Short-term creatine supplementation does not improve muscle activation or sprint performance in humans

The purpose of this study was to examine the influence of short-term creatine (Cr) supplementation on exercise-induced transverse relaxation time (T2) and sprint performance during maximum intermittent cycling exercise using the muscle functional magnetic resonance imaging (mfMRI) technique. Twelve men were divided into a Cr supplementation group [the Cr group, taking 4 × (5 g Cr monohydrate + 2.5 g maltodextrin)/day], or a placebo supplementation group (the P group, taking 4×7.5 g maltodextrin/day). The allocation to the groups was based on cycling tests and the subjects physical characteristics, and thus was not randomized. A double-blind research design was employed for a 5-day supplementation period. mfMR images of the right thigh were collected at rest and immediately after two, five, and ten 6-s sprint bouts of maximum intermittent cycling exercise with a 30-s recovery interval between sets. Before and after supplementation, blood was taken to calculate lactate accumulation, and the muscle volume of the thigh was determined by MRI. Following supplementation, there was significant body mass gain in the Cr group (P<0.05), whereas the P group did not change. The exercise-induced T2, blood lactate levels and sprint performance were not affected by Cr supplementation in any sprint bouts. These results suggest that short-term Cr supplementation does not influence short duration repetitive sprint performance and muscle activation and/or metabolic state during sprint cycling evaluated by mfMRI of the skeletal muscle in humans.     

Exercise-induced muscle damage and the repeated bout effect: evidence for cross transfer

We examined whether a prior bout of eccentric exercise in the elbow flexors provided protection against exercise-induced muscle damage in the contralateral arm. Fifteen males (age 22.7 ± 2.1 years; height 178.6 ± 6.8 cm, mass 75.8 ± 9.3 kg) were randomly assigned to two groups who performed two bouts of 60 eccentric contractions (30°/s) separated by 2 weeks: ipsilateral (n = 7, both bouts performed in the same arm), contralateral (n = 8, one bout performed in each arm). Strength, muscle soreness and resting arm angle (RAA) were measured at baseline and at 1, 24 and 48 h post exercise. Surface electromyography was recorded during both bouts of exercise. The degree of strength loss was attenuated (p < 0.05) in the ipsilateral group after the second bout of eccentric exercise (−22 cf. −3% for bout 1 and 2 at 24 h, respectively). Strength loss following eccentric exercise was also attenuated (p < 0.05) at 24 h in the contralateral group (−30 cf. 13% for bout 1 and 2, respectively). Muscle soreness (≈34 cf 19 mm) and change in RAA (≈5 cf. 3%) were also lower following the second bout of eccentric exercise (p < 0.05), although there was no difference in the overall change in these values between groups. Median frequency (MF) was decreased by 31% between bouts, with no difference between groups. Data support observations that the repeated bout effect transfers to the opposite (untrained) limb. The similar reduction in MF between bouts for the two groups provides evidence for a centrally mediated, neural adaptation.     

How does action resist visual illusion? Uncorrected oculomotor information does not account for accurate pointing in peripersonal space

The amplitudes and signs of cutaneous reflexes are modulated during rhythmic movements of the arms and legs (during walking and arm or leg cycling for instance). This reflex modulation is frequently independent of the background muscle activity and may involve central pattern generator (CPG) circuits. The purpose of the present study was to investigate the nature and degree of coupling between the upper limbs during arm cycling, with regard to the regulation of cutaneous reflexes. Responses to electrical stimulations of the right, superficial radial nerve (five 1 ms pulses, 300 Hz) were recorded bilaterally in six arm muscles of eight participants during arm cycling involving only the limb ipsilateral to the stimulation, only the limb contralateral to the stimulation, and bilateral movement when the limbs were both in-phase and 180° out of phase. The pattern of cutaneous reflex modulation throughout the arm cycle was independent of the functional state of the limb contralateral to the recording site, irrespective of whether recordings were made ipsilateral or contralateral to the stimulation. Furthermore, cutaneous reflexes were significantly (p<0.05) modulated with arm position in only 8% of cases in which the limb containing the responding muscle was either stationary or being moved passively by the experimenter. The results show that there is relatively weak coupling between the arms with regard to the regulation of cutaneous reflexes during rhythmic, cyclical arm movements. This suggests a loose connection between the CPGs for each arm that regulate muscle activity and reflex amplitude during rhythmic movement.     

Correlation between proprioception, muscle strength, knee laxity, and dynamic standing balance in patients with chronic anterior cruciate ligament deficiency

Proprioception and muscle strength are both reported to influence single-limb stance balance in patients with chronic anterior cruciate ligament (ACL) injuries. However, the effects of these parameters on dynamic stance balance in such patients are currently unknown. This study was undertaken to ascertain whether proprioception, muscle strength, and knee laxity are correlated with dynamic standing balance in patients with ACL deficiency. Ten young men with unilateral ACL deficiency participated in this study. The mean time interval from the injury to the study was 12.8 months. Knee laxity measurements, passive re-positioning (PRP) and threshold for detection of passive motion (TTDPM) proprioception tests, quadriceps and hamstring muscle strength tests, and dynamic single-limb balance tests were performed for both injured and uninjured limbs. Significant differences between the injured and uninjured sides were observed for all test parameters. As independent variables, knee laxity, PRP proprioception, and muscle strength did not correlate with dynamic standing balance for the injured limb. However, a significant positive correlation (P < 0.05) between TTDPM proprioception and dynamic single-limb stance balance was observed for the injured limb. To improve dynamic single-limb stance balance in patients with ACL injuries, training in TTDPM proprioceptive ability is recommended as the most important initial approach for such patients.     

Similarity in the dynamics of contralateral motor overflow through increasing frequency of movement in a single limb

This study was designed to investigate the effects of increasing movement frequency of a single limb on the degree of similarity and coherence of the motor outflow in the non-active limb. Twelve young adults performed a series of unilateral hand-clapping tasks (horizontal and vertical in 25-s trials) while seated. Individuals began the movements at a frequency of 1 Hz for 5 s and were required to increase the movement frequency so as to reach their maximum movement frequency during the latter parts of the trial. Hand and finger kinematics and surface EMG of each arm were recorded. The results showed a progressive emergence of overflow muscle activity and involuntary motion in the non-active arm as the movement frequency of the unilateral action increased toward the upper frequency limits of voluntary movement. This ceiling occurred within the range of 6–7 Hz. Activity in the non-active limb emerged as the movement frequency requirements increased, irrespective of the direction of motion for the task (vertical, horizontal), hand used (preferred, non-preferred) or the auditory timing stimulus provided (metronome, no-metronome). The dynamics of the motor overflow in the non-active limb exhibited time- and frequency-dependent patterns similar to those of the active arm. Together, these results demonstrate that the high-frequency unilateral movements of one limb drives the emergence of motor outflow to the opposite limb with the motor output dynamics being produced across both limbs being progressively similar as movement speed increases.     

Association of muscle hardness with muscle tension dynamics: a physiological property

This study aimed to investigate the relationship between muscle hardness and muscle tension in terms of length–tension relationship. A frog gastrocnemius muscle sample was horizontally mounted on the base plate inside a chamber and was stretched from 100 to 150% of the pre-length, in 5% increments. After each step of muscle lengthening, electrical field stimulation for induction of tetanus was applied using platinum-plate electrodes positioned on either side of the muscle submerged in Ringer’s solution. The measurement of muscle hardness, i.e., applying perpendicular distortion, was performed whilst maintaining the plateau of passive and tetanic tension. The relationship between normalised tension and normalised muscle hardness was evaluated. The length–hardness diagram could be created from the modification with the length–tension diagram. It is noteworthy that muscle hardness was proportional to passive and total tension. Regression analysis revealed a significant correlation between muscle hardness and passive and total tension, with a significant positive slope (passive tension: r = 0.986, P < 0.001; total tension: r = 0.856, P < 0.001). In conclusion, our results suggest that muscle hardness depends on muscle tension in most ranges of muscle length in the length–tension diagram.     

Heterogeneity of muscle deoxygenation kinetics during two bouts of repeated heavy exercises

This study examines the effect of prior heavy exercise on the spatial distribution of muscle deoxygenation kinetics at the onset of heavy-intensity cycling exercise. Young untrained male adults (n = 16) performed two consecutive bouts of 6 min of high intensity cycle exercise separated by 6 min at 35 W. Muscle deoxygenation (HHb) was monitored continuously by near-infrared spectroscopy at eight sites in the quadriceps. Prior heavy exercise reduced the delay before the increase in HHb (9 ± 2 vs. 5 ± 2 s; P < 0.001). The standard deviation of TD HHb of the eight sites was decreased by the performance of prior exercise (1.1 ± 0.5 vs. 0.8 ± 0.4 s; P < 0.05). The transient decrease in HHb during the first 10 s of exercise was less during the second bout than during the first bout (0.6 ± 0.6 vs. 0.3 ± 0.3 A.U.; P < 0.01). The standard deviation of this decrease was also reduced by prior exercise (0.5 ± 0.3 vs. 0.3 ± 0.2 A.U.; P < 0.01). Lastly, prior exercise decreased significantly the standard deviation of the HHb rise during the time period corresponding to the pulmonary [(V)\dot] \dot{V} O₂ slow component. These results indicate that prior heavy exercise reduced the spatial heterogeneity of muscle deoxygenation kinetics at the early onset of heavy exercise and during the development of the pulmonary [(V)\dot] \dot{V} O₂ slow component. It indicates that the distribution of the [(V)\dot] \dot{V} O₂/O₂ delivery ratio within muscle was improved by the performance of a prior exercise.     

Unchanged muscle fiber conduction velocity relates to mild acidosis during exhaustive bicycling

Muscle fiber conduction velocity (MFCV) has often been shown to decrease during standardized fatiguing isometric contractions. However, several studies have indicated that the MFCV may remain constant during fatiguing dynamic exercise. It was investigated if these observations can be related to the absence of a large decrease in pH and if MFCV can be considered as a good indicator of acidosis, also during dynamic bicycle exercise. High-density surface electromyography (HDsEMG) was combined with read-outs of muscle energetics recorded by in vivo ³¹P magnetic resonance spectroscopy (MRS). Measurements were performed during serial exhausting bouts of bicycle exercise at three different workloads. The HDsEMG recordings revealed a small and incoherent variation of MFCV during all high-intensity exercise bouts. ³¹P MRS spectra revealed a moderate decrease in pH at the end of exercise (~0.3 units down to 6.8) and a rapid ancillary drop to pH 6.5 during recovery 30 s post-exercise. This additional degree of acidification caused a significant decrease in MFCV during cycling immediately after the rest period. From the data a significant correlation between MFCV and [H⁺] ([H⁺] = 10^−pH) was calculated (p < 0.001, Pearson’s R = −0.87). Our results confirmed the previous observations of MFCV remaining constant during fatiguing dynamic exercise. A constant MFCV is in line with a low degree of acidification, considering the presence of a correlation between pH and MFCV after further increasing acidification.     

Optimum loading for maximizing muscle power output: the effect of training history

Although the effect of external load on the mechanical output of individual muscle has been well documented, the literature still provides conflicting evidence regarding whether the optimum loading (L_opt) for exerting the maximum muscle power output (MPO) could be different for individuals with different levels of strength and power. The aim of this study was to explore the effect of training history on L_opt that maximizes MPO during the 6-s maximal cycling sprint test. Forty healthy young males (strength-and speed-trained athletes, and physically active and sedentary non-athletes) were tested on maximum strength, and on peak MPO when loaded 5–12% of body weight (BW). As expected, the strength trained and sedentary participants, respectively, revealed the highest and lowest strengths and MPO (p < 0.001). However, the main finding was a significant across-group difference in L_opt (p < 0.001) revealing the values 9.7% (for strength trained), 9.2% (speed trained), 8.7% (active), and 8.0% of BW (sedentary individuals). This suggests that the effects of external loading on maximum MPO in complex functional movements could be training history dependent. In addition to revealing a sensitivity of the 6-s maximal cycling sprint tests (and, perhaps, other maximum cycling tests), the results suggest that the external loading in routine MPO tests should not be solely adjusted to a fixed percentage of subject’s BW (as routinely done in standard tests), but also to their training history. The same phenomenon remains to be evaluated in a number of other routine tests of MPO and other maximum performance tasks.     

Effect of cycling on oxygenation of relaxed neck/shoulder muscles in women with and without chronic pain

Work-related neck/shoulder muscle pain has been associated with increased anaerobic muscle metabolism. Thus, interventions to enhance oxygenation of painful muscles seem relevant. While cycling with relaxed shoulders has been shown to result in acute neck/shoulder muscle pain reduction, the effect on tissue oxygenation remains unknown. The aim of the present study was to investigate tissue oxygenation of the passive trapezius muscle during and after cycling in female workers with (MYA) and without (CON) trapezius myalgia. Eligible participants (n = 17 MYA, n = 8 CON) performed 20 min sub-maximal cycling in an upright position with relaxed shoulders. Near-infrared spectroscopy was used to measure trapezius muscle oxygenation during and 2 min after the cycling period. For both MYA and CON, oxygenation of the passive trapezius increased in a linear fashion over time, to values ~5 μM above baseline at the end of the cycling period, with no significant group difference (CON 5.2, MYA 4.9 μM). Two min after termination of exercise, oxygenation was increased further in both groups, but significantly more in CON (8.8 μM) than in MYA (7.0 μM) (P = 0.05). In conclusion, cycling increases oxygenation of resting neck/shoulder muscles in women with and without trapezius myalgia, indicating acute positive effects of either neural or humoral factors on vascular beds of distant relaxed muscles. Although this beneficial response was observed in both groups, the post-exercise response was lower in women with trapezius myalgia.     

The respiratory response to passive and active arm movements is enhanced in delayed onset muscle soreness

We previously reported that ventilatory response at the onset of light leg exercise was augmented in delayed onset muscle soreness (DOMS) after eccentric exercise (ECC) utilizing the leg. In this study, we examined whether the same result would appear in light exercise in which an arm with DOMS was utilized. Eleven subjects performed ECC using one arm, and we measured ventilatory responses to a 20-s single-arm extension–flexion exercise and to passive movement (PAS) before and 2 days after ECC (D2). We found that ventilatory response to both the exercise and PAS in which all subjects perceived DOMS was augmented at D2. It was concluded that initial hyperpnea, which occurred during arm exercise in DOMS, was enhanced, and from examining the result of PAS, enhanced initial exercise hyperpnea may be due in part to an exaggerated peripheral neural reflex.     

The impact of obesity on skeletal muscle architecture in untrained young vs. old women

It is unknown whether loading of the lower limbs through additional storage of fat mass as evident in obesity would promote muscular adaptations similar to those seen with resistance exercise. It is also unclear whether ageing modulates any such adjustments. This study aimed to examine the relationships between adiposity, ageing and skeletal muscle size and architecture. A total of 100 untrained healthy women were categorised by age into young (Y) (mean ± SD: 26.7 ± 9.4 years) vs. old (O) (65.1 ± 7.2 years) and body mass index (BMI) classification (underweight, normal weight, overweight and obese). Participants were assessed for body fat using dual energy x‐ray absorptiometry, and for gastrocnemius medialis (GM) muscle architecture (skeletal muscle fascicle pennation angle and length) and size [GM muscle volume and physiological cross‐sectional area (PCSA)] using B‐mode ultrasonography. GM fascicle pennation angle (FPA) in the obese Y females was 25% greater than underweight (P = 0.001) and 25% greater than normal weight (P = 0.001) individuals, while O females had 32 and 22% greater FPA than their underweight (P = 0.008) and normal weight (P = 0.003) counterparts. Furthermore, FPA correlated with body mass in both Y and O females (Y r = 0.303; P < 0.001; O r = 0.223; P = 0.001), yet no age‐related differences in the slope or r‐values were observed (P > 0.05). Both GM muscle volume (P = 0.003) and PCSA (P = 0.004) exhibited significant age × BMI interactions. In addition, muscle volume and PCSA correlated with BMI, body mass and fat mass. Interestingly, ageing reduced both the degree of association in these correlations (P < 0.05) and the slope of the regressions (P < 0.05). Our findings partly support our hypotheses in that obesity‐associated changes in GM PCSA and volume differed between the young and old. The younger GM muscle adapted to the loading induced by high levels of body mass, adiposity and BMI by increasing its volume and increasing its pennation angle, ultimately enabling it to produce higher maximum torque. Such an adaptation to increased loading did not occur in the older GM muscle. Nonetheless, the older GM muscle FPA increased to a similar extent to that seen in young GM muscle, an effect which partly explains the relatively enhanced absolute maximum torque observed in obese older females.     

10 or 30-s sprint interval training bouts enhance both aerobic and anaerobic performance

We assessed whether 10-s sprint interval training (SIT) bouts with 2 or 4 min recovery periods can improve aerobic and anaerobic performance. Subjects (n = 48) were assigned to one of four groups [exercise time (s):recovery time (min)]: (1) 30:4, (2) 10:4, (3) 10:2 or (4) control (no training). Training was cycling 3 week⁻¹ for 2 weeks (starting with 4 bouts session⁻¹, increasing 1 bout every 2 sessions, 6 total). Pre- and post-training measures included: VO_2max, 5-km time trial (TT), and a 30-s Wingate test. All groups were similar pre-training and the control group did not change over time. The 10-s groups trained at a higher intensity demonstrated by greater (P < 0.05) reproducibility of peak (10:4 = 96%; 10:2 = 95% vs. 30:4 = 89%), average (10:4 = 84%; 10:2 = 82% vs. 30:4 = 58%), and minimum power (10:4 = 73%; 10:2 = 69%; vs. 30:4 = 40%) within each session while the 30:4 group performed ~2X (P < 0.05) the total work session⁻¹ (83–124 kJ, 4–6 bouts) versus 10:4 (38–58 kJ); 10:2 (39–59 kJ). Training increased TT performance (P < 0.05) in the 30:4 (5.2%), 10:4 (3.5%), and 10:2 (3.0%) groups. VO_2max increased in the 30:4 (9.3%) and 10:4 (9.2%), but not the 10:2 group. Wingate peak power kg⁻¹ increased (P < 0.05) in the 30:4 (9.5%), 10:4 (8.5%), and 10:2 (4.2%). Average Wingate power kg⁻¹ increased (P < 0.05) in the 30:4 (12.1%) and 10:4 (6.5%) groups. These data indicate that 10-s (with either 2 or 4 min recovery) and 30-s SIT bouts are effective for increasing anaerobic and aerobic performance.     

Semimembranosus muscle displacement is associated with movement of the superficial fascia: An in vivo ultrasound investigation

The deep fascia enveloping the skeletal muscle has been shown to contribute to the mechanics of the locomotor system. However, less is known about the role of the superficial fascia (SF). This study aimed to describe the potential interaction between the Hamstring muscles and the SF. Local movement of the dorsal thigh's soft tissue was imposed making use of myofascial force transmission effects across the knee joint: In eleven healthy individuals (26.8 ± 4.3 years, six males), an isokinetic dynamometer moved the ankle into maximal passive dorsal extension (knee extended). Due to the morphological continuity between the gastrocnemius and the Hamstrings, stretching the calf led to soft tissue displacements in the dorsal thigh. Ultrasound recordings were made to dynamically visualize (a) the semimembranosus muscle and (b) the superficial fascia. Differences in and associations between horizontal movement amplitudes of the two structures, quantified via cross-correlation analyses, were calculated by means of the Mann–Whitney U test and Kendal's tau test, respectively. Mean horizontal movement was significantly higher in the muscle (5.70 mm) than in the SF (0.72 mm, p < 0.001, r = 0.82). However, a strong correlation between the tissue displacements in both locations was detected (p < 0.001, r = 0.91). A Direct mechanical relationship may exist between the SF and the skeletal muscle. Deep pathologies or altered muscle stiffness could thus have long-term consequences for rather superficial structures and vice versa.     

Muscle damage responses of the elbow flexors to four maximal eccentric exercise bouts performed every 4 weeks

Since little is known about the repeated bout effect of more than two eccentric exercise bouts, this study compared muscle damage responses among four exercise bouts. Fifteen young (21.8 ± 1.9 years) men performed four bouts of 30 maximal isokinetic eccentric contractions of the elbow flexors every 4 weeks. Maximal voluntary elbow flexion isometric and concentric strength, range of motion at the elbow joint (ROM), upper arm circumference, blood markers of muscle damage, and muscle soreness were measured before and up to 120 h following each bout. Changes in all measures following the second to fourth bouts were significantly (P < 0.05) smaller than those after the first bout. The decreases in strength and ROM immediately after the fourth bout were significantly (P < 0.05) smaller than other bouts. It is concluded that the first bout confers the greatest adaptation, but further adaptation is induced when the exercise is repeated more than three times.     

Lower limb compression garment improves recovery from exercise-induced muscle damage in young, active females

This study aimed to investigate the efficacy of lower limb compression as a recovery strategy following exercise-induced muscle damage (EIMD). Seventeen female volunteers completed 10 × 10 plyometric drop jumps from a 0.6-m box to induce muscle damage. Participants were randomly allocated to a passive recovery (n = 9) or a compression treatment (n = 8) group. Treatment group volunteers wore full leg compression stockings for 12 h immediately following damaging exercise. Passive recovery group participants had no intervention. Indirect indices of muscle damage (muscle soreness, creatine kinase activity, knee extensor concentric strength, and vertical jump performance) were assessed prior to and 1, 24, 48, 72, and 96 h following plyometric exercise. Plyometric exercise had a significant effect (p ≤ 0.05) on all indices of muscle damage. The compression treatment reduced decrements in countermovement jump performance (passive recovery 88.1 ± 2.8% vs. treatment 95.2 ± 2.9% of pre-exercise), squat jump performance (82.3 ± 1.9% vs. 94.5 ± 2%), and knee extensor strength loss (81.6 ± 3% vs. 93 ± 3.2%), and reduced muscle soreness (4.0 ± 0.23 vs. 2.4 ± 0.24), but had no significant effect on creatine kinase activity. The results indicate that compression clothing is an effective recovery strategy following exercise-induced muscle damage.     

Suppression of soleus H-reflex amplitude is graded with frequency of rhythmic arm cycling

In humans, rhythmic arm cycling has been shown to significantly suppress the soleus H-reflex amplitude in stationary legs. The specific nature of the relationship between frequency of arm cycling and H-reflex modulation in the legs has not been explored. We speculated that the effect of arm cycling on reflexes in leg muscles is related to the neural control of arm movement; therefore, we hypothesized that a graded increase in arm cycling frequency would produce a graded suppression of the soleus H-reflex amplitude. We also hypothesized that a threshold frequency of arm cycling would be identified at which the H-reflex amplitude significantly differed from static control trials (i.e., the arms were stationary). Soleus H-reflexes were evoked in stationary legs with tibial nerve stimulation during both control and rhythmic arm cycling (0.03–2.0 Hz) trials. The results show a significant inverse linear relation between arm cycling frequency and soleus H-reflex amplitude (P < 0.05). Soleus H-reflex amplitude significantly differed from control at an average threshold cycling frequency of 0.8 Hz. The results demonstrate that increased frequency of upper limb movement increases the intensity of interlimb influences on the neural activity in stationary legs. Further, a minimum threshold frequency of arm cycling is required to produce a significant effect. This suggests that achieving a threshold frequency of rhythmic arm movement may be important to incorporate in rehabilitation strategies to engage the appropriate interlimb neural pathways.     

被动运动对脊髓损伤大鼠后肢运动功能及骨骼肌的影响

目的　观察被动运动促进脊髓损伤（Spinal cord injury, SCI）大鼠后肢运动功能恢复和改善骨骼肌萎缩的影响;探讨脑源性神经营养因子（BDNF）对被动运动促进功能恢复和延缓肌萎缩的作用。 方法　将36只健康成年雌性SD大鼠随机分假手术组、对照组（未行运动）,被动运动组（损伤1周后开始被动运动,共4 周）。采用改良的Allen’s法制备SCI模型。术后1 d和1、2、3、4 周通过大鼠Basso-Beattie-Bresnahan(BBB)行为学评分检测各组大鼠的运动功能;术后5周,采用HE染色比较各组大鼠脊髓组织病理变化,观察大鼠后肢腓肠肌的横断面积、直径和形态变化。测量腓肠肌湿重、体重和肌湿重/体重,评价肌萎缩情况;采用Western blots检测腓肠肌中BDNF的表达变化。 结果　被动运动组运动功能明显高于对照组（P<0.05）。损伤5周后,对照组和被动运动组的脊髓组织失去正常形态,神经元数量减少,损伤区大量空洞形成,而被动运动组的变化较对照组轻。对照组腓肠肌湿重、肌湿重/体重、横断面积和直径下降,被动运动组改善上述肌萎缩情况（P<0.05）。与假手术组相比,对照组和被动运动组BDNF表达量增加（P<0.05）,其中被动运动组高于对照组（P<0.05）。 结论　被动运动可能是通过增加SCI后BDNF表达促进损伤后运动功能的恢复,并能有效改善失神经性肌萎缩。     

Mechanical properties of passive rat muscle during sinusoidal stretching

The dynamic passive response of the left gastrocnemius medialis muscle of thirty male Wistar rats was studied as a function of muscle dimensions and absolute and relative amount of connective tissue. Values of the absolute active and passive length-force curves (active force, passive force, active working range) correlated well (coefficients of correlation in a range of 0.62–0.92) with morphological variables (such as muscle optimum length, mean muscle fibre optimum length, physiological cross section, muscle weight and amount of intramuscular connective tissue). To eliminate dimensional effects the active and passive length-force curves were normalized taking maximal active twitch force and muscle optimum length as reference values (100%). The width of the normalized active length-force curve (relative active working range) was correlated negatively with muscle weight, muscle optimum length and physiological cross section. Relative amount of connective tissue and passive tension at optimum length (both independent of muscle dimensions) were positively correlated, indicating that passive muscles are stiffer when relative amount of intramuscular connective tissue is higher. Sinusoidal movements with several amplitudes and frequencies of movement were imposed on the passive gastrocnemius medialis muscle over a range of muscle lengths. In accordance with the approximately exponential increase of static passive muscle force with length, muscle length has a large influence on the shape and magnitude of the hysteresis diagrams resulting from sinusoidal movements: the value of all variables selected increases approximately exponentially with muscle length with the exception of the value of loss tangent, a factor indicating the amount of energy dissipated during each cycle relative to the amount of energy stored and released elastically. Velocity of movement has only minor influence on variables of the hysteresis diagrams as is shown by changing the frequency of movement. As loss tangent and relative amount of connective tissue did not vary with muscle dimensions in the muscles studied, it is likely that material properties of the components causing passive resistance were similar in these muscles.     

Strategies for the integration of posture and movement during reaching in the cat

We have examined the relationship between the movement and the anticipatory postural adjustments (APAs) that precede that movement during a reaching task in the cat. We recorded ground reaction forces in all 3 planes from all 4 limbs as well as electromyographic (EMG) activity from limb and axial muscles. The reaching movement was always preceded by an APA that was characterized by a loading of the reaching forelimb and an unloading of the support forelimb. This loading of the reaching forelimb was preceded, and accompanied, by increased activity in shoulder and limb extensor muscles of the reaching limb; extensor muscle activity in the supporting limb was simultaneously decreased. An important finding from this study was that the onset of the APA and of the movement was temporally decoupled. Analyses of the onset of EMG activity showed that most of the muscles that we recorded could be classified as either related to the APA or related to the movement. These results support the idea of distributed, and perhaps independent, systems for the execution of the APA and of the prime movement. There was also postural activity in the supporting limb during the movement. Analysis of this activity, which is also anticipatory in nature, suggests that it was tightly linked to the movement. We suggest that this postural response is signaled as part of the command for movement. Some muscles, particularly the extensors of the reaching limb, received convergent input from the command signals for the APA and for the movement.