significantly from each other either in M30, M50 or in M70. The force produced by pure ES was significantly greater in M30 (P < 0.05) than in M50 and M70, but the latter two groups were not significantly different. When ES was combined with the voluntary contractions, the absolute force values declined (P < 0.05-0.001) with increasing age similarly to those forces produced by the voluntary contractions alone. The present results suggest that increasing age results in great decreases both in the maximal voluntary strength and explosive force characteristics of the neuromuscular system but no bilateral deficit may necessarily be observed either in neural activation or in force production in a simple single joint isometric force production task of the knee extensors.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗