Intramuscular energy sources in dogs during physical work

Three groups of dogs were run under different experimental conditions characterized by varying the work load or the running time. Lipid and glycogen analyses were carried out on biopsy specimens from the biceps femoris muscle before and after exercise. In addition, arterial and venous triglycerides and free fatty acids were determined on plasma samples from one group of dogs that had been previously catheterized. Under the conditions of these experiments, results revealed: (1) plasma triglycerides did not contribute significantly to the energy supply for muscle contraction; (2) plasma free fatty acid efflux into muscle was increased during mild exercise but significantly lowered during heavy exercise; (3) exercise did not affect the phospholipid level or its composition in the muscle; and (4) muscle triglyceride levels may increase, decrease, or remain unchanged, depending upon the work load imposed by the exercise.     

Analysis of muscle activation during different leg press exercises at submaximum effort levels

Many studies have analyzed muscle activity during different strength exercises. Although the leg press (LP) is one of the most common exercises performed, there is little evidence of lower limb muscle activity patterns during this exercise and its variations. Thus, this study aimed to verify how mechanical changes and loads affect lower limb muscle activity during the performance of different LP exercises. Fourteen women performed 3 LP exercises: 45 degrees LP (LP45), LP high (LPH), and LP low (LPL) at 40% and 80% of the 1 repetition maximum. The electromyographic activity of the rectus femoris, vastus lateralis, biceps femoris, gastrocnemius, and gluteus maximus was recorded. Results suggested that mechanical changes affect lower limb muscle activity and that it is related to the load used. At moderate effort levels, the rectus femoris and gastrocnemius were more active during the LP45 and LPL than during the LPH. At a high effort level, the rectus femoris and vastus lateralis (quadriceps) were more active during the LPL than the LPH. Again, the rectus femoris and gastrocnemius were more active during the LP45 and LPL than the LPH. On the other hand, gluteus maximus activity was greater during the LPH than the LPL. This study found that coordination patterns of muscle activity are different when performing LP variations at high or moderate effort levels because of mechanical changes and different loads lifted during the different LP exercises. These results suggest that if the goal is to induce greater rectus femoris and vastus lateralis (quadriceps) activation, the LPL should be performed. On the other hand, if the goal is to induce gluteus maximus activity, the LPH should be performed.     

Effect of strength training on pressor reflex responses from receptors in exercising muscles

The effect of strength training on muscle pressor reflex responses was investigated. Ten young, healthy volunteers and eight arm wrestling athletes performed forearm exercises at 30% of maximal voluntary effort until exhaustion. The exercises were either static or rhythmic, with alternating 20-s periods of muscle contraction and relaxation, followed by postexercise forearm arterial occlusion (PEAO). Heart rate, blood pressure (BP), and sympathetic nerve activity directed to muscle blood vessels (MSNA) were continuously recorded during the exercises. MSNA recordings were obtained from the peroneal nerve using a microneurographic method. During static exercises followed by PEAO, there were no differences in BP or MSNA between athletes and nonathlets. In contrast, a significant decrease in muscle pressor reflex responses was observed in the athletes during rhythmic exercises followed by PEAO. The possible relationship between this effect and changes in muscle energy supply, increased wash-out of metabolites, and reduced sensitivity of the muscle receptors in athletes is discussed.     

Electromyographic comparison of the upper and lower rectus abdominis during abdominal exercises

The objective of this pilot study was to determine the effect of 6 different abdominal exercises on the electrical activity of the upper rectus abdominis (URA) and lower rectus abdominis (LRA). Eight healthy, adult volunteers completed 6 random abdominal exercises: curl up, Sissel ball curl up, Ab Trainer curl up, leg lowering, Sissel ball roll out, and reverse curl up. Action potentials were recorded and analyzed from the URA and the LRA using surface electromyography (EMG) during a 2-second concentric contraction. The average normalized data were compared between the URA and the LRA in order to determine the behavior of the different muscle sites and between exercises in order to determine which exercises elicited the highest EMG activity. There were no significant differences (p > 0.05) between the EMG activity of the URA and LRA during any exercise. There were no significant interactions between subject and muscle site or between exercise and muscle site. Significant differences were found among the 6 exercises performed, and due to the interaction between subject and exercise performed. Both the URA and the LRA recorded significantly higher mean amplitudes during the Sissel ball curl up than during all other exercises. In addition, the curl up, Sissel ball curl up, and Ab Trainer curl up had significantly higher normalized EMG activity in both muscle sites than the reverse curl up, the leg lowering exercise, and the Sissel ball roll out. The curl up and the Ab Trainer curl up exercises were not significantly different in terms of their normalized EMG activities for both the URA and the LRA.     

Dynamic joint and muscle forces during knee isokinetic exercise

Isokinetic exercise has been commonly used in knee rehabilitation, conditioning and research in the past two decades. Although many investigators have used various experimental and theoretical approaches to study the muscle and joint force involved in isokinetic knee extension and flexion exercises, only a few of these studies have actually distinguished between the tibiofemoral joint forces and muscle forces. Therefore, the objective of this study was to specify, via an eletromyography(EMG)-driven muscle force model of the knee, the magnitude of the tibiofemoral joint and muscle forces acting during isokinetic knee extension and flexion exercises. Fifteen subjects ranging from 21 to 36 years of age volunteered to participate in this study. A Kin Com exercise machine (Chattecx Corporation, Chattanooga, TN, U.S.A.) was used as the loading device. An EMG-driven muscle force model was used to predict muscle forces, and a biomechanical model was used to analyze two knee joint constraint forces; compression and shear force. The methods used in this study were shown to be valid and reliable (r > 0.84 andp < 0.05). The effects on the tibiofemoral joint force during knee isokinetic exercises were compared with several functional activities that were investigated by earlier researchers. The muscle forces generated during knee isokinetic exercise were also obtained. Based on the findings obtained in this study, several therapeutic justifications for knee rehabilitation are proposed.     

Model of oxygen transport and metabolism predicts effect of hyperoxia on canine muscle oxygen uptake dynamics.

Previous studies have shown that increased oxygen delivery, via increased convection or arterial oxygen content, does not speed the dynamics of oxygen uptake, Vo(2m), in dog muscle electrically stimulated at a submaximal metabolic rate. However, the dynamics of transport and metabolic processes that occur within working muscle in situ is typically unavailable in this experimental setting. To investigate factors affecting Vo(2m) dynamics at contraction onset, we combined dynamic experimental data across working muscle with a mechanistic model of oxygen transport and metabolism in muscle. The model is based on dynamic mass balances for O(2), ATP, and PCr. Model equations account for changes in cellular ATPase, oxidative phosphorylation, and creatine kinase fluxes in skeletal muscle during exercise, and cellular respiration depends on [ADP] and [O(2)]. Model simulations were conducted at different levels of arterial oxygen content and blood flow to quantify the effects of convection and diffusion of oxygen on the regulation of cellular respiration during step transitions from rest to isometric contraction in dog gastrocnemius muscle. Simulations of arteriovenous O(2) differences and (.)Vo(2m) dynamics were successfully compared with experimental data (Grassi B, Gladden LB, Samaja M, Stary CM, Hogan MC. J Appl Physiol 85: 1394-1403, 1998; and Grassi B, Gladden LB, Stary CM, Wagner PD, Hogan MC. J Appl Physiol 85: 1404-1412, 1998), thus demonstrating the validity of the model, as well as its predictive capability. The main findings of this study are: 1) the estimated dynamic response of oxygen utilization at contraction onset in muscle is faster than that of oxygen uptake; and 2) hyperoxia does not accelerate the dynamics of diffusion and consequently muscle oxygen uptake at contraction onset due to the hyperoxia-induced increase in oxygen stores. These in silico derived results cannot be obtained from experimental observations alone.     

Comparison of incremental and steady state tests of endurance training

To compare the results obtained by incremental or constant work load exercises in the evaluation of endurance conditioning, a 20-week training programme was performed by 9 healthy human subjects on the bicycle ergometer for 1 h a day, 4 days a week, at 70-80% VO2max. Before and at the end of the training programme, (1) the blood lactate response to a progressive incremental exercise (18 W increments every 2nd min until exhaustion) was used to determine the aerobic and anaerobic thresholds (AeT and AnT respectively). On a different day, (2) blood lactate concentrations were measured during two sessions of constant work load exercises of 20 min duration corresponding to the relative intensities of AeT (1st session) and AnT (2nd session) levels obtained before training. A muscle biopsy was obtained from vastus lateralis at the end of these sessions to determine muscle lactate. AeT and AnT, when expressed as % VO2max, increased with training by 17% (p less than 0.01) and 9% (p less than 0.05) respectively. Constant workload exercise performed at AeT intensity was linked before training (60% VO2max) to a blood lactate steady state (4.8 +/- 1.4 mmol.l-1) whereas, after training, AeT intensity (73% VO2max) led to a blood lactate accumulation of up to 6.6 +/- 1.7 mmol.l-1 without significant modification of muscle lactate (7.6 +/- 3.1 and 8.2 +/- 2.8 mmol.kg-1 wet weight respectively). It is concluded that increase in AeT with training may reflect transient changes linked to lower early blood lactate accumulation during incremental exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Analysis of heterocyclic amines in food products: interlaboratory studies

A feasibility study and two interlaboratory exercises on the determination of selected heterocyclic amines (HAs) in beef extract, organised in the framework of a European project, are presented. The aim of these exercises was to improve the quality of the laboratories and to evaluate the performance of a standardised analytical method and also the methods currently used by each of the participants for the analysis of these compounds. Three lyophilised portions of a commercial beef material previously spiked with HAs at different concentration levels ranging from 10 to 75 ng g(-1) were used as laboratory reference materials (lot A, B and C). Firstly, a feasibility study was carried out using a test standard solution and the beef extract (lot A), which contained only five HAs. Then, two interlaboratory exercises were carried out using the laboratory reference materials lot B and lot C, containing 10 selected HAs at two different concentration levels, 75 and 10 ng/g, respectively. The results obtained by all participant laboratories using the proposed method showed satisfactory agreement and the CV(%) between-laboratories obtained were from 8.3 to 24.1% for lot B and from 8.7 to 44.5% for lot C. The standardised method evaluated in these collaborative studies is therefore proposed for the analysis of HAs in food material. Moreover, LC-MS is recommended as the most suitable technique for the analysis of a large number of HAs in food samples.     

A surface electromyography based objective method to identify patients with nonspecific chronic low back pain,presenting a flexion related movement control impairment

Movement control impairments (MCI) are often present in patients with non-specific chronic low back pain (NS-CLBP). Therefore, movement control exercises are widely used to rehabilitate patients. However, the objective assessment remains difficult.The purpose of this study was to develop a statistical model, based on logistic regression analysis, to differentiate patients with NS-CLBP presenting a flexion-related MCI from healthy subjects. This model is based on trunk muscle activation patterns measured by surface electromyography (sEMG), during movement control exercises.Sixty-three healthy male subjects and 36 male patients with a flexion-related MCI participated in this study. Muscle activity of the internal obliques, the external obliques, the lumbar multifidus and the thoracic part of the iliocostalis was registered. Ratios of deep stabilizing to superficial torque producing muscle activity were calculated to examine trunk muscle recruitment patterns during 6 different exercises. Logistic regression analyses were performed (1) to define the ratios and exercises that were most discriminating between patients and non-patients, (2) to make a predictive model. K-Fold cross-validation was used to assess the performance of the predictive model.This study demonstrated that sEMG trunk muscle recruitment patterns during movement control tests, allows differentiating NSCLBP patients with a flexion-related MCI from healthy subjects.     

Effects of age and resistance exercise on skeletal muscle interstitial prostaglandin F(2alpha)

Prostaglandin (PG) F2alpha has been shown to contribute to the anabolic events in skeletal muscle. We measured the skeletal muscle interstitial concentration of PGF2alpha at rest and following a standard bout of resistance exercise in eight young (27+/-2 year) and eight old (75+/-4 year) men. Interstitial PGF2alpha concentration was determined from microdialysate samples obtained from two microdialysis probes placed in the vastus lateralis. Microdialysates were collected 1h pre- and 5-6, 8-9, and 24-25 h postexercise. The exercise bout consisted of 4 exercises (3 sets of 8 replications at 80% 1 RM per exercise) emphasizing the quadriceps. Interstitial PGF2alpha levels were not different (P>0.05) between young and old at rest (1.50+/-0.35 vs. 1.52+/-0.30 ng ml-1) or at any time point following the resistance exercise bout. For the young and old combined there was a change (P<0.05) in PGF2alpha levels at 5-6 h (93%) and 8-9 h (95%), which had returned to preexercise levels by 24-25 h. These results show that PGF2alpha is increased in skeletal muscle following a standard bout of resistance exercise and aging does not alter interstitial levels of this PG at rest or after exercise. These data, coupled with previous findings, suggest that the anabolic factor PGF2alpha should be considered when discussing the complex processes that regulate muscle mass in young and old individuals.     

Relationship between muscle fatigue and oxygen uptake during cycle ergometer exercise with different ramp slope increments.

The surface electromyogram (EMG) from active muscle and oxygen uptake (VO2) were studied simultaneously to examine changes of motor unit (MU) activity during exercise tests with different ramp increments. Six male subjects performed four exhausting cycle exercises with different ramp slopes of 10, 20, 30 and 40 W.min-1 on different days. The EMG signals taken from the vastus lateralis muscle were stored on a digital data recorder and converted to obtain the integrated EMG (iEMG). The VO2 was measured, with 20-s intervals, by the mixing chamber method. A non-linear increase in iEMG against work load was observed for each exercise in all subjects. The break point of the linear relationship of iEMG was determined by the crossing point of the two regression lines (iEMGbp). Significant differences were obtained in the exercise intensities corresponding to maximal oxygen uptake (VO2max) and the iEMGbp between 10 and 30, and 10 and 40 W.min-1 ramp exercises (P < 0.05). However, no significant differences were obtained in VO2max and VO2 corresponding to the iEMGbp during the four ramp exercises. With respect to the relationship between VO2 and exercise intensity during the ramp increments, the VO2-exercise intensity slope showed significant differences only for the upper half (i.e. above iEMGbp). These results demonstrated that the VO2max and VO2 at which a nonlinear increase in iEMG was observed were not varied by the change of ramp slopes but by the exercise intensity corresponding to VO2max and the iEMGbp was varied by the change of ramp slopes.(ABSTRACT TRUNCATED AT 250 WORDS)     

The use of functional MRI to evaluate cervical flexor activity during different cervical flexion exercises.

The purpose of this study was to investigate the recruitment pattern of deep and superficial neck flexors evoked by three different cervical flexion exercises using muscle functional MRI. In 19 healthy participants, transverse relaxation time (T2) values were calculated for the longus colli (Lco), longus capitis (Lca), and sternocleidomastoid (SCM) at rest and following three exercises: conventional cervical flexion (CF), craniocervical flexion (CCF), and a combined craniocervical flexion and cervical flexion (CCF-CF). CCF-CF gave the highest T2 increase for all muscles. CCF displayed a significantly higher T2 increase for the Lca compared with the Lco and the SCM. When comparing the CCF and CF, no significant difference was found for the Lca, whereas the Lco and SCM displayed a higher T2 increase during CF compared with CCF. This study shows that muscle functional MRI can be used to characterize the specific activation levels and recruitment patterns of the superficial and deep neck flexors during different cervical flexion exercises. During CCF-CF, all synergists are maximally recruited, which makes this exercise useful for high-load training. CCF may provide a more specific method to assess and retrain Lca muscle performance compared with CF and CCF-CF. This study highlights the need to differentiate between the Lco and Lca when evaluating their function, since these results demonstrate a clear difference in activation of both muscles.     

Resonance in the human medial gastrocnemius muscle during cyclic ankle bending exercise.

We investigated the behavior of the muscle tendon unit (MTU) of the medial gastrocnemius muscle during cyclic ankle bending exercise at eight different frequencies (ranging from 1.33 to 3.67 Hz). The changes in the length of fascicle in the muscle during the exercises were determined by real-time ultrasound imaging. The coordinates of anatomical references and the ground reaction force were determined from video recording and a force plate, respectively. The length change of the MTU (the distance from the origin to insertion of the muscle) was calculated from changes in the knee and ankle joint angles. It was found that the amplitude ratio and phase difference between the fascicle and MTU lengths were both dependent on the movement frequency. At lower frequencies, the fascicle lengths varied almost in phase with the MTU length, whereas they varied out of phase at the higher frequencies. At intermediate frequency, the amplitude of the fascicle became very small compared with that of the MTU, which is considered resonance. We constructed a mechanical model of the MTU based on a notion of forced oscillation in a mass-spring system. The obtained data were well explained by the model. It was concluded that the behavior of the MTU highly depends on the movement frequency due to the viscoelasticity of the MTU.     

Inspiratory muscle fatigue increases sympathetic vasomotor outflow and blood pressure during submaximal exercise

The purpose of this study was to elucidate the influence of inspiratory muscle fatigue on muscle sympathetic nerve activity (MSNA) and blood pressure (BP) response during submaximal exercise. We hypothesized that inspiratory muscle fatigue would elicit increases in sympathetic vasoconstrictor outflow and BP during dynamic leg exercise. The subjects carried out four submaximal exercise tests: two were maximal inspiratory pressure (PI(max)) tests and two were MSNA tests. In the PI(max) tests, the subjects performed two 10-min exercises at 40% peak oxygen uptake using a cycle ergometer in a semirecumbent position [spontaneous breathing for 5 min and with or without inspiratory resistive breathing for 5 min (breathing frequency: 60 breaths/min, inspiratory and expiratory times were each set at 0.5 s)]. Before and immediately after exercise, PI(max) was estimated. In MSNA tests, the subjects performed two 15-min exercises (spontaneous breathing for 5 min, with or without inspiratory resistive breathing for 5 min, and spontaneous breathing for 5 min). MSNA was recorded via microneurography of the right median nerve at the elbow. PI(max) decreased following exercise with resistive breathing, whereas no change was found without resistance. The time-dependent increase in MSNA burst frequency (BF) appeared during exercise with inspiratory resistive breathing, accompanied by an augmentation of diastolic BP (DBP) (with resistance: MSNA, BF +83.4%; DBP, +23.8%; without resistance: MSNA BF, +19.2%; DBP, -0.4%, from spontaneous breathing during exercise). These results suggest that inspiratory muscle fatigue induces increases in muscle sympathetic vasomotor outflow and BP during dynamic leg exercise at mild intensity.     

Effects of exercise order on upper-body muscle activation and exercise performance

With the purpose of manipulating training stimuli, several techniques have been employed to resistance training. Two of the most popular techniques are the pre-exhaustion (PRE) and priority system (PS). PRE involves exercising the same muscle or muscle group to the point of muscular failure using a single-joint exercise immediately before a multi-joint exercise (e.g., peck-deck followed by chest press). On the other hand, it is often recommended that the complex exercises should be performed first in a training session (i.e., chest press before peck-deck), a technique known as PS. The purpose of the present study was to compare upper-body muscle activation, total repetitions (TR), and total work (TW) during PRE and PS. Thirteen men (age 25.08 +/- 2.58 years) with recreational weight-training experience performed 1 set of PRE and 1 set of PS in a balanced crossover design. The exercises were performed at the load obtained in a 10 repetition maximum (10RM) test. Therefore, chest press and peck-deck were performed with the same load during PRE and PS. Electromyography (EMG) was recorded from the triceps brachii (TB), anterior deltoids, and pectoralis major during both exercises. According to the results, TW and TR were not significantly different (p > 0.05) between PRE and PS. Likewise, during the peck-deck exercise, no significant (p > 0.05) EMG change was observed between PRE and PS order. However, TB activity was significantly (p < 0.05) higher when chest press was performed after the peck-deck exercise (PRE). Our findings suggest that performing pre-exhaustion exercise is no more effective in increasing the activation of the prefatigued muscles during the multi-joint exercise. Also, independent of the exercise order (PRE vs. PS), TW is similar when performing exercises for the same muscle group. In summary, if the coach wants to maximize the athlete performance in 1 specific resistance exercise, this exercise should be placed at the beginning of the training session.     

Does force myography recorded at the wrist correlate to resistance load levels during bicep curls?

Resistance strength training is a proven method to improve bone density and muscle strength. A solution capable of automatically detecting the resistance force level exerted by a user from a wrist-based device can offer great convenience to the trainee and hence facilitate a better training outcome. In this short communication, we present our investigation aimed at exploring if force myographic (FMG) signals recorded at the wrist can predict the relative resistance levels that are associated with different weights. Specifically, we investigated the Spearman’s correlations between the wrist FMG signal features and the dumbbell weights during a bicep curl exercise. 10 volunteers were recruited to perform a total of 100 curl actions, which included both the hammer and regular curls while the wrist FMG signals were being recorded. Three sets of weights ranging from 0.2 lb to 8 lb were used. For the hammer curls, a median correlation coefficient of 0.92 with an interquartile range (IQR) of 0.03 was obtained. For the regular curls, a 0.94 median correlation with a 0.02 IQR was obtained. We also used the data from the first 36 curls to generate a classifier model and applied it onto the rest of the data. An averaged validation accuracy of 88% was obtained. The results of this study showed the potential use of wrist FMG signal to detect different levels of the load during exercises; such information could potentially be used as feedback in fitness, sports, and rehabilitation activities.     

Elimination of delayed-onset muscle soreness by pre-resistance cardioacceleration before each set

We compared delayed-onset muscle soreness (DOMS) induced by anaerobic resistance exercises with and without aerobic cardioacceleration before each set, under the rationale that elevated heart rate (HR) may increase blood perfusion in muscles to limit eccentric contraction damage and/or speed muscle recovery. In two identical experiments (20 men, 28 women), well-conditioned athletes paired by similar physical condition were assigned randomly to experimental or control groups. HR (independent variable) was recorded with HR monitors. DOMS (dependent variable) was self-reported using Borg's Rating of Perceived Pain scale. After identical pre-training strength testing, mean DOMS in the experimental and control groups was indistinguishable (P > or = 0.19) for musculature employed in eight resistance exercises in both genders, validating the dependent variable. Subjects then trained three times per week for 9 (men) to 11 (women) weeks in a progressive, whole-body, concurrent training protocol. Before each set of resistance exercises, experimental subjects cardioaccelerated briefly (mean HR during resistance training, 63.7% HR reserve), whereas control subjects rested briefly (mean HR, 33.5% HR reserve). Mean DOMS among all muscle groups and workouts was discernibly less in experimental than control groups in men (P = 0.0000019) and women (P = 0.0007); less for each muscle group used in nine resistance exercises in both genders, discernible (P < 0.025) in 15 of 18 comparisons; and less in every workout, discernible (P < 0.05) in 32% (men) and 55% (women) of workouts. Most effect sizes were moderate. In both genders, mean DOMS per workout disappeared by the fourth week of training in experimental but not control groups. Aerobic cardioacceleration immediately before each set of resistance exercises therefore rapidly eliminates DOMS during vigorous progressive resistance training in athletes.     

Trunk muscle activity during stability ball and free weight exercises

The purpose of this investigation was to compare trunk muscle activity during stability ball and free weight exercises. Nine resistance-trained men participated in one testing session in which squats (SQ) and deadlifts (DL) were completed with loads of approximately 50, 70, 90, and 100% of one-repetition maximum (1RM). Isometric contractions during 3 stability ball exercises (quadruped (QP), pelvic thrust (PT), ball back extension (BE)) were also completed. During all exercises, average integrated electromyography (IEMG) from the rectus abdominus (RA), external oblique (EO), longissimus (L1) and multifidus (L5) was collected and analyzed. Results demonstrate that when expressed relative to 100% DL 1RM, muscle activity was 19.5 +/- 14.8% for L1 and 30.2 +/- 19.3% for L5 during QP, 31.4 +/- 13.4% for L1 and 37.6 +/- 12.4% for L5 during PT, and 44.2 +/- 22.8% for L1 and 45.5 +/- 21.6% for L5 during BE. IEMG of L1 during SQ and DL at 90 and 100% 1RM, and relative muscle activity of L5 during SQ and DL at 100% 1RM was significantly greater (P < or = 0.05) than in the stability ball exercises. Furthermore, relative muscle activity of L1 during DL at 50 and 70% 1RM was significantly greater than in QP and PT. No significant differences were observed in RA and EO during any of the exercises. In conclusion, activity of the trunk muscles during SQs and DLs is greater or equal to that which is produced during the stability ball exercises. It appears that stability ball exercises may not provide a sufficient stimulus for increasing muscular strength or hypertrophy; consequently, the role of stability ball exercises in strength and conditioning programs is questioned. SQs and DLs are recommended for increasing strength and hypertrophy of the back extensors.     

Velocity of isokinetic trunk exercises influences back muscle recruitment patterns in healthy subjects

Isokinetic exercises at different angular velocities on Cybex devices are often used for assessment and therapy in chronic low back pain patients. Little is known about the effect of velocity of movement on the muscle activity during these exercises. The purpose of this study was to investigate both relative muscle activity and ratios of local to global muscle activity at the different velocities of isokinetic movements on a Cybex dynamometer. Fifty-three healthy employees of Belgian Defence (26 male and 27 female) aged between 20 and 57 years old voluntarily performed isometric and isokinetic exercises at four different velocities. Surface electromyographic signals of different abdominal and back muscles were recorded on both sides. Both the relative muscle activity and the local to global muscle activity ratio of the back muscles were affected by changes in velocities of isokinetic exercises. The global muscle system was more influenced by changes in velocity, than the local muscle system. Abdominal relative muscle activity and ratios were not influenced by velocity of movement. This study revealed that the velocity of isokinetic extension exercises influences the recruitment of the back muscles, meaning that protocols of training programs should be adapted in function of the focus of the therapy.     

Electromyographic normalization procedures for determining exercise intensity of closed chain exercises for strengthening the quadriceps femoris muscles

The purpose of this study was to compare the electromyographic (EMG) amplitudes of the quadriceps femoris (QF) muscles during a maximum voluntary isometric contraction (MVIC) to submaximal and maximal dynamic concentric contractions during active exercises. A secondary purpose was to provide information about the type of contraction that may be most appropriate for normalization of EMG data if one wants to determine if a lower extremity closed chain exercise is of sufficient intensity to produce a strengthening response for the QF muscles. Sixty-eight young healthy volunteers (39 female, 29 male) with no lower extremity pain or injury participated in the study. Surface electrodes recorded EMG amplitudes from the vastus medialis obliquus (VMO), rectus femoris (RF), and vastus lateralis (VL) muscles during 5 different isometric and dynamic concentric exercises. The last 27 subjects performed an additional 4 exercises from which a second data set could be analyzed. Maximum isokinetic knee extension and moderate to maximum closed chain exercises activated the QF significantly more than a MVIC. A 40-cm. lateral step-up exercise produced EMG amplitudes of the QF muscles of similar magnitude as the maximum isokinetic knee extension exercises and would be an exercise that could be considered for strengthening the QF muscles. Most published EMG studies of exercises for the QF have been performed by comparing EMG amplitudes during dynamic exercises to a MVIC. This procedure can lead one to overestimate the value of a dynamic exercise for strengthening the QF muscles. We suggest that when studying the efficacy of a dynamic closed chain exercise for strengthening the QF muscles, the exercise be normalized to a dynamic maximum muscle contraction such as that obtained with knee extension during isokinetic testing.