Vesa Linnamo

Acute hormonal responses to submaximal and maximal heavy resistance and explosive exercises in men and women.

The purpose of this study was to examine acute hormonal and neuromuscular responses in men and women to 3 heavy resistance but clearly different exercise protocols: (a) submaximal heavy resistance exercise (SME), (b) maximal heavy resistance exercise (HRE), and (c) maximal explosive resistance exercise (EE). HRE included 5 sets of 10 repetition maximum (10RM) situps, bench press, and bilateral leg extensions (David 210 machine) with a 2-minute recovery between the sets. In SME, the load was 70%, and in EE, the load was 40% from that used in HRE. A significant increase (p < 0.05) in serum growth hormone (GH) was observed after HRE both in men and women, but the increase was greater (p < 0.05) in men than in women. Serum testosterone (T) increased significantly (p < 0.05) only during HRE in men. Since GH and T are anabolic hormones, the acute exercise-induced response during HRE may play an important role in the long-term anabolic adaptation processes related to muscle hypertrophy and maximal strength development.

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.

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.

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. The finding that no difference was observed between M50 and M70 in the force caused by ES alone despite the difference in maximal voluntary force indicated that in addition to the well-known age-related peripheral decrease in muscle mass, maximal voluntary neural activation of these muscles may also decrease to some extent contributing in part to the decrease in strength, especially at older ages.

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

Abstract 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 elecromyogram (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.

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.

Excitability at the Motoneuron Pool and Motor Cortex Is Specifically Modulated in Lengthening Compared to Isometric Contractions

Neural control of muscle contraction seems to be unique during muscle lengthening. The present study aimed to determine the specific sites of modulatory control for lengthening compared with isometric contractions. We used stimulation of the motor cortex and corticospinal tract to observe changes at the spinal and cortical levels. Motor-evoked potentials (MEPs) and cervicomedullary MEPs (CMEPs) were evoked in biceps brachii and brachioradialis during maximal and submaximal lengthening and isometric contractions at the same elbow angle. Sizes of CMEPs and MEPs were lower in lengthening contractions for both muscles (by approximately 28 and approximately 16%, respectively; P < 0.01), but MEP-to-CMEP ratios increased (by approximately 21%; P < 0.05). These results indicate reduced excitability at the spinal level but enhanced motor cortical excitability for lengthening compared with isometric muscle contractions.

Recovery Pattern of Baroreflex Sensitivity after Exercise

PURPOSE To test the association between exercise mode and the recovery pattern of baroreflex sensitivity (BRS) after exercise. METHODS The study population included healthy male subjects (N = 12, age: 31 +/- 3 yr). Four different interventions were performed in a randomized order: 1) aerobic exercise session on a bicycle ergometer, 2) light resistance exercise session, 3) heavy resistance exercise session, and 4) control intervention with no exercise. All interventions lasted 40 min. R-R intervals and continuous blood pressure were measured before (10 min) and 30-180 min after the interventions. BRSLF was calculated by the transfer function method from the low-frequency band (LF, 0.04-0.15 Hz) of the R-R intervals and systolic blood pressure spectra. RESULTS BRSLF had blunted until 30 min after aerobic and light resistance exercise (11.1 +/- 4.3 and 10.0 +/- 3.6 vs 17.5 +/- 7.0 ms.mm Hg(-1), P = 0.002 for both, compared with the control intervention, respectively). However, BRSLF was significantly blunted until 60 min after heavy resistance exercise (9.3 +/- 2.3 vs 15.1 +/- 4.7 ms.mm Hg(-1), P = 0.005, compared with the control intervention). The high-frequency power of R-R intervals (0.15-0.4 Hz) was significantly reduced, and the LF power of systolic blood pressure oscillation was significantly augmented 30 min after heavy resistance exercise (P < 0.01 for both), whereas both indices were restored to the control level by 30 min after aerobic and light resistance exercise. CONCLUSION BRS after acute exercise is associated with exercise intensity, showing relatively rapid recovery after aerobic and light resistance exercise and delayed recovery after heavy resistance exercise. The delayed BRS pattern after heavy resistance exercise is regulated by delicate interplay between the withdrawal of vagal outflow and the probably increased sympathetic vasomotor tone documented by measurements of heart rate and blood pressure variability.

Effect of Skiing Speed on Ski and Pole Forces in Cross-Country Skiing

PURPOSE The present study characterized pole and ski forces in classical technique cross-country skiing. Eight elite junior cross-country skiers performed diagonal skiing at 65%, 75%, 90%, and 100% of maximum speed on a stable 100-m-low uphill (2.5 degrees ). METHOD : The ski and the pole forces (vertical (Fz) and horizontal (Fy) directions) on the right and left sides were recorded separately when the skier skied over a special custom-made force platform system placed at the end of the uphill course. The entire system consisted of four separate 20-m-long rows of 1-m-long force plates connected in series, row by row. RESULTS When the forces were averaged for the various functional phases of skiing cycle, the ski Fz during the gliding phase decreased and the braking ski Fy and Fz remained the same with higher skiing speed. During the subsequent kick phase, both ski Fy and Fz increased significantly as a function of the skiing speed. Consequently, the Fy ratio between the ski and the pole plant increased with faster skiing speed. Simultaneously measured EMGs from five different muscles showed that the abdominals had a pattern of increasing activation with increase in speed of skiing. All the other muscles, vastus lateralis (VL), rectus femoris (RF), erector spinae (ES), and medial gastrocnemius (MG), were obviously active in the preloading and the kick phases. CONCLUSIONS The speed dependence of the ski and the pole force distributions in the present study are important for further understanding of the complexity of cross-country skiing. Especially relevant is to use these results as basis for studies aimed at better understanding of the propulsive force production, when more comprehensive EMG analysis is complemented with simultaneous kinematic recordings at varied slope, speed, and waxing conditions.

Innervation zone shift at different levels of isometric contraction in the biceps brachii muscle

Experiments were carried out to examine whether innervation zone (IZ) location remains stable at different levels of isometric contraction in the biceps brachii muscle (BB), and to determine how the proximity of the IZ affects common surface electromyography (sEMG) parameters. Twelve subjects performed maximal (MVC) and submaximal voluntary isometric contractions at 10%, 20%, 30%, 40%, 50% and 75% of MVC. sEMG signals were recorded with a 13 rows x 5 columns grid of electrodes from the short head of BB. The IZ shifted in the proximal direction by up to 2.4 cm, depending upon the subject and electrode column. The mean shift of all the columns was 0.6+/-0.4 cm (10% vs. 100% MVC, P<0.001). This shift biased the average values of mean frequency (+21.8+/-9.9 Hz, P<0.001), root mean square (-0.16+/-0.15 mV, P<0.05) and conduction velocity (-1.15+/-0.93 m/s, P<0.01) in the channels immediately proximal to the IZ. The shift in IZ could be explained by shortening of the muscle fibers, and thus lengthening of the (distal) tendon due to increasing force. These results underline the importance of individual investigation of IZ locations before the placement of sEMG electrodes, even in isometric contractions.