Isometric Contraction Force Research Articles

Quadriceps femoris muscle voluntary isometric force production and relaxation characteristics before and 6 months after unilateral total knee arthroplasty in women

The purpose of the present prospective intervention study was to evaluate voluntary isometric force production, relaxation and activation capacity of the quadriceps femoris (QF) muscle before and 6 months after unilateral total knee arthroplasty (TKA). TKA was performed in ten women with primary knee osteoarthritis (OA) using the condylar endoprostheses. Isometric maximal voluntary contraction (MVC) force, rate of force development at 50% of MVC (RFD50) and their ratio to body mass, half-relaxation time (HRT) and voluntary activation (VA) of the QF muscle were recorded in patients for operated and non-operated leg before and 6 months after TKA. Established characteristics were compared with data on the dominant leg of ten age- and gender-matched controls. The clinical examination was performed using the Knee Society System (KSS) scores and pain intensity was assessed by visual analogue scale. MVC force in operated leg was lower (P < 0.05) before and 6 months after TKA as compared with the non-operated leg (31 and 32%, respectively) and controls (48 and 44%, respectively). Patients had lower (P < 0.05) VA of the QF muscle in operated leg 6 months after TKA as compared to controls. Significant increase (P < 0.05) of KSS clinical scores and the tendency for the increasing of explosive force production of QF muscle in the operated leg were observed 6 months after TKA (RFD50 was 60% lower before TKA and 40% lower 6 months after surgery as compared to controls). When compared with the preoperative value, HRT prolongation (P < 0.05) was noted 6 months after TKA in QF muscle of both legs in patients. Therefore, the present study confirmed that patients with knee OA had reduced force generation ability of QF muscle before TKA and the improvement of explosive force was noted 6 months after surgery.

Effects of Electrotherapy And Icing on Damaged Muscle During Repeated Sets Exercise

PURPOSE: This study investigated which modality would be the best way to improve the recovery of muscle function and immediately performance between two different sets of repeated bouts eccentric exercise. METHODS: Thirty-six non-weight-trained females (29.32 ± 3.58 yrs, 175.75 ± 3.76 cm, 77.00 ± 12.02 kg) participated in this study. All subjects performed the first set of 30 eccentric actions (ECC1) with non-dominate elbow flexors using the dumbbell that was set at 80% of the pre-ECC1 maximal voluntary isometric contraction force (MVC) level, and then subjects were randomly placed into cryotherapy (CTG; n = 12), electrical therapy (ETG; n = 12) or control (CON; n = 12) groups based on their MVC response to ECC1. Immediately after ECC1, cryotherapy and electrical theraphy groups were accepted cold pack and trans cutaneous electrical nerve stimulation (TENS) treatments, respectively, for an hours. Including CON, all subjects were repeated the same bout of 30 eccentric exercise (ECC2) after treatments. MVC were assessed before, immediately after both ECC1 and ECC2, and 2, 4, 7, and 10 days (D2, D4, D7, D10) after ECC1 for all groups. Serum creatine kinase muscle isoform (CK-MM) was collected before, and D2, D4, D7, and D1 0 for all groups. RESULTS: There was a significant further decrease (p <0.01) in MVC immediately after treatment when compared to pre-test for the ETG, but not in CTG and CON. The MVC for ETG were significant decrease than CTG (p <0.05) on day D4, D7, D10, were significant decrease than CON (p <0.05) on D7, D10. There were significant increase in CK-MM on D4, D7 (p <0.05) when compared to pre-test for the ETG, was increase on D4 (p <0.05) for CON, but no significant different between each day for CTG. The CK-MM for ETG were significant increase than CTG and CON on D2, D4, D7 and D10 (p <0.05), and no significant different between CTG and CON on any day. CONCLUSION: The long-term recovery outcomes showed cryotherapy is the most beneficial for muscle damage management between repeated sets, and the short-term outcomes showed cryotherapy and resting are beneficial to the muscle performance, such as muscle strength and active range of motion. Electrical therapy is disadventiaged to manage muscle damage between repeated sets exercise.

Effects of Passive Warm-Up With Ultrasound Diathermy on Exercise Performance and Muscle Damage

PURPOSE: This study investigated the effects of passive warm-up with ultrasound diathermy and heat packing on exercise performance and recovery on muscle damage. METHODS: Eighteen females (22.16±0.84yrs) participated in this study. All of them were involved into three groups as control group (CON), heat packing group (HP) and ultrasound group (USD). CON never received any warm-up protocol before eccentric exercise, HP received 15 minutes of superficial heat with electrical heat pack before exercise, and USD received 7 minutes of deep heat with ultrasound diathermy before exercise. Each subject processed 30 repeated bouts of eccentric exercise with 80% maximal voluntary isometric contraction force (MVC) level. Serum creatine kinase muscle isoform (CK-MM), MVC, range of motion (ROM) and cross section area of biceps brachii (CSA) were measured before, immediately after exercise and at 2nd, 4th, 7th, and 10th days post-exercise. RESULTS: When measuring serum CK-MM and CSA, there were no significant difference between CON, HP and USD (P > 0.05). When measuring ROM and MVC, there were significant difference between CON, HP and USD (p < 0.05).FigureCONCLUSION: Passive warm-up with ultrasound diathermy and heat packing have better performance in muscle strength and range of motion in eccentric exercise. According to the recovery procedure, Subjects of USD group took lesser damage on muscles than HP and CON. USD group had lesser swelling then other groups in recovery stage after eccentric contraction exercise.

Effects of exhaustive stretch‐shortening cycle exercise on muscle blood flow during exercise

The influence of exhaustive stretch-shortening cycle exercise (SSC) on skeletal muscle blood flow (BF) during exercise is currently unknown. Quadriceps femoris (QF) BF was measured in eight healthy men using positron emission tomography before and 3 days after exhaustive SSC exercise. The SSC protocol consisted of maximal and submaximal drop jumps with one leg. Needle biopsies of the vastus lateralis muscles were taken immediately and 2 days after SSC for muscle endothelial nitric oxide synthase (eNOS) and interleukin-1-beta (IL-1beta) mRNA level determinations. All subjects reported subjective muscle soreness after SSC (P < 0.001), which was well in line with a decrease in maximal isometric contraction force (MVC) and increase in serum creatine kinase activity (CK) (P = 0.018). After SSC muscle BF was 25% higher in entire QF (P = 0.043) and in its deep and superficial muscle regions, whereas oxygen uptake remained unchanged (P = 0.893). Muscle biopsies revealed increased IL-1beta (30 min: 152 +/- 75%, P = 0.012 and 2 days: 108 +/- 203%, P = 0.036) but decreased or unchanged eNOS (30 min; -21 +/- 57%, P = 0.050 and 2 days: +101 +/- 204%, P = 0.779) mRNA levels after SSC. It was concluded that fatiguing SSC exercise induces increased muscle BF during exercise, which is likely to be associated with pro-inflammatory processes in the exercised muscle.

Head repositioning errors in normal student volunteers: a possible tool to assess the neck's neuromuscular system

BackgroundA challenge for practitioners using spinal manipulation is identifying when an intervention is required. It has been recognized that joint pain can interfere with the ability to position body parts accurately and that the recent history of muscle contraction can play a part in that interference. In this study, we tested whether repositioning errors could be induced in a normal population by contraction or shortening of the neck muscles.MethodsIn the experimental protocol, volunteers free of neck problems first found a comfortable neutral head posture with eyes closed. They deconditioned their cervical muscles by moving their heads 5 times in either flexion/extension or lateral flexion and then attempted to return to the same starting position. Two conditioning sequences were interspersed within the task: hold the head in an extended or laterally flexed position for 10 seconds; or hold a 70% maximum voluntary contraction in the same position for 10 seconds. A computer-interfaced electrogoniometer was used to measure head position while a force transducer coupled to an auditory alarm signaled the force of isometric contraction. The difference between the initial and final head orientation was calculated in 3 orthogonal planes. Analysis of variance (1-way ANOVA) with a blocking factor (participants) was used to detect differences in proprioceptive error among the conditioning sequences while controlling for variation between participants.ResultsForty-eight chiropractic students participated: 36 males and 12 females, aged 28.2 ± 4.8 yrs. During the neck extension test, actively contracting the posterior neck muscles evoked an undershoot of the target position by 2.1° (p <0.001). No differences in repositioning were found during the lateral flexion test.ConclusionThe results suggest that the recent history of cervical paraspinal muscle contraction can influence head repositioning in flexion/extension. To our knowledge this is the first time that muscle mechanical history has been shown to influence proprioceptive accuracy in the necks of humans. This finding may be used to elucidate the mechanism behind repositioning errors seen in people with neck pain and could guide development of a clinical test for involvement of paraspinal muscles in cervical pain and dysfunction.

Diurnal changes in the amplitude of the Hoffmann reflex in the human soleus but not in the flexor carpi radialis muscle

Changes in the reflex amplitude throughout the day have been observed in non-human mammals. The present experiment tested whether diurnal fluctuations also occur in humans. Hoffmann reflex (H-reflex) amplitude was measured in soleus and flexor carpi radialis (FCR) muscles from the data collected over a 12-h period between 7:00-9:00 a.m. and 7:00-9:00 p.m. At 4-h intervals, M/H recruitment curves were obtained, and two measures of H-reflex excitability were calculated. The maximal H-reflex (H (max)) was calculated as the average of the three largest H-reflexes. H-reflexes were also sampled from the ascending limb of the M/H recruitment curve (H (A), n=10), with a corresponding M-wave of 5% M (max). All values were normalized to the maximal M-wave (M (max)). Soleus H-reflex amplitude and plantar flexion maximal voluntary isometric contraction force (MVIC) were significantly smaller (p<0.05) in the morning (H (max)=57.2% M (max), H (A)=42.3%, M (max), MVIC=162.1 Nm) than in the evening (H (max)=69.1% M (max), a 20.1% increase, H (A)=54.1% M (max), a 27.4% increase and MVIC=195.8 Nm, a 20.8% increase). In contrast, FCR H-reflex amplitude and FCR MVIC were unchanged across all testing sessions. The data show that diurnal fluctuations are present in the amplitude of the human soleus but not in the FCR H-reflex. Diurnal fluctuation in the human soleus H-reflex amplitude must be considered when interpreting H-reflex data, especially when a repeated measures design spanning several days is utilized.

Changes of motor drive, cortical arousal and perceived exertion following prolonged cycling to exhaustion

The aims of this study were to (1) quantify any central fatigue that occurs following prolonged dynamic exercise, i.e. reduced muscle force caused by impaired motor drive from the central nervous system and (2) determine whether decreased cortical arousal, assessed using critical flicker fusion threshold (CFF), occurs and is related to impaired exercise performance. Fifteen healthy men cycled at 70% VO2peak until exhaustion. The peak force of maximum voluntary isometric contractions (MVC) of the quadriceps muscle group was reduced by 30% at exhaustion. The voluntary activation ratio determined using superimposed tetanic stimulation fell from 0.99 to 0.86 at exhaustion. The central fatigue (%) at exhaustion was 33+/-12% (+/- SD) (assessed via the tetanus interpolation technique) and 54+/-32% (assessed via the relative decline of MVC and peak tetanic force) of the total fatigue. The MVC only partially recovered and central fatigue persisted at 30 min post-exercise. CFF increased from 39.2+/-2.3 to 41.8+/-3.5 Hz at exhaustion, but did not correlate with central fatigue. Every subject reached the highest rating of perceived exertion (RPE) at exhaustion of 20 on the Borg scale. The time to exhaustion was related to how quickly the RPE increased and to the ability to sustain exercise at very high RPE. These data suggest that with prolonged cycling: (1) there is considerable and a persistent form of central fatigue, (2) there is an increased level of cortical arousal, and (3) exhaustion is linked to very high subjective RPE.

Quantitating progression in ALS

The authors prospectively studied the value of clinical and neurophysiologic measurements in assessing progression in ALS. Motor unit number estimation (MUNE) and the neurophysiologic index (NI) were significantly correlated with ADM strength (maximal voluntary isometric contraction force in the abductor digiti minimi muscle [MVIC-ADM]). MUNE and the NI were reliable, but the NI showed a lower variation. On assessing progression at 3, 6, and 12 months, MUNE, NI, and MVIC-ADM showed the highest rate of change. The NI is a potentially useful new neurophysiologic measurement.

Effects Of Age And ACL Injury On Quadriceps Gamma Loop Function

Significant muscular strength deficits are recognizable in the quadriceps muscles of both aging and ACL reconstructed individuals. These strength deficits can have a significant negative impact on functional independence, so it is both clinically and theoretically important to fully understand the possible mechanisms responsible for strength decrements associated with increasing age and ACL reconstructions. It appears that the common link between the conditions of aging and ACL reconstruction may lie in the gamma spindle system, or the gamma loop. Purpose Therefore, the purpose of this study was to investigate the effects of age and ACL reconstruction on gamma loop function. Methods Differences in isometric maximal voluntary contraction (MVC) forces and quadriceps EMG activity (vastus lateralis, vastus medialis, rectus femoris) of young healthy (n = 14; mean age 23.8 yrs), young ACL reconstructed (n = 7; mean age 22.4 yrs), and older healthy individuals (n = 14; mean age 66.1 yrs) were quantified both before and after vibration stimulation application to the infrapatellar tendon using a percussion hammer (50 Hz, 30 N, 20 min). A two-way ANOVA with repeated measures was used to evaluate group and time main effects with a Bonferroni post hoc analyses. Results The young healthy group's MVC force (p = 0.001), vastus lateralis EMG (p = 0.012), vastus medialis EMG (p = 0.002), and rectus femoris EMG (p = 0.003) declined following vibration stimulation to the infrapatellar tendon, indicating an intact gamma loop, whereas both the old healthy and ACL reconstructed groups showed no decline in either force or EMG activity. Conclusion Gamma loop function was impaired in both the older and ACL reconstructed groups possibly due to the loss of mechanoreceptors in the ACL reconstructed group and decreased muscle spindle sensitivity in the older group.Table

Effects Of Age And ACL Injury On Quadriceps Gamma Loop Function

Significant muscular strength deficits are recognizable in the quadriceps muscles of both aging and ACL reconstructed individuals. These strength deficits can have a significant negative impact on functional independence, so it is both clinically and theoretically important to fully understand the possible mechanisms responsible for strength decrements associated with increasing age and ACL reconstructions. It appears that the common link between the conditions of aging and ACL reconstruction may lie in the gamma spindle system, or the gamma loop. Purpose Therefore, the purpose of this study was to investigate the effects of age and ACL reconstruction on gamma loop function. Methods Differences in isometric maximal voluntary contraction (MVC) forces and quadriceps EMG activity (vastus lateralis, vastus medialis, rectus femoris) of young healthy (n = 14; mean age 23.8 yrs), young ACL reconstructed (n = 7; mean age 22.4 yrs), and older healthy individuals (n = 14; mean age 66.1 yrs) were quantified both before and after vibration stimulation application to the infrapatellar tendon using a percussion hammer (50 Hz, 30 N, 20 min). A two-way ANOVA with repeated measures was used to evaluate group and time main effects with a Bonferroni post hoc analyses. Results The young healthy group's MVC force (p = 0.001), vastus lateralis EMG (p = 0.012), vastus medialis EMG (p = 0.002), and rectus femoris EMG (p = 0.003) declined following vibration stimulation to the infrapatellar tendon, indicating an intact gamma loop, whereas both the old healthy and ACL reconstructed groups showed no decline in either force or EMG activity. Conclusion Gamma loop function was impaired in both the older and ACL reconstructed groups possibly due to the loss of mechanoreceptors in the ACL reconstructed group and decreased muscle spindle sensitivity in the older group.Table

Resistance Training Improves Knee Extension Power, Contractile Velocity, And Fatigue Resistance In Older Men And Women

Muscle power exhibits greater age-related declines than strength consequent to marked declines in maximum contractile velocity. Further, older adults are less capable of sustaining maximum concentric velocity during repetitive contractions than young adults. PURPOSE To investigate the effects of 16 wk progressive resistance training (PRT) on knee extension (KE) power, contractile velocity, and fatigability in older versus young adults. METHODS Nineteen young (27.3 ± 1 yr, 9 men) and 18 older (64.1 ± 1 yr, 10 men) adults trained knee extensors 3 d/wk via knee extension, leg press, and squat, each for 3 sets × 8–12 repetitions, with training loads of 70–80% onerepetition maximum (1RM). Testing occurred at baseline, 8 and 16 wk post-training. Dynamic peak strength (1RM) was the heaviest load lifted with full range of motion. Peak concentric KE power was determined across a load spectrum of 5 submaximal loads relative to maximum isometric voluntary contraction (MVC) force (20, 30, 40, 50, 60% MVC). Fatigability was measured by a decline in peak contractile velocity across 10 reps of KE using an external load equal to 40% MVC. Peak concentric velocity was encouraged during power and fatigue tests. Thigh lean mass (TLM) was measured by DEXA. RESULTS Men and women increased KE 1RM (p<0.05) by 8 wk with men also increasing strength from 8 to 16 wk. Adjusting for TLM, all groups increased KE specific strength from baseline (p<0.05). For the KE load-power curve, there was an upward displacement for all subjects (p<0.05) by 8 wk but no further increase from 8 to 16 wk. Tukey's HSD post-hoc testing revealed this upward displacement was driven primarily by older men, the only age-gender sub-group to increase by 8 wk (p<0.05). Because MVC increased, absolute loads lifted during power testing increased by 8 wk (p<0.05). Even at heavier loads, increased peak contractile velocity was found at each load up to 60% MVC (p<0.05). Increases in contractile velocity were driven primarily by older men. Fatigability tested at baseline showed no decline in peak contractile velocity across 10 repetitions in the young group while the older group showed fatigue (−17%, p<0.05). After training 8 wk, neither group exhibited significant fatigue. At 16 wk, the older group fatigued 12% as peak contractile velocity increased but 10th repetition velocity was unchanged. CONCLUSIONS Conventional PRT increased strength, power, and contractile velocity in older adults, particularly in older men. PRT also enhanced fatigue resistance in older adults during repetitive contractions. Future studies should examine the efficacy of power training in older adults, especially in older women. Sponsored by NIA R01 AG17896.

Effects Of Different Modalities On The Muscular Function Between Repeated Bouts Of Exercise

PURPOSE To investigated which modality would be the best way to improve the recovery of muscle function between two different sets of repeated bouts of eccentric exercise. METHODS: Thirty-six non-weight-trained subjects (age: 21.23 ± 1.68 yrs, Ht: 163.56 ±6.67 cm, Wt: 54.63 ± 6.84 kg) participated in this study. All subjects performed the first set of 30 eccentric actions (ECC1) with non-dominal elbow flexor using a dumbbell that was set at 80% of the pre-ECC1 maximal voluntary isometric contraction (MVC) force. Subjects were then randomly placed into cryotherapy (CRYO; n = 12), electrical therapy (ELEC; n = 12) or control (CON; n = 12) groups. Immediately after ECC1, the CRYO and ELEC groups received cold and transcutaneous electrical nerve stimulation (TENS) treatments, respectively, for an hour. All subjects repeated the same bout of 30 eccentric exercise (ECC2) after treatments. The MVC was assessed before, immediately after both ECC1 and ECC2, and 2, 4, 7, and 10 days (D2, D4, D7, D10) after ECC1 for all groups. Serum creatine kinase isoform (CK-MM) was analyzed before, and at D2, D4, D7, and D1 0 for all groups. RESULTS There was a significant further decrease (P < 0.05) in MVC immediately after treatment when compared to the pre-test for the ELEC, but not for CRYO and CON. The MVC for ELEC was significantly lower than CRYO (P < 0.05) on day D4, D7 and D10. The MVC of ELEC was also significantly lower than CON (P < 0.05) on D7 and D10. There was a significant increase in CK-MM on D4 and D7 (P < 0.05) when compared to the pre-test for the ELEC, increased CK-MM on D4 (P < 0.05) for CON, but no significant difference among days for CRYO. The CK-MM for ELEC was significantly greater than CRYO and CON on D2, D4, D7 and D10 (P < 0.05). However, there were no significant differences between CRYO and CON on any day. CONCLUSIONS The recovery outcomes showed cryotherapy is the most beneficial for muscle damage management between repeated sets, and lower frequency electrical therapy is the least usefal for muscular function recovery.

Effects Of Different Modalities On The Muscular Function Between Repeated Bouts Of Exercise

PURPOSE To investigated which modality would be the best way to improve the recovery of muscle function between two different sets of repeated bouts of eccentric exercise. METHODS: Thirty-six non-weight-trained subjects (age: 21.23 ± 1.68 yrs, Ht: 163.56 ±6.67 cm, Wt: 54.63 ± 6.84 kg) participated in this study. All subjects performed the first set of 30 eccentric actions (ECC1) with non-dominal elbow flexor using a dumbbell that was set at 80% of the pre-ECC1 maximal voluntary isometric contraction (MVC) force. Subjects were then randomly placed into cryotherapy (CRYO; n = 12), electrical therapy (ELEC; n = 12) or control (CON; n = 12) groups. Immediately after ECC1, the CRYO and ELEC groups received cold and transcutaneous electrical nerve stimulation (TENS) treatments, respectively, for an hour. All subjects repeated the same bout of 30 eccentric exercise (ECC2) after treatments. The MVC was assessed before, immediately after both ECC1 and ECC2, and 2, 4, 7, and 10 days (D2, D4, D7, D10) after ECC1 for all groups. Serum creatine kinase isoform (CK-MM) was analyzed before, and at D2, D4, D7, and D1 0 for all groups. RESULTS There was a significant further decrease (P < 0.05) in MVC immediately after treatment when compared to the pre-test for the ELEC, but not for CRYO and CON. The MVC for ELEC was significantly lower than CRYO (P < 0.05) on day D4, D7 and D10. The MVC of ELEC was also significantly lower than CON (P < 0.05) on D7 and D10. There was a significant increase in CK-MM on D4 and D7 (P < 0.05) when compared to the pre-test for the ELEC, increased CK-MM on D4 (P < 0.05) for CON, but no significant difference among days for CRYO. The CK-MM for ELEC was significantly greater than CRYO and CON on D2, D4, D7 and D10 (P < 0.05). However, there were no significant differences between CRYO and CON on any day. CONCLUSIONS The recovery outcomes showed cryotherapy is the most beneficial for muscle damage management between repeated sets, and lower frequency electrical therapy is the least usefal for muscular function recovery.

Overcoming Peripheral Nerve Gap Defects Using an Intact Nerve Bridge in a Rabbit Model

This study investigated the intact nerve bridge technique for overcoming peripheral nerve gap defects in a rabbit model. To create the intact nerve bridge, a 1-cm segment of the peroneal nerve is resected leaving a gap defect. The proximal and distal peroneal nerve stumps are sutured 1 cm apart, in an end-to-side fashion, to the intact tibial nerve epineurium. Four experimental groups were used (n = 10): primary repair of resected segment; intact nerve bridge; nerve autograft; and gap in situ control. Evaluation after 12 weeks included measurement of isometric muscle contraction force, axonal counting, wet muscle weights, and histologic examination. The results of this study support two main conclusions, in a rabbit model: (a) regenerating axons can use the epineurium of an intact nerve to bridge a gap defect; (b) there is no significant difference in the functional recovery between standard nerve autografts and the intact nerve bridge technique.

Torque Responses in Human Quadriceps to Burst-Modulated Alternating Current at 3 Carrier Frequencies

Independent group design, 1 group per carrier frequency, with subjects stratified by gender and systematically assigned to groups. To determine the effect of the frequency of burst-modulated alternating current (AC) on the electrically induced torque (EIT) response of the quadriceps femoris muscle. Many studies have examined the influence of current amplitude and burst modulation on the EIT response. However, research is limited on the effects of carrier frequency on the EIT response of the quadriceps femoris. Twenty-three healthy subjects (mean age +/- SD, 22.7 +/- 1.7 years) volunteered for the study and were systematically assigned to 1 of 3 groups: group 1 (2500-Hz AC), group 2 (3750-Hz AC), and group 3 (5000-Hz AC). For normalization purposes, maximal voluntary isometric contraction (MVIC) force was assessed with a load cell prior to the application of 5 minutes of neuromuscular electrical stimulation (NMES). The EIT and current amplitude were recorded during each of the 5 minutes of NMES. The mean EIT ([EIT/MVIC] x 100) produced at equivalent current amplitudes when using the 2500-Hz carrier frequency was significantly greater than the mean EITs generated at 3750 Hz (P = .004) and 5000 Hz (P<.001), respectively. Burst-modulated alternating current delivered at 2500 Hz produced greater EITs than those generated at 3750 and 5000 Hz.

Fluctuations in motor output during steady contractions are weakly related across contraction types and between hands

The presence of differences in motor unit activity across contraction types and between hands suggests that the magnitude of fluctuations in motor output is only weakly related when these conditions are compared. Twenty right-handed young (24.1 +/- 5.3 years) and old (72.5 +/- 4.9 years) adults performed three levels (</=40% of maximal force) of isometric and anisometric contractions with the first dorsal interosseous muscle of each hand. The fluctuations in motor output were quantified by the coefficient of variation for force during isometric contractions, and as the standard deviations of acceleration and position during anisometric contractions. There was no effect of age on fluctuations in motor output. The magnitude of the fluctuations in motor output was weakly related across contraction types (r(2) < 0.325) and between hands (r(2) < 0.262). Furthermore, the standard deviations of acceleration and position during shortening and lengthening contractions were largely unrelated to one another. Because the activity in a motor unit population differed across contraction types and hands during steady contractions, the central nervous system likely employed distinct strategies to accomplish these different tasks.

The Inotropic and Lusitropic Effects of Ketamine in Isolated Human Atrial Myocardium: The Effect of Adrenoceptor Blockade

We studied the direct myocardial effects of racemic ketamine, in the presence of alpha- and beta-adrenoceptor blockade, on isolated human right atrial myocardium. Isometric force of contraction (FoC), its first derivative with time (+dF/dt), the contraction relaxation coupling parameter R2 = (+dF/dt) / (-dF/dt), and time to half relaxation (T(1/2)) were recorded before and after addition of 10(-6), 10(-5) and 10(-4) M racemic ketamine alone and in the presence of alpha-adrenoceptor blockade (phentolamine 10(-6) M) and beta-adrenoceptor blockade (propranolol at 10(-6) M). Ketamine had a moderate positive inotropic effect at 10(-5) M (FoC, 104% +/- 5% of baseline value; P = 0.03) and 10(-4) M (FoC, 107% +/- 11% of baseline value; P = 0.09). Racemic ketamine had a negative inotropic effect in the presence of propranolol (FoC, ketamine 10(-6) M, 77% +/- 11%; ketamine 10(-5) M, 63% +/- 16%; ketamine 10(-4) M, 62% +/- 17% of baseline; P < 0.001) but not phentolamine (FoC, ketamine at 10(-6) M, 94% +/- 6%; ketamine 10(-5) M, 96% +/- 5%; and ketamine 10(-4) M, 98% +/- 15% of baseline). Ketamine decreased T(1/2) (ketamine 10(-5) M, 94% +/- 3% of baseline value; P < 0.001 and ketamine 10(-4) M, 90% +/- 9% of baseline value; P = 0.007) but did not modify R2. In human right atrial myocardium, racemic ketamine induced a moderate positive inotropic effect and hastened isometric relaxation. In the presence of beta-adrenoceptor blockade it induced a direct negative inotropic effect.

THE INFLUENCE OF MOTOR AXON MISDIRECTION ON MUSCLE CONTRACTION FORCE IN EARLY NERVE REPAIR IN A RAT SCIATIC NERVE MODEL

We examined the influence of misdirection of regenerating motor axons toward the distal sensory Schwann tubes on the muscle contraction force in early nerve repair using a rat sciatic nerve model. At 0, 1, 2, 4 and 8 weeks after severing the tibial, peroneal and sural nerves, the proximal stump of the tibial nerve was anastomosed with the distal stumps of both the peroneal and sural nerves using tubulisation (n=10 in each of five groups). We intentionally used the distal stump of the sural nerve (a sensory nerve) to induce regeneration in motor axons from the proximal tibial nerve stump toward the distal sensory nerve stump. Twenty-four weeks after nerve repair, isometric contraction force and wet weight of the anterior tibial muscle were measured, and the numbers of regenerated myelinated axons (motor and sensory) in the distal sural and peroneal nerves were counted. The rates of sural nerve regeneration were significantly higher at weeks 0 and 1 than at the later repair times. However, muscle contraction force and muscle wet weight did not differ significantly between groups in which nerves were repaired within four weeks of severance. These results indicate that peripheral nerve repair within four weeks of severance does not influence the muscle contraction force of single muscle despite the misdirection of motor axons toward the distal sensory Schwann tubes.

Regeneration along intact nerves using nerve growth factor and ciliary neurotrophic factor.

The purpose of this investigation was to evaluate the ability of a specific growth factor combination, nerve growth factor (NGF) and ciliary neurotrophic factor (CNTF), to enhance peripheral nerve regeneration. Eight groups of eight Sprague-Dawley rats underwent repair of a nerve gap defect: Group A (immediate repair), Group B (intact nerve bridge), Group C (nerve autograft), Group D (gap in situ), Group E (NGF + CNTF), Group F (NGF), Group G (CNTF), and Group H (saline). Twelve weeks after surgery, analysis included the measurement of the isometric force of muscle contraction for the tibialis anterior muscle and tissue harvesting for both quantitative and qualitative analysis. When evaluating muscle contraction force, there was no statistically significant difference among the experimental groups receiving a growth factor injection and the normal saline control group. The hypothesis of this study was that peripheral nerve regeneration could be enhanced by the combination of NGF and CNTF. The evidence does not support this hypothesis.

Effect of acute static stretching on force, balance, reaction time, and movement time.

The purpose of the study was to investigate the effect of an acute bout of lower limb static stretching on balance, proprioception, reaction, and movement time. Sixteen subjects were tested before and after both a static stretching of the quadriceps, hamstrings, and plantar flexors or a similar duration control condition. The stretching protocol involved a 5-min cycle warm-up followed by three stretches to the point of discomfort of 45 s each with 15-s rest periods for each muscle group. Measurements included maximal voluntary isometric contraction (MVC) force of the leg extensors, static balance using a computerized wobble board, reaction and movement time of the dominant lower limb, and the ability to match 30% and 50% MVC forces with and without visual feedback. There were no significant differences in the decrease in MVC between the stretch and control conditions or in the ability to match submaximal forces. However, there was a significant (P < 0.009) decrease in balance scores with the stretch (decreasing 9.2%) compared with the control (increasing 17.3%) condition. Similarly, decreases in reaction (5.8%) and movement (5.7%) time with the control condition differed significantly (P < 0.01) from the stretch-induced increases of 4.0% and 1.9%, respectively. In conclusion, it appears that an acute bout of stretching impaired the warm-up effect achieved under control conditions with balance and reaction/movement time.