Knee angle-dependent oxygen consumption of human quadriceps muscles during maximal voluntary and electrically evoked contractions

Similar Regional Hypertrophy of the Elbow Flexor Muscles in Response to Low-Load Training With Vascular Occlusion at Short Versus Long Muscle Lengths

BACKGROUND

The regional hypertrophy response of elbow flexor muscles was compared after unilateral elbow flexion training in extended versus flexed shoulder position under vascular occlusion, which can induce muscle hypertrophy in the absence of muscle damage-induced edema/swelling.

HYPOTHESIS

Hypertrophy of elbow flexor muscles would be greater in extended compared with flexed shoulder position.

STUDY DESIGN

Randomized within-subject trial.

LEVEL OF EVIDENCE

Level 2.

METHODS

A total of 21 resistance-trained men (age, 25 ± 5 years; height, 1.78 ± 0.07 m; weight, 79.3 ± 13.1 kg) performed unilateral elbow flexions with one shoulder extended/elbow flexor muscles lengthened/long muscle length (LONG) and the other flexed/elbow flexor muscles shortened/short muscle length (SHORT) under a low-load (30% 1-repetition maximum) vascular occlusion training regimen (15 repetitions per set, 4 sets per session, 4 sessions per week for 3 weeks, using 80% of vascular occlusion pressure). Magnetic resonance imaging measured elbow flexor muscles cross-sectional area (EFCSA) pre- and post-training at 45%, 65%, and 85% of humerus length.

RESULTS

EFCSA significantly increased in both SHORT (P = 0.04) and LONG (P = 0.05) at 45% and 85% lengths (P < 0.01 for both). Changes in EFCSA between SHORT and LONG were statistically similar at the 45% (+6.20% vs +5.08%; Cohen d = 0.006; P = 0.98), 65% (+5.91% vs +3.83%, Cohen d = 0.28, P = 0.30), and 85% lengths (+8.51% vs +7.38%, Cohen d = 0.18,P = 0.56).

CONCLUSION

Muscle hypertrophy of the elbow flexor muscles displayed a similar behavior after low-load elbow flexion training with vascular occlusion performed in the extended versus flexed shoulder position.

CLINICAL RELEVANCE

Therapists, clinicians, and coaches may choose elbow flexion exercises expecting to achieve similar results for hypertrophy in this muscle group, such that exercise selection may rely on availability of equipment in the training room or personal preference.

Acute effects of voluntary isometric contractions at maximal shortening vs. ballistic stretching on flexibility, strength and jump

Background

Isometric training is used in sport, conventional physical activity and rehabilitation. Understandably, there is a great deal of research related to its effect on performance. It is known that the length of the muscle at the moment of contraction is a determinant of strength levels. In the literature we find research on isometric training in short muscle lengths, although it has not been studied in maximally shortened positions or the acute effects that occur after its application. Ballistic stretching (BS) is also popular in sport. Their execution involves actively reaching maximally shortened muscle positions. So far, isometric training has not been compared with protocols involving ballistic stretching. Considering the above, the aim of the present study was to investigate the effects of BS and voluntary isometric contraction at maximal shortening (VICAMS) on range of motion, strength and vertical jump.

Methods

The study involved 60 healthy, physically active individuals (40 and 52 years old) who were randomly assigned to three groups: BS, VICAMS and a control group (CG). To assess acute effects, before and after the intervention, active range of motion (AROM), maximal voluntary isometric force (MVIF) and countermovement jump height (CMJ) were determined.

Results

Time main effects and time*group interactions were found for all variables (p < 0.001). Between-group differences were shown for the VICAMS group after the intervention, with statistically significant higher AROM values compared to the other groups. MVIF values were also higher in the VICAMS group. Intra-group differences were observed for the VICAMS and Ballistic groups, as values on all variables increased from baseline. For the CMJ, intra-group differences showed that both the VICAMS and BS groups improved values compared to baseline values.

Conclusions

The application of VICAMS induced acute improvements over BS in AROM, MVIF and CMJ. These results are important for coaches seeking immediate performance improvement and offer an optimal solution to the warm-up protocol.

Reduced oxygen desaturation in the vastus lateralis of chronic stroke survivors during graded muscle contractions

BACKGROUND

Few studies have examined changes in skeletal muscle physiology post-stroke. This study examined changes in tissue oxygen saturation (StO2) of the vastus lateralis (VL) muscle of stroke survivors and age-matched control participants during maximal and submaximal isometric contractions of the knee extensor muscles.

OBJECTIVES

We hypothesized that tissue oxygen desaturation (ΔStO2) during knee extensor muscle contractions would be less in the VL in the paretic vs. the non-paretic and control legs.

METHODS

Ten chronic stroke survivors (>6 months post-stroke) with lower extremity muscle weakness and 10 age-matched controls completed this prospective cohort study. Maximum voluntary contractions (MVCs) of the knee extensor muscles were assessed with a Biodex dynamometer and StO2 of the VL was measured using near-infrared spectroscopy.

RESULTS

In the paretic leg of the stroke survivors little change in StO2 of the VL was observed during an MVC (ΔStO2 = -1.7 ± 1.8%) compared to the non-paretic (ΔStO2 = -5.1 ± 6.1%; p < 0.05) and control legs (ΔStO2 = -14.4 ± 8.8%; p < 0.05 vs. paretic and non-paretic leg). These differences remained when normalizing for strength differences between the legs. Compared to controls, both the paretic and non-paretic VL showed pronounced reductions in ΔStO2 during ramp and hold contractions equal to 20%, 40%, or 60% of the MVC (p < 0.05 vs. controls at all load levels).

CONCLUSIONS

These results indicate that oxygen desaturation in response to isometric muscle contractions is impaired in both the paretic and non-paretic leg muscle of stroke survivors compared to age-matched controls, and these differences are independent of differences in muscle strength.

Joint angle-specific neuromuscular time course of recovery after isometric resistance exercise at shorter and longer muscle lengths

Resistance training at longer muscle lengths induces greater muscle hypertrophy and different neuromuscular functional adaptations than training at shorter muscle lengths. However, the acute time course of recovery of neuromuscular characteristics after resistance exercise at shorter and longer muscle lengths in the quadriceps has never been described. Eight healthy young participants (4 M, 4 F) were randomly assigned to perform four sets of eight maximal isometric contractions at shorter (SL; 50° knee flexion) or longer (LL; 90° knee flexion) muscle lengths in a crossover fashion. During exercise, peak torque (PT), muscle activity [electromyogram (EMG)], and internal muscle forces were assessed. PT and EMG at shorter (PT50, EMG50) and longer (PT90, EMG90) muscle lengths, creatine kinase (CK), and muscle soreness were measured at baseline, immediately after exercise (Post), after 24 h (24 h), and after 48 h (48 h). During exercise, EMG (P = 0.002) and internal muscle forces (P = 0.017) were greater in LL than in SL. During recovery, there was a main effect of exercise angle, with PT50 (P = 0.002), PT90 (P = 0.016), and EMG50 (P = 0.002) all significantly reduced to a greater degree in LL compared with SL. CK and muscle soreness increased after resistance exercise, but there were no differences between SL and LL. The present results suggest that if the preceding isometric resistance exercise is performed at longer muscle lengths, function and muscle activity at shorter and longer muscle lengths are inhibited to a larger degree in the subsequent recovery period. This information can be used by practitioners to manipulate exercise prescription.NEW & NOTEWORTHY Despite the established long-term benefits of training at longer muscle lengths for muscle size and strength, acutely performing resistance exercise at longer muscle lengths may require a longer time course of neuromuscular recovery compared with performing resistance exercises at shorter muscle lengths. Furthermore, there appear to be different joint angle-specific recovery profiles, depending on the muscle length of the preceding exercise.

Triceps surae muscle hypertrophy is greater after standing versus seated calf-raise training

Background: The triceps surae muscle plays important roles in fundamental human movements. However, this muscle is relatively unresponsive to resistance training (difficult to hypertrophy) but prone to atrophy with inactivity compared with other muscles. Thus, identifying an effective training modality for the triceps surae is warranted. This study compared triceps surae muscle hypertrophy after standing/knee-extended versus seated/knee-flexed plantarflexion (calf-raise) training, where the gastrocnemius is lengthened and shortened, respectively. Methods: Fourteen untrained adults conducted calf-raise training with one leg in a standing/knee-extended position and the other leg in a seated/knee 90°-flexed position at 70% of one-repetition maximum. Each leg performed 10 repetitions/set, 5 sets/session, 2 sessions/week for 12 weeks. Before and after the intervention, magnetic resonance imaging scans were obtained to assess muscle volume of each and the whole triceps surae. Results: Muscle volume significantly increased in all three muscles and the whole triceps surae for both legs (p ≤ 0.031), except for the gastrocnemius muscles of the seated condition leg (p = 0.147-0.508). The changes in muscle volume were significantly greater for the standing than seated condition leg in the lateral gastrocnemius (12.4% vs. 1.7%), medial gastrocnemius (9.2% vs. 0.6%), and whole triceps surae (5.6% vs. 2.1%) (p ≤ 0.011), but similar between legs in the soleus (2.1% vs. 2.9%, p = 0.410). Conclusion: Standing calf-raise was by far more effective, therefore recommended, than seated calf-raise for inducing muscle hypertrophy of the gastrocnemius and consequently the whole triceps surae. This result and similar between-condition hypertrophy in the soleus collectively suggest that training at long muscle lengths promotes muscle hypertrophy.

Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position

The biarticular triceps brachii long head (TB_Long) is lengthened more in the overhead than neutral arm position. We compared triceps brachii hypertrophy after elbow extension training performed in the overhead vs. neutral arm position. Using a cable machine, 21 adults (14 males and 7 females, age: 23.4 ± 1.6 y, height: 1.69 ± 0.09 m, body mass: 64.5 ± 12.4 kg) conducted elbow extensions (90-0°) with one arm in the overhead (Overhead-Arm) and the other arm in the neutral (Neutral-Arm) position at 70% one-repetition maximum (1RM), 10 reps/set, 5 sets/session, 2 sessions/week for 12 weeks. Training load was gradually increased (+5% 1RM/session) when the preceding session was completed without repetition failure. 1RM of the assigned condition and MRI-measured muscle volume of the TB_Long, monoarticular lateral and medial heads (TB_Lat+Med), and whole triceps brachii (Whole-TB) were assessed pre- and post-training. Training load and 1RM increased in both arms similarly (+62-71% at post, P = 0.285), while their absolute values/weights were always lower in Overhead-Arm (-34-39%, P < 0.001). Changes in muscle volume in Overhead-Arm compared to Neutral-Arm were 1.5-fold greater for the TB_Long (+28.5% vs. +19.6%, Cohen's d = 1.272, P < 0.001), 1.4-fold greater for the TB_Lat+Med (+14.6% vs. +10.5%, d = 1.106, P = 0.002), and 1.4-fold greater for the Whole-TB (+19.9% vs. +13.9%, d = 1.427, P < 0.001). In conclusion, triceps brachii hypertrophy was substantially greater after elbow extension training performed in the overhead versus neutral arm position, even with lower absolute loads used during the training.

Three Simulated Goalball Games in the Same Day Cause Central Fatigue and Can Impair Game Technical Performance

The purpose of this study was to investigate the effects of three simulated goalball games on neuromuscular, physiological, perceptual, and technical parameters. Ten male players underwent assessments before and immediately after each game. Heart rate was recorded at rest and during all games that were entirely filmed for further technical performance analysis. Exercise significantly decreased knee extensor muscles peak force and percentage of voluntary activation after the second and third games, indicating the presence of central fatigue. Heart rate responses remained predominantly in a range equivalent to moderate activity intensity in all games. In addition, perceptual parameters were associated with reduced frequency of throws and density of actions. These findings suggest significant implications for the management of physical training, game strategy during a competition, and fixture change from three to two games per day.

Greater Hamstrings Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths

PURPOSE

We investigated the effects of seated versus prone leg curl training on hamstrings muscle hypertrophy and susceptibility to eccentric exercise-induced muscle damage.

METHODS

Part 1: Twenty healthy adults conducted seated leg curl training with one leg (Seated-Leg) and prone with the other (Prone-Leg), at 70% one-repetition maximum (1RM), 10 repetitions per set, 5 sets per session, 2 sessions per week for 12 wk. Magnetic resonance imaging (MRI)-measured muscle volume of the individual and whole hamstrings was assessed pre- and posttraining. Part 2: Nineteen participants from part 1 and another 12 untrained controls (Control-Leg) performed eccentric phase-only leg curl exercise at 90% 1RM, 10 repetitions per set, 3 sets for each of the seated/prone conditions with each leg. MRI-measured transverse relaxation time (T2) and 1RM of seated/prone leg curl were assessed before, 24, 48, and 72 h after exercise.

RESULTS

Part 1: Training-induced increases in muscle volume were greater in Seated-Leg versus Prone-Leg for the whole hamstrings (+14% vs +9%) and each biarticular (+8%-24% vs +4%-19%), but not monoarticular (+10% vs +9%), hamstring muscle. Part 2: After eccentric exercise, Control-Leg had greater increases in T2 in each hamstring muscle (e.g., semitendinosus at 72 h: +52%) than Seated-Leg (+4%) and Prone-Leg (+6%). Decreases in 1RM were also greater in Control-Leg (e.g., seated/prone 1RM at 24 h: -12%/-24%) than Seated-Leg (0%/-3%) and Prone-Leg (+2%/-5%). None of the changes significantly differed between Seated-Leg and Prone-Leg at any time points.

CONCLUSION

Hamstrings muscle size can be more effectively increased by seated than prone leg curl training, suggesting that training at long muscle lengths promotes muscle hypertrophy, but both are similarly effective in reducing susceptibility to muscle damage.

Changes in microvascular oxygenation and total hemoglobin concentration of the vastus lateralis during neuromuscular electrical stimulation (NMES)

Background and Introduction: Neuromuscular electrical stimulation (NMES) is predicated on eliciting muscle contractions and increasing muscle demand to promote increase in strength. Previous studies have shown differences in the magnitude of elicited force among various NMES waveforms but less is known about metabolic demand of muscle during NMES.Objective/Purpose: The purpose of this study was to compare elicited force and muscle metabolic demand during electrically elicited contractions using different NMES waveforms.Methods: A single-session repeated measures design was used. Electrically elicited force (EEF), microvascular oxygenation (SmO2), total hemoglobin concentration ([THC]) of the vastus lateralis, and subject tolerance (VAS score) were measured using three NMES waveforms; burst modulated alternating current (Russian), biphasic pulsed current (VMS®), and burst modulated biphasic pulsed current (VMS-burst®).Results: A significant main effect for waveform was noted for EEF (F = 12.693, p < .001), SmO2 (F = 8.340, p = .001), and VAS (F = 4.213, p = .025), but not [THC]. Compared to Russian current, VMS-burst and VMS resulted in significantly greater EEF (p = .001; p = .009) and local metabolic demand (i.e. decreased SmO2) (p = .005; p = .003), but not [THC]. VAS was significantly greater (p = .023) for VMS (4.2) compared to Russian (3.07) but not different between VMS-burst and Russian and VMS-burst and VMS.Conclusion: Greater muscle force and local metabolic demand were observed with VMS-burst and VMS compared to Russian current. These data provide novel evidence to guide clinical decision making when selecting an NMES waveform.

3D Ultrasound Imaging: Fast and Cost-effective Morphometry of Musculoskeletal Tissue

The developmental goal of 3D ultrasound imaging (3DUS) is to engineer a modality to perform 3D morphological ultrasound analysis of human muscles. 3DUS images are constructed from calibrated freehand 2D B-mode ultrasound images, which are positioned into a voxel array. Ultrasound (US) imaging allows quantification of muscle size, fascicle length, and angle of pennation. These morphological variables are important determinants of muscle force and length range of force exertion. The presented protocol describes an approach to determine volume and fascicle length of m. vastus lateralis and m. gastrocnemius medialis. 3DUS facilitates standardization using 3D anatomical references. This approach provides a fast and cost-effective approach for quantifying 3D morphology in skeletal muscles. In healthcare and sports, information on the morphometry of muscles is very valuable in diagnostics and/or follow-up evaluations after treatment or training.

Local Muscle Metabolic Demand Induced by Neuromuscular Electrical Stimulation and Voluntary Contractions at Different Force Levels: A NIRS Study

Functional Muscle metabolic demand during contractions evoked by neuromuscular electrical stimulation (NMES) has been consistently documented to be greater than voluntary contractions (VOL) at the same force level (10-50% maximal voluntary contraction-MVC). However, we have shown using a near-infrared spectroscopy (NIRS) technique that local muscle metabolic demand is similar between NMES and VOL performed at MVC levels, thus controversy exists. This study therefore compared biceps brachii muscle metabolic demand (tissue oxygenation index-TOI and total hemoglobin volume-tHb) during a 10s isometric contraction of the elbow flexors between NMES (stimulation frequency of 30Hz and current level to evoke 30% MVC) and VOL at 30% MVC (VOL-30%MVC) and MVC (VOL-MVC) level in 8 healthy men (23-33-y). Greater changes in TOI and tHb induced by NMES than VOL-30%MVC confirm previous studies of a greater local metabolic demand for NMES than VOL at the same force level. The same TOI and tHb changes for NMES and VOL-MVC suggest that local muscle metabolic demand and intramuscular pressure were similar between conditions. In conclusion, these findings indicate that NMES induce a similar local muscle metabolic demand as that of maximal VOL.

Neuromuscular adaptations associated with knee joint angle-specific force change

PURPOSE

Neuromuscular adaptations to joint angle-specific force increases after isometric training have not yet been fully elucidated. This study examined angle-specific neuromuscular adaptations in response to isometric knee extension training at short (SL, joint angle 38.1° ± 3.7°) versus long (LL, 87.5° ± 6.0°) muscle lengths.

METHODS

Sixteen men trained three times a week for 6 wk either at SL (n = 8) or LL (n = 8). Voluntary maximal isometric knee extensor (MVC) force, doublet twitch force, EMG amplitudes (EMG/Mmax), and voluntary activation during MVC force (VA%) were measured at eight knee joint angles (30°-100°) at weeks 0, 3, and 6. Muscle volume and cross-sectional area (CSA) were measured from magnetic resonance imaging scans, and fascicle length (Lf) was assessed using ultrasonography before and after training.

RESULTS

Clear joint angle specificity of force increase was seen in SL but not in LL. The 13.4% ± 9.7% (P = 0.01) force increase around the training angle in SL was related to changes in vastus lateralis and vastus medialis EMG/Mmax around the training angle (r = 0.84-0.88, P < 0.05), without changes in the doublet twitch force-angle relation or muscle size. In LL, muscle volume and CSA increased and the changes in CSA at specific muscle regions were correlated with changes in MVC force. A 5.4% ± 4.9% (P = 0.001) increase in Lf found in both groups was not associated with angle-specific force changes. There were no angle-specific changes in VA%.

CONCLUSION

The EMG/Mmax, although not VA%, results suggest that neural adaptations underpinned training-related changes at short quadriceps lengths, but hypertrophic changes predominated after training at long lengths. The findings of this study should contribute to the development of more effective and evidence-based rehabilitation and strength training protocols.

Muscular adaptations and insulin-like growth factor-1 responses to resistance training are stretch-mediated

INTRODUCTION

Modulation of muscle characteristics was attempted through altering muscle stretch during resistance training. We hypothesized that stretch would enhance muscle responses.

METHODS

Participants trained for 8 weeks, loading the quadriceps in a shortened (SL, 0-50° knee flexion; n=10) or lengthened (LL, 40-90°; n=11) position, followed by 4 weeks of detraining. Controls (CON; n=10) were untrained. Quadriceps strength, vastus lateralis architecture, anatomical cross-sectional area (aCSA), and serum insulin-like growth factor-1 (IGF-1) were measured at weeks 0, 8, 10, and 12.

RESULTS

Increases in fascicle length (29±4% vs. 14±4%), distal aCSA (53±12% vs. 18±8%), strength (26±6% vs. 7±3%), and IGF-1 (31±6% vs. 7±6%) were greater in LL compared with SL muscles (P<0.05). No changes occurred in CON. Detraining decrements in strength and aCSA were greater in SL than LL muscles (P<0.05).

CONCLUSIONS

Enhanced muscle in vivo (and somewhat IGF-1) adaptations to resistance training are concurrent with muscle stretch, which warrants its inclusion within training.

Acute microcirculatory effects of medium frequency versus high frequency neuromuscular electrical stimulation in critically ill patients - a pilot study

BACKGROUND

Intensive care unit-acquired weakness (ICUAW) is a common complication, associated with significant morbidity. Neuromuscular electrical stimulation (NMES) has shown promise for prevention. NMES acutely affects skeletal muscle microcirculation; such effects could mediate the favorable outcomes. However, optimal current characteristics have not been defined. This study aimed to compare the effects on muscle microcirculation of a single NMES session using medium and high frequency currents.

METHODS

ICU patients with systemic inflammatory response syndrome (SIRS) or sepsis of three to five days duration and patients with ICUAW were studied. A single 30-minute NMES session was applied to the lower limbs bilaterally using current of increasing intensity. Patients were randomly assigned to either the HF (75 Hz, pulse 400 μs, cycle 5 seconds on - 21 seconds off) or the MF (45 Hz, pulse 400 μs, cycle 5 seconds on - 12 seconds off) protocol. Peripheral microcirculation was monitored at the thenar eminence using near-infrared spectroscopy (NIRS) to obtain tissue O2 saturation (StO2); a vascular occlusion test was applied before and after the session. Local microcirculation of the vastus lateralis was also monitored using NIRS.

RESULTS

Thirty-one patients were randomized. In the HF protocol (17 patients), peripheral microcirculatory parameters were: thenar O2 consumption rate (%/minute) from 8.6 ± 2.2 to 9.9 ± 5.1 (P = 0.08), endothelial reactivity (%/second) from 2.7 ± 1.4 to 3.2 ± 1.9 (P = 0.04), vascular reserve (seconds) from 160 ± 55 to 145 ± 49 (P = 0.03). In the MF protocol: thenar O2 consumption rate (%/minute) from 8.8 ± 3.8 to 9.9 ± 3.6 (P = 0.07), endothelial reactivity (%/second) from 2.5 ± 1.4 to 3.1 ± 1.7 (P = 0.03), vascular reserve (seconds) from 163 ± 37 to 144 ± 33 (P = 0.001). Both protocols showed a similar effect. In the vastus lateralis, average muscle O2 consumption rate was 61 ± 9%/minute during the HF protocol versus 69 ± 23%/minute during the MF protocol (P = 0.5). The minimum amplitude in StO2 was 5 ± 4 units with the HF protocol versus 7 ± 4 units with the MF protocol (P = 0.3). Post-exercise, StO2 increased by 6 ± 7 units with the HF protocol versus 5 ± 4 units with the MF protocol (P = 0.6). These changes correlated well with contraction strength.

CONCLUSIONS

A single NMES session affected local and systemic skeletal muscle microcirculation. Medium and high frequency currents were equally effective.

The use of near-infrared spectroscopy in understanding skeletal muscle physiology: recent developments

This article provides a snapshot of muscle near-infrared spectroscopy (NIRS) at the end of 2010 summarizing the recent literature, offering the present status and perspectives of the NIRS instrumentation and methods, describing the main NIRS studies on skeletal muscle physiology, posing open questions and outlining future directions. So far, different NIRS techniques (e.g. continuous-wave (CW) and spatially, time- and frequency-resolved spectroscopy) have been used for measuring muscle oxygenation during exercise. In the last four years, approximately 160 muscle NIRS articles have been published on different physiological aspects (primarily muscle oxygenation and haemodynamics) of several upper- and lower-limb muscle groups investigated by using mainly two-channel CW and spatially resolved spectroscopy commercial instruments. Unfortunately, in only 15 of these studies were the advantages of using multi-channel instruments exploited. There are still several open questions in the application of NIRS in muscle studies: (i) whether NIRS can be used in subjects with a large fat layer; (ii) the contribution of myoglobin desaturation to the NIRS signal during exercise; (iii) the effect of scattering changes during exercise; and (iv) the effect of changes in skin perfusion, particularly during prolonged exercise. Recommendations for instrumentation advancements and future muscle NIRS studies are provided.

Cerebral and muscle oxygenation changes during static and dynamic knee extensions to voluntary fatigue in healthy men and women: a near infrared spectroscopy study

The aim of the study was to examine the changes in cerebral and muscle blood volume (Cbv, Mbv) and oxygenation (Cox, Mox) during static and dynamic knee extensions to fatigue in men (N=10; 29±9 years) and women (N=14; 27±8 years). After assessment of 1 repetition maximum (1RM) during unilateral knee extensions with the dominant limb, each subject exercised at 50%, 75% and 100% of 1 RM in random order on separate occasions. Simultaneous changes in Cbv, Cox, Mbv and Mox from the contralateral prefrontal lobe and the dominant limb were measured by near infrared spectroscopy. During all three contractions, Cbv and Cox increased while Mbv and Mox decreased until fatigue in both genders. There were no signs of levelling off or decline in Cbv and Cox during any of these contractions, implying that there was no reduction in cerebral neuronal activation. Conversely, there was a rapid decline in Mbv and Mox during the early stages of the contractions, with a plateau or slight increase towards the end. The respective delta values at 50%, 75% and 100% of 1RM for Cbv (0·088 versus 0·062 versus 0·070), Cox (0·042 versus 0·033 versus 0·038), Mbv (-0·225 versus -0·198 versus -0·196), and Mox (-0·169 versus -0·146 versus -0·158) were not significantly different in the total group (N=24). These findings suggest that fatigue during resistance exercise lasting up to 60 s is mediated peripherally because of reduced blood volume and oxygen availability and is independent of the type and intensity of muscle contraction and gender.

Muscle oxygenation of vastus lateralis and medialis muscles during alternating and pulsed current electrical stimulation

This study compared between alternating and pulsed current electrical muscle stimulation (EMS) for muscle oxygenation and blood volume during isometric contractions. Nine healthy men (23-48 years) received alternating current EMS (2500 Hz) modulated at 75 Hz on the knee extensors of one leg, and pulsed current EMS (75 Hz) for the other leg separated by 2 weeks in a randomised, counter-balanced order. Pulse duration (400 μs), on-off ratio (5-15 s) and other stimulation parameters were matched between conditions and 30 isometric contractions were induced at the knee joint angle of 100° (0° full extension). Changes in tissue oxygenation index (∆TOI) and total hemoglobin volume (∆tHb) of vastus lateralis and medialis muscles over 30 contractions were assessed by a near-infrared spectroscopy, and were compared between conditions by a two-way repeated measures ANOVA. Peak torque produced during EMS increased over 30 contractions in response to the increase in the stimulation intensity for pulsed current, but not for the alternating current EMS. The torque during each isometric contraction was less stable in alternating than pulsed current EMS. The changes in ∆TOI amplitude during relaxation phases and ∆tHb amplitude were not significantly different between conditions. However, the decreases in ∆TOI amplitude during contraction phases from baseline were significantly (P < 0.05) greater for the pulsed current than alternating current from the 18th contraction (-15.6 ± 2.3 vs. -8.9 ± 1.8%) to 30th contraction (-10.7 ± 1.8 vs. -4.8 ± 1.5%). These results suggest that the muscles were less activated in the alternating current EMS when compared with the pulsed current EMS.

Comparison between maximal lengthening and shortening contractions for biceps brachii muscle oxygenation and hemodynamics

Eccentric contractions (ECC) require lower systemic oxygen (O2) and induce greater symptoms of muscle damage than concentric contractions (CON); however, it is not known if local muscle oxygenation is lower in ECC than CON during and following exercise. This study compared between ECC and CON for changes in biceps brachii muscle oxygenation [tissue oxygenation index (TOI)] and hemodynamics [total hemoglobin volume (tHb) = oxygenated-Hb + deoxygenated-Hb], determined by near-infrared spectroscopy over 10 sets of 6 maximal contractions of the elbow flexors of 10 healthy subjects. This study also compared between ECC and CON for changes in TOI and tHb during a 10-s sustained and 30-repeated maximal isometric contraction (MVC) task measured immediately before and after and 1–3 days following exercise. The torque integral during ECC was greater ( P < 0.05) than that during CON by ∼30%, and the decrease in TOI was smaller ( P < 0.05) by ∼50% during ECC than CON. Increases in tHb during the relaxation phases were smaller ( P < 0.05) by ∼100% for ECC than CON; however, the decreases in tHb during the contraction phases were not significantly different between sessions. These results suggest that ECC utilizes a lower muscle O2 relative to O2 supply compared with CON. Following exercise, greater ( P < 0.05) decreases in MVC strength and increases in plasma creatine kinase activity and muscle soreness were evident 1–3 days after ECC than CON. Torque integral, TOI, and tHb during the sustained and repeated MVC tasks decreased ( P < 0.01) only after ECC, suggesting that muscle O2 demand relative to O2 supply during the isometric tasks was decreased after ECC. This could mainly be due to a lower maximal muscle mass activated as a consequence of muscle damage; however, an increase in O2 supply due to microcirculation dysfunction and/or inflammatory vasodilatory responses after ECC is recognized.

Biceps brachii muscle oxygenation in electrical muscle stimulation

The purpose of this study was to compare between electrical muscle stimulation (EMS) and maximal voluntary (VOL) isometric contractions of the elbow flexors for changes in biceps brachii muscle oxygenation (tissue oxygenation index, TOI) and haemodynamics (total haemoglobin volume, tHb = oxygenated-Hb + deoxygenated-Hb) determined by near-infrared spectroscopy (NIRS). The biceps brachii muscle of 10 healthy men (23-39 years) was electrically stimulated at high frequency (75 Hz) via surface electrodes to evoke 50 intermittent (4-s contraction, 15-s relaxation) isometric contractions at maximum tolerated current level (EMS session). The contralateral arm performed 50 intermittent (4-s contraction, 15-s relaxation) maximal voluntary isometric contractions (VOL session) in a counterbalanced order separated by 2-3 weeks. Results indicated that although the torque produced during EMS was approximately 50% of VOL (P<0.05), there was no significant difference in the changes in TOI amplitude or TOI slope between EMS and VOL over the 50 contractions. However, the TOI amplitude divided by peak torque was approximately 50% lower for EMS than VOL (P<0.05), which indicates EMS was less efficient than VOL. This seems likely because of the difference in the muscles involved in the force production between conditions. Mean decrease in tHb amplitude during the contraction phases was significantly (P<0.05) greater for EMS than VOL from the 10th contraction onwards, suggesting that the muscle blood volume was lower in EMS than VOL. It is concluded that local oxygen demand of the biceps brachii sampled by NIRS is similar between VOL and EMS.

Reliability of near-infrared spectroscopy for measuring biceps brachii oxygenation during sustained and repeated isometric contractions

We examine the test-retest reliability of biceps brachii tissue oxygenation index (TOI) parameters measured by near-infrared spectroscopy during a 10-s sustained and a 30-repeated (1-s contraction, 1-s relaxation) isometric contraction task at 30% of maximal voluntary contraction (30% MVC) and maximal (100% MVC) intensities. Eight healthy men (23 to 33 yr) were tested on three sessions separated by 3 h and 24 h, and the within-subject reliability of torque and each TOI parameter were determined by Bland-Altman+/-2 SD limits of agreement plots and coefficient of variation (CV). No significant (P>0.05) differences between the three sessions were found for mean values of torque and TOI parameters during the sustained and repeated tasks at both contraction intensities. All TOI parameters were within+/-2 SD limits of agreement. The CVs for torque integral were similar between the sustained and repeated task at both intensities (4 to 7%); however, the CVs for TOI parameters during the sustained and repeated task were lower for 100% MVC (7 to 11%) than for 30% MVC (22 to 36%). It is concluded that the reliability of the biceps brachii NIRS parameters during both sustained and repeated isometric contraction tasks is acceptable.

Comparison between electrically evoked and voluntary isometric contractions for biceps brachii muscle oxidative metabolism using near-infrared spectroscopy

This study compared voluntary (VOL) and electrically evoked isometric contractions by muscle stimulation (EMS) for changes in biceps brachii muscle oxygenation (tissue oxygenation index, DeltaTOI) and total haemoglobin concentration (DeltatHb = oxygenated haemoglobin + deoxygenated haemoglobin) determined by near-infrared spectroscopy. Twelve men performed EMS with one arm followed 24 h later by VOL with the contralateral arm, consisting of 30 repeated (1-s contraction, 1-s relaxation) isometric contractions at 30% of maximal voluntary contraction (MVC) for the first 60 s, and maximal intensity contractions thereafter (MVC for VOL and maximal tolerable current at 30 Hz for EMS) until MVC decreased approximately 30% of pre-exercise MVC. During the 30 contractions at 30% MVC, DeltaTOI decrease was significantly (P < 0.05) greater and DeltatHb was significantly (P < 0.05) lower for EMS than VOL, suggesting that the metabolic demand for oxygen in EMS is greater than VOL at the same torque level. However, during maximal intensity contractions, although EMS torque (approximately 40% of VOL) was significantly (P < 0.05) lower than VOL, DeltaTOI was similar and tHb was significantly (P < 0.05) lower for EMS than VOL towards the end, without significant differences between the two sessions in the recovery period. It is concluded that the oxygen demand of the activated biceps brachii muscle in EMS is comparable to VOL at maximal intensity.

Relative torque contribution of vastus medialis muscle at different knee angles

AIM

We investigated the relative contribution of the vastus medialis (VM) muscle to total isometric knee extension torque at 10 degrees , 30 degrees , 60 degrees and 90 degrees knee flexion. In the past a more prominent role of the VM muscle at more extended knee angles has been put forward. However, different components of the quadriceps muscle converge via a common distal tendon. We therefore hypothesized that the relative contribution of the VM to total knee extension torque would be similar across angles.

METHODS

At each knee angle the EMG isometric torque relations [20%, 25%, 30%, 35% maximal voluntary contraction (MVC)] of the rectus femoris (RF), vastus lateralis (VL) and VM muscle were established in 10 healthy male subjects; rectified surface EMG was normalized to M-wave area. Subsequently, the VM was functionally eliminated by selective electrical surface stimulation with occluded blood flow.

RESULTS

There was no evidence for preferential activation of VM at any of the knee angles. Following VM elimination, total knee extension torque during maximal femoral nerve stimulation (three pulses at 300 Hz) at 10 degrees , 30 degrees , 60 degrees and 90 degrees , respectively, decreased (P < 0.05) to (mean +/- SD): 75.7 +/- 12.2, 75.1 +/- 9.3, 78.2 +/- 7.2 and 76.0 +/- 5.8% (P > 0.05 among knee angles). In addition, during voluntary contractions at 20% MVC the increases in torque output of RF and VL compensating for the loss of VM function were calculated from the increases in EMG and found to be similar (P > 0.05) at 10 degrees , 30 degrees , 60 degrees and 90 degrees values (%MVC), respectively, were: 9.1 +/- 6.8, 7.5 +/- 2.9, 5.9 +/- 3.7 and 6.9 +/- 3.4.

CONCLUSION

The present findings support our hypothesis that the VM contributes similarly to total knee extension torque at different knee angles.