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The extractive foraging behavior in aye-ayes (Daubentonia madagascariensis) is unique among primates and likely has led to selection for a specialized jaw adductor musculature. Although this musculature has previously been examined in a subadult, until now, no one has reported the fascicle length, weight, and physiological cross-sectional area (PCSA) for these muscles in an adult aye-aye specimen. For the present study, we dissected an adult wild-born aye-aye from the Tsimbazaza Botanical and Zoological Park, Antananarivo, Madagascar. The aye-aye follows the general strepsirrhine pattern in its overall jaw adductor muscle anatomy, but has very large muscles and PCSA relative to body size. Fascicle length is also relatively great, but not nearly as much as in the juvenile aye-aye previously dissected. Perhaps chewing muscle fascicles begin relatively long, but shorten through use and growth as connective tissue sheets expand and allow for pinnation and increased PCSA. Alternately, it may be that aye-ayes develop fascicular adaptation to wide gapes early in ontogeny, only to increase PCSA through later development into adulthood. The functional demands related to their distinctive manner of extractive foraging are likely responsible for the great PCSA in the jaw adductor muscles of the adult aye-aye. It may be that great jaw adductor PCSA in the adult, as compared to the juvenile, is a means of increasing foraging efficiency in the absence of parental assistance. Anat Rec, 297:308–316, 2014. V C 2013 Wiley Periodicals, Inc.

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

This study aimed to clarify whether resistance training-induced changes in muscle architecture are homogeneous among the quadriceps and over different regions within each muscle. Eleven recreationally active men (27 ± 2 years) completed a 12-week resistance training program for knee extensors. Before and after the intervention, muscle thicknesses, fascicle lengths, and pennation angles of the four muscles (vastus lateralis, vastus medialis, vastus intermedius, rectus femoris) in several regions (2–4 regions per each muscle) were measured using ultrasonography. Anatomical cross-sectional areas (ACSAs) at the same positions as the ultrasound measurements were determined from magnetic resonance images. Relative increases in the ACSA, muscle thickness, and pennation angle of the rectus femoris were significantly greater than those of the vasti. Relative increases in the ACSAs of the vastus lateralis and rectus femoris were significantly greater in the distal than in the proximal region, and those in the muscle thickness and pennation angle of the vastus intermedius were significantly greater in the medial than in the lateral region. Fascicle lengths did not change in any muscles. The interrelations between muscle thickness and pennation angle remained unchanged after the intervention, with a significant association between the relative changes of the two variables. The current results indicate that (1) hypertrophy of the quadriceps femoris is associated with a proportional increase in pennation angle but not necessarily in fascicle length, and (2) training-induced changes in muscle size and pennation do not evenly occur among the quadriceps, along or across a muscle.

Introduction: Changes in muscle architecture induced by eccentric knee extensor training remain unclear, as well the adaptive responses of synergistic knee extensor muscles with different geometrical designs. Methods: Ultrasonography images were taken from rectus femoris (RF) and vastus lateralis (VL) of 20 male volunteers before and after a non-training control period of 4 weeks, and additional evaluations were performed after 4, 8, and 12 weeks of isokinetic eccentric training. Results: RF and VL had significant changes in muscle architecture within the first 4 training weeks, and the adaptive response throughout the intervention was similar. Muscle thickness increased by around 7–10%, fascicle length increased 17–19%, and pennation angle was unchanged. Conclusions: Increased muscle thickness due to eccentric training was related to increased fascicle length and not to pennation angle changes. Although RF and VL have a different fascicular geometry, they had similar morphological adaptations to eccentric training. Muscle Nerve 48: 498–506, 2013

Ankle plantar flexor muscles support and propel the body in the stance phase of locomotion. Besides the triceps surae, flexor hallucis longus muscle (FHL) may also contribute to this role, but very few in vivo studies have examined FHL function during walking. Here, we investigated FHL fascicle behavior at different walking speeds. Ten healthy males walked overground at three different speeds while FHL fascicle length changes were recorded with ultrasound and muscle activity was recorded with surface electromyography (EMG). Fascicle length at heel strike at toe off and at peak EMG activity did not change with speed. Range of FHL fascicle length change (3.5-4.5 and 1.9-2.9 mm on average in stance and push-off phase, respectively), as well as minimum (53.5-54.9 and 53.8-55.7 mm) and maximum (58-58.4 and 56.8-57.7 mm) fascicle length did not change with speed in the stance or push-off phase. Mean fascicle velocity did not change in the stance phase, but increased significantly in the push-off phase between slow and fast walking speeds (P=.021). EMG activity increased significantly in both phases from slow to preferred and preferred to fast speed (P

Most common preventive eccentric-based exercises, such as Nordic hamstring do not include any hip flexion. So, the elongation stress reached is lower than during the late swing phase of sprinting. The aim of this study was to assess the evolution of hamstring architectural (fascicle length and pennation angle) and functional (concentric and eccentric optimum angles and concentric and eccentric peak torques) parameters following a 3-week eccentric resistance program performed at long (LML) vs. short muscle length (SML). Both groups performed eight sessions of 3-5 × 8 slow maximal eccentric knee extensions on an isokinetic dynamometer: the SML group at 0° and the LML group at 80° of hip flexion. Architectural parameters were measured using ultrasound imaging and functional parameters using the isokinetic dynamometer. The fascicle length increased by 4.9% (p < 0.01, medium effect size) in the SML and by 9.3% (p < 0.001, large effect size) in the LML group. The pennation angle did not change (p = 0.83) in the SML and tended to decrease by 0.7° (p = 0.09, small effect size) in the LML group. The concentric optimum angle tended to decrease by 8.8° (p = 0.09, medium effect size) in the SML and by 17.3° (p < 0.01, large effect size) in the LML group. The eccentric optimum angle did not change (p = 0.19, small effect size) in the SML and tended to decrease by 10.7° (p = 0.06, medium effect size) in the LML group. The concentric peak torque did not change in the SML (p = 0.37) and the LML (p = 0.23) groups, whereas eccentric peak torque increased by 12.9% (p < 0.01, small effect size) and 17.9% (p < 0.001, small effect size) in the SML and the LML group, respectively. No group-by-time interaction was found for any parameters. A correlation was found between the training-induced change in fascicle length and the change in concentric optimum angle (r = -0.57, p < 0.01). These results suggest that performing eccentric exercises lead to several architectural and functional adaptations. However, further investigations are required to confirm the hypothesis that performing eccentric exercises at LML may lead to greater adaptations than a similar training performed at SML.

Background/Aim - To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femoris long head (BFlh) fascicle length on the risk of a future hamstring strain injury (HSI). Methods - Elite soccer players (n=152) from eight different teams participated. Eccentric knee flexor strength during the Nordic hamstring exercise and BFlh fascicle length were assessed at the beginning of pre-season. The occurrences of a HSI following this were recorded by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data. Results - Twenty-seven new HSIs were reported. Eccentric knee flexor strength below 337N (RR = 4.4; 95% CI = 1.1 to 17.5) and BFlh fascicles shorter than 10.56cm (RR = 4.1; 95% CI=1.9 to 8.7) significantly increased the risk of a subsequent HSI. Multivariate logistic regression revealed significant effects when combinations of age, previous history of HSI, eccentric knee flexor strength and BFlh fascicle length were explored. From these analyses the likelihood of a future HSI in older athletes or those with a previous HSI history was reduced if high levels of eccentric knee flexor strength and longer BFlh fascicles were present. Conclusions - The presence of short BFlh fascicles and low levels of eccentric strength in elite soccer players increase the risk of a future HSI. The greater risk of a future HSI in older players or those with a previous HSI is reduced when they possess longer BFlh fascicles and high levels of eccentric strength.

Purpose:To employ cluster analysis to assess if cyclists would opt for different strategies in terms of neuromuscular patterns when pedaling at the power output of their second ventilatory threshold (POVT2) compared with cycling at their maximal power output (POMAX).Methods:Twenty athletes performed an incremental cycling test to determine their power output (POMAX and POVT2; first session), and pedal forces, muscle activation, muscle–tendon unit length, and vastus lateralis architecture (fascicle length, pennation angle, and muscle thickness) were recorded (second session) in POMAX and POVT2. Athletes were assigned to 2 clusters based on the behavior of outcome variables at POVT2 and POMAX using cluster analysis.Results:Clusters 1 (n = 14) and 2 (n = 6) showed similar power output and oxygen uptake. Cluster 1 presented larger increases in pedal force and knee power than cluster 2, without differences for the index of effectiveness. Cluster 1 presented less variation in knee angle, muscle–tendon unit length, pennation angle, and tendon length than cluster 2. However, clusters 1 and 2 showed similar muscle thickness, fascicle length, and muscle activation. When cycling at POVT2 vs POMAX, cyclists could opt for keeping a constant knee power and pedal-force production, associated with an increase in tendon excursion and a constant fascicle length.Conclusions:Increases in power output lead to greater variations in knee angle, muscle–tendon unit length, tendon length, and pennation angle of vastus lateralis for a similar knee-extensor activation and smaller pedal-force changes in cyclists from cluster 2 than in cluster 1.

Purpose: This study aimed to determine whether limbs with a history of anterior cruciate ligament (ACL) injury reconstructed from the semitendinosus display different biceps femoris long head (BFlh) architecture and eccentric strength, assessed during the Nordic hamstring exercise, compared with the contralateral uninjured limb. Methods: The architectural characteristics of the BFlh were assessed at rest and at 25% of a maximal voluntary isometric contraction (MVIC) in the control group (n = 52) and in the group who had previous ACL injury (n = 15) using two-dimensional ultrasonography. Eccentric knee flexor strength was assessed during the Nordic hamstring exercise. Results: Fascicle length was shorter (P = 0.001; d range, 0.90–1.31) and pennation angle (P range, 0.001–0.006; d range, 0.87–0.93) was greater in the BFlh of the ACL-injured limb compared with those in the contralateral uninjured limb at rest and during a 25% MVIC. Eccentric strength was lower in the ACL-injured limb when compared with the contralateral uninjured limb. Fascicle length, MVIC, and eccentric strength were not different between the left and right limb in the control group. Conclusions: Limbs with a history of ACL injury reconstructed from the semitendinosus have shorter fascicles and greater pennation angles in the BFlh compared with those of the contralateral uninjured side. Eccentric strength during the Nordic hamstring exercise of the ACL-injured limb is significantly lower than that of the contralateral side. These findings have implications for ACL rehabilitation and hamstring injury prevention practices, which should consider altered architectural characteristics.

The purpose of this research was (a) to examine the performance changes that occur in elite female softball players during 20 weeks of softball training (that included 14 weeks of periodized resistance training [RT]) and (b) to examine the relationship between percent change (%change) in muscle architecture variables and %change in strength, speed, and change of direction performance. Ten female softball players (age = 18.1 ± 1.6 years, height = 166.5 ± 8.9 cm, weight = 72.4 ± 10.8 kg) from a state Australian Institute of Sport softball team were tested for maximal lower-body strength using a 3 repetition maximum for a predicted 1 repetition maximum (1RM) and peak force, peak velocity (PV), and peak power (PP) were measured during jump squats (JS) unloaded and loaded. In addition, the first base (1B) and the second base (2B) sprint performance, change of direction (505) on dominant (D) and nondominant (ND) sides, aerobic capacity, and muscle architecture characteristics of vastus lateralis (VL) including muscle thickness (MT), fascicle length (FL), and pennation angle (θp) were examined. The testing sessions occurred pre, mid, and post training (total 20 week pre- and in-season training period). Changes over time were analyzed by repeated-measures analysis of variance. The relationship between %change in muscle architecture variables and strength, speed, and change of direction variables from pre to post were assessed by Pearson product-moment correlation coefficient. Significant improvements in PV and PP occurred at all JS loads pre- to mid-testing and pre- to post-testing. Significant increases occurred pre-post in absolute 1RM, relative 1RM, 505 ND, and 2B sprint. The strongest relationships were found between %change in VL MT and 1B sprint (r = -0.80, p = 0.06), %change in VL FL and 2B sprint (r = -0.835, p = 0.02), and %change in relative 1RM and 505 D (r = -0.70, p = 0.04). In conclusion, gains in strength, power, and performance can occur during the season in elite softball players who are also engaged in a periodized RT program. Furthermore, changes in performance measures are associated with changes in muscle architecture.

The purpose of this study was to understand the detailed architectural properties of the human hamstring muscles. The long (BFlh) and short (BFsh) head of biceps femoris, semimembranosus (SM) and semitendinosus (ST) muscles were dissected and removed from their origins in eight cadaveric specimens (age 67.8±4.3 years). Mean fiber length, sarcomere length, physiological cross-section area and pennation angle were measured. These data were then used to calculate a similarity index (δ) between pairs of muscles. The results indicated moderate similarity between BFlh and BFsh (δ=0.54) and between BFlh and SM (δ=0.35). In contrast, similarity was low between SM and ST (δ=0.98) and between BFlh and SM (δ=1.17). The fascicle length/muscle length ratio was higher for the ST (0.58) and BFsh (0.50) compared with the BFlh (0.27) and SM (0.22). There were, however, high inter-correlations between individual muscle architecture values, especially for muscle thickness and fascicle length data sets. Prediction of the whole hamstring architecture was achieved by combining data from all four muscles. These data show different designs of the hamstring muscles, especially between the SM and ST (medial) and BFlh and BFsh (lateral) muscles. Modeling the hamstrings as one muscle group by assuming uniform inter-muscular architecture yields less accurate representation of human hamstring muscle function.

In this study, the relationship between musculoskeletal architecture of the lateral gastrocnemius muscle and gait velocity in elderly individuals was investigated using ultrasonography and standardized tests of physical performance in 20 older adult males. Musculoskeletal architecture parameters included moment arm, fascicle length, pennation angle, and muscle thickness. The Six Minute Walk Test (6MIN) and Four Metre Walk Velocity Test (4METRE) were used to determine preferred and maximum gait velocity, respectively. Only weak correlations were found for all 20 subjects taken together. After subjects were separated into faster and slower subgroups by preferred velocity using cluster analysis; however, a strong correlation was found between plantarflexion moment arm and 6MIN velocity in the slower group (R(2)=0.669, p=0.004). Examination of subgroup differences revealed that the slow subgroup was significantly older than the fast subgroup (p=0.034), and had average body mass (p=0.021) and body mass index (p=0.011) that were significantly greater. The strength of the correlation between plantarflexion moment arm and 6MIN velocity found for slower subjects is much greater than those previously reported for correlations between ankle strength or power and walking velocity. Further investigation is necessary to determine if a link exists between plantarflexor moment arm and gait velocity in older and heavier adults.

To establish the effect of tendon vibration (TV) on steady submaximal strength and static balance control, 29 women performed isometric plantarflexions at 10, 20, 30 and 50% of MVC and postural tasks of increasing difficulty (Normal Quiet Stance, NQS, Sharpened Tandem Stance and One Leg Stance) with vibrators (80 Hz) applied to the Achilles tendon. Both tasks were performed under four conditions (10 s each): eyes open, eyes closed, eyes closed with TV, eyes open with TV. During the isometric tasks, the application of TV increased the plantarflexion torque at 20 and 30% of MVC, accompanied by a greater (p

Dynamic stretching is commonly used in warm-up routines for athletic activities. Even though several positive effects of dynamic stretching on athletic performance have been reported, the effects on the muscle-tendon unit (MTU) itself are still unclear. The objective of this study is to determine the effects of dynamic stretching on the ankle plantar flexor muscle-tendon properties by use of ultrasonography. Twenty healthy male subjects participated in the present study. The subjects were asked to engage in dynamic stretching of plantar flexors for 30 s and to repeat for 5 sets. Ankle dorsiflexion ROM was measured before and after the dynamic stretching. Changes in the displacement of the myotendinous junction (MTJ), pennation angle, and fascicle length were also determined by using ultrasonography. Ankle dorsiflexion ROM increased significantly after the dynamic stretching (p 0.0001). A significant distal displacement of the MTJ was observed until the second stretching set (p 0.001) with no significant changes thereafter. Pennation angle, and fascicle length were unaffected by the dynamic stretching. Dynamic stretching was shown to be effective in increasing ankle joint flexibility. Outcomes that could have indicated changes in muscle tissue (such as the pennation angle and fascicle length) were unaltered. However, a significant displacement of the MTJ was found, indicating some change in the tendon tissues. Therefore, dynamic stretching of the plantar flexors was considered an effective means of lengthening the tendon tissues.

Kannas, TM, Kellis, E, and Amiridis, IG. Biomechanical differences between incline and plane hopping. J Strength Cond Res 25(12): 3334-3341, 2011-The need for the generation of higher joint power output during performance of dynamic activities led us to investigate the force-length relationship of the plantar flexors during consecutive stretch-shortening cycles of hopping. The hypothesis of this study was that hopping (consecutive jumps with the knee as straight as possible) on an inclined (15°) surface might lead to a better jumping performance compared with hopping on a plane surface (0°). Twelve active men performed 3 sets of 10 consecutive hops on both an incline and plane surface. Ground reaction forces; ankle and knee joint kinematics; electromyographic (EMG) activity from the medial gastrocnemius (MG), soleus (Sol) and tibialis anterior (TA); and architectural data from the MG were recorded. The results showed that participants jumped significantly higher (p0.05) when hopping on an inclined surface (30.32 ± 8.18 cm) compared with hopping on a plane surface (27.52 ± 4.97 cm). No differences in temporal characteristics between the 2 types of jumps were observed. Incline hopping induced significantly greater ankle dorsiflexion and knee extension at takeoff compared with plane hopping (p0.05). The fascicle length of the MG was greater at initial contact with the ground during incline hopping (p0.05). Moreover, the EMG activities of Sol and TA during the propulsion phase were significantly higher during incline compared with that during plane hopping (p0.05). It does not seem unreasonable to suggest that, if the aim of hopping plyometrics is to improve plantar flexor explosivity, incline hopping might be a more effective exercise than hopping on a plane surface.

Summary. Recent advances in imaging have enhanced our understanding of the morphological adaptations of muscle in response to disease and altered use. Adaptation in muscle morphology has been linked to changes in muscle strength. To date, no studies have compared muscle morphology and strength in young children with haemophilia to that of typically developing children. This study explored differences in muscle strength and morphology between typically developing and age and size-matched boys aged 6–12 years with haemophilia and a history of recurrent haemorrhage in the ankle joint. Maximum muscle strength of the knee flexors (KF), extensors (KE), ankle dorsi (ADF) and plantar flexors (APF) was measured in 19 typically developing boys (Group 1) and 19 boys with haemophilia (Group 2). Ultrasound images of vastus lateralis (VL) and lateral gastrocnemius (LG) were recorded to determine muscle cross-sectional area (CSA), thickness, width, fascicle length and pennation angle. Muscle strength of the KE, ADF and APF were significantly (P

The aim of this study was to examine the effects of incline plyometrics training on muscle activation and architecture during vertical jumping and maximum strength. Twenty male participants were divided in two training groups which followed after a 4 week training program. The incline plyometrics group (n = 10) trained by performing consecutive jumps on an inclined surface (15°) while the plane plyometrics (PP) group (n = 10) performed the same jumps on a plane surface. Both groups trained four times per week and performed 8 sets of 10 jumps in each session. Subjects performed squat jumps, counter movement jumps and drop jumps (DJ) prior to and immediately after the training period, while the electromyographic activity of the medial gastrocnemius (MGAS) and tibialis anterior muscles and the architecture of MGAS were recorded. Maximal isokinetic and isometric strength of the plantar flexors were performed. Analysis of variance showed that only the IP group improved fast DJ height performance by 17.4 and 14.4% (20 and 40 cm, p

Ultrasound imaging was used to measure the length of muscle fascicles in human gastrocnemius muscles while the muscle was passively lengthened and shortened by moving the ankle. In some subjects the muscle belly 'buckled' at short lengths. When the gastrocnemius muscle-tendon unit was passively lengthened from its shortest in vivo length by dorsiflexing the ankle, increases in muscle-tendon length were not initially accompanied by increases in muscle fascicle lengths (fascicle length remained constant), indicating muscle fascicles were slack at short muscle-tendon lengths. The muscle-tendon length at which slack is taken up differs among fascicles: some fascicles begin to lengthen at very short muscle-tendon lengths whereas other fascicles remain slack over a large range of muscle-tendon lengths. This suggests muscle fascicles are progressively 'recruited' and contribute sequentially to muscle-tendon stiffness during passive lengthening of the muscle-tendon unit. Even above their slack lengths muscle fascicles contribute only a small part (

Objective: To determine the test-retest reliability of measurements of thickness, fascicle length (L ) and pennation angle (θ) of the vastus lateralis (VL) and gastrocnemius medialis (GM) muscles in older adults. Participants: Twenty-one healthy older adults (11 men and ten women; average age 68·1±5·2years) participated in this study. Methods: Ultrasound images (probe frequency 10MHz) of the VL at two sites (VL site 1 and 2) were obtained with participants seated with knee at 90 flexion. For GM measures, participants lay prone with ankle fixed at 15 dorsiflexion. Measures were taken on two separate occasions, 7days apart (T1 and T2). Results: The ICCs (95% CI) were: VL site 1 thickness=0·96(0·90-0·98); VL site 2 thickness=0·96(0·90-0·98), VL θ=0·87(0·68-0·95), VL L =0·80(0·50-0·92), GM thickness=0·97(0·92-0·99), GM θ=0·85(0·62-0·94) and GM L =0·90(0·75-0·96). The 95% ratio limits of agreement (LOAs) for all measures, calculated by multiplying the standard deviation of the ratio of the results between T1 and T2 by 1·96, ranged from 10·59 to 38·01%. Conclusion: The ability of these tests to determine a real change in VL and GM muscle architecture is good on a group level but problematic on an individual level as the relatively large 95% ratio LOAs in the current study may encompass the changes in architecture observed in other training studies. Therefore, the current findings suggest that B-mode ultrasonography can be used with confidence by researchers when investigating changes in muscle architecture in groups of older adults, but its use is limited in showing changes in individuals over time. © 2011 The Authors. Clinical Physiology and Functional Imaging

Introduction: The relationship of tibialis anterior (TA) muscle architecture, including muscle thickness (MT), cross-sectional area (CSA), pennation angle (PA), and fascicle length (FL), to strength and ankle function was examined in ambulatory individuals with CP and unilateral foot drop. Methods: Twenty individuals with CP participated in muscle ultrasound imaging, unilateral strength testing, and three-dimensional gait analysis. Results: Muscle size (MT and CSA) was positively related to strength, fast gait velocity, and ankle kinematics during walking. Higher PA was related to a more dorsiflexed ankle position at initial contact and inversely with fast gait velocity. FL was related to strength, fast velocity, and step length at a self-selected speed. Conclusions: Muscle architecture partially explains the degree of impairment in strength and ankle function in CP. Treatments to increase TA size and strength may produce some gait improvement, but other factors that may contribute to ankle performance deficits must be considered. Muscle Nerve, 2011

Muscle stretching transiently decreases muscle-blood flow corresponding to a muscle extension. It may disturb a balance between muscular oxygen demand and oxygen supply to muscles and reduce muscle oxygenation. However, muscle-stretching training may improve blood circulatory condition, resulting in the maintained muscle oxygenation during muscle stretching. The aim of this study was to investigate changes in muscle-blood volume (tHb) and tissue oxygenation index (TOI) during muscle stretching determined by using near-infrared spectroscopy (NIRS) in ballet-trained (BT) and untrained (C) subjects. 11 BT women who regularly perform muscle stretching and 11 C women participated in this study. Fascicle lengths, tHb and TOI in the tibialis anterior muscle were measured during passive plantar flexion from ankle joint angles of 120° (baseline) to 140°, 160°, the maximal comfortable position without pain (CP), and the maximal position (MP). At 160°, the % fascicle-length change from baseline was significantly lower in the BT than the C group, however, for the changes in tHb and TOI the significant interaction effect between the 2 groups was not detected. On the other hand, although the increases in the fascicle length from baseline to CP and MP were greater in BT than C, the tHb and TOI reductions were comparable between groups. We concluded that it appears that BT can extend their muscles without excessive reduction in muscle-blood volume and muscle oxygenation at relatively same but absolutely greater muscle-stretching levels than C. The attenuation in these indices during high-level muscle stretching may be associated with the repetitive muscle stretching of long-term ballet training.

[Purpose] The aim of this study was to investigate and compare changes in muscle fascicle and tendon tissue behavior during stretching between a weight-bearing position and non-weight-bearing position. [Subjects] The study subjects were fifteen healthy individuals. [Method] Changes in the calf muscle after stretching in a weight-bearing and a non-weight-bearing position were compared using ultrasonography. Weight-bearing and non-weight-bearing stretching were performed for 30 seconds, and the medial gastrocnemius (MG) muscle fascicle length, pennation angle, and Achilles tendon length were measured before and after stretching. [Results] The post-stretching results in both positions showed increased fascicle length, decreased pennation angle, and increased Achilles tendon length compared with the pre-stretching results. Significant interactions were found between weight-bearing and stretching as evidenced by MG fascicle length and Achilles tendon length; specifically, the non-weight-bearing position increased the length more than the weight-bearing position. [Conclusion] This study revealed that while both weight-bearing and non-weight-bearing stretching were able to stretch the MG muscle and the Achilles tendon, non-weight-bearing stretching was more effective with regard to extending the MG muscle and Achilles tendon.

The purpose of this study was to investigate if force enhancement (FE) in vivo is influenced by stretch-induced changes of muscle architecture. Therefore, 18 subjects performed maximum voluntary isometric (100° knee flexion angle) and isometric-eccentric-isometric stretch contractions (80°–100° ω = 60°s−1) whereby pennation angle and fascicle length of vastus lateralis was determined using ultrasonography. We found significant (2-way repeated ANOVA; α = 0.05) enhanced torque of 5–10% after stretch as well as significant passive FE but no significant differences in muscle architecture between isometric and stretch contractions at final knee angle. Furthermore, EMG recordings during a follow-up study (n= 10) did not show significant differences in activation and mean frequency of contraction conditions. These results indicate that FE in vivo is not influenced by muscle architectural changes due to stretch.

Wearing high heels (HH) places the calf muscle–tendon unit (MTU) in a shortened position. As muscles and tendons are highly malleable tissues, chronic use of HH might induce structural and functional changes in the calf MTU. To test this hypothesis, 11 women regularly wearing HH and a control group of 9 women were recruited. Gastrocnemius medialis (GM) fascicle length, pennation angle and physiological cross-sectional area (PCSA), the Achilles' tendon (AT) length, cross-sectional area (CSA) and mechanical properties, and the plantarflexion torque–angle and torque–velocity relationships were assessed in both groups. Shorter GM fascicle lengths were observed in the HH group (49.6±5.7 mm vs 56.0±7.7 mm), resulting in greater tendon-to-fascicle length ratios. Also, because of greater AT CSA, AT stiffness was higher in the HH group (136.2±26.5 N mm–1 vs 111.3±20.2 N mm–1). However, no differences in the GM PCSA to AT CSA ratio, torque–angle and torque–velocity relationships were found. We conclude that long-term use of high-heeled shoes induces shortening of the GM muscle fascicles and increases AT stiffness, reducing the ankle's active range of motion. Functionally, these two phenomena seem to counteract each other since no significant differences in static or dynamic torques were observed. * AT : Achilles' tendon CSA : cross-sectional area CTRL : control E : Young's modulus GL : gastrocnemius lateralis muscle GM : gastrocnemius medialis muscle HH : high heels K : tendon stiffness L f : fascicle length L tend : tendon length MA : moment arm MRI : magnetic resonance imaging MTU : muscle–tendon unit MVC : maximum voluntary contraction PCSA : physiological cross-sectional area SOL : soleus muscle TA : tibialis anterior muscle v max : maximum contraction velocity v opt : optimal contraction velocity θ : pennation angle

In humans, an inhibitory via Ia afferent pathway from the medial gastrocnemius (MG) to the soleus (SOL) motoneuron pool has been suggested. Herein, we examined the relation between MG fascicle length changes and the SOL H-reflex modulation during passive knee movement. Twelve subjects performed static and passive (5 degrees s(-1)) knee movement tasks with the ankle immobilized using an isokinetic dynamometer in sitting posture. The maximal H- and M-waves were measured at four target angles (20 degrees, 40 degrees, 60 degrees, and 80 degrees flexion from full knee extension). The MG fascicles length and velocity were measured using a B-mode ultrasonic apparatus. Results demonstrated that the SOL Hmax/Mmax; i.e., ratio of the maximal H- to M-waves, was attenuated with increasing MG fascicle length in static tasks. The SOL Hmax/Mmax at 20 degrees was significantly attenuated compared with 60 degrees and 80 degrees with increasing MG fascicle length and lengthening velocity in passive knee extension. However, no significant differences in the SOL Hmax/Mmax were found across the target angles in the passive knee flexion task. In conclusion, as muscle spindles increase their discharge with lengthening fascicle velocity, but keep silent when fascicles shorten, our data suggest that lengthening the MG facilitates an inhibitory Ia pathway from MG to SOL, and modulates SOL motoneuron activity during movements.

AIMS We assessed focal adhesion kinase (FAK) response to concentric (CON) versus eccentric (ECC) resistance training (RT) at two vastus lateralis (VL) sites, and the relationships between FAK, muscle protein synthesis (MPS), and morphological remodeling. METHODS Six young males trained both legs unilaterally 3 times/week for 8 weeks; one leg performed CON RT, the contralateral performed ECC RT. Muscle biopsies were collected after training from VL midbelly (MID) and distal (Distal) sites at 0, 4, 8 weeks. FAK content and activation were evaluated by immunoblotting. MPS was assessed by deuterium-oxide tracer; morphological adaptations were evaluated by ultrasound and DXA. RESULTS pY397-FAK 8 weeks levels were ~4-fold greater after ECC at the Distal site compared to CON (p

The aim of this study was to examine the differences in muscle architecture during isometric tests between children and adults. Eight boys (age= 11.2 ± 0.26 years) and eight men (age= 22.3 ± 2.01 years) performed plantar flexion isometric efforts at angles of -15°, 0°, 15° at 0%, 40%, 60%, 80% of MVC. Analysis of variance tests indicated that adults showed greater fascicle length from rest to 80% of MVC (p < .05), greater pennation angle at 80% and 100% of MVC (p < .05) and greater aponeuroses displacement at levels of effort greater than 60% of MVC (p < .05). These differences observed in MG would appear to favor better utilization of the force-length and the force-velocity relationships, of the muscle in adults compared with children.

To investigate the relationship between fascicle behavior and joint torque, the fascicle behavior of the triceps surae during isometric and eccentric (30 and 60 deg/s) plantar flexion by maximal voluntary and submaximal electrical activation (MVA and SEA) was measured by real-time ultrasonography. Eccentric torque at 30 and 60 deg/s was significantly higher than isometric torque under SEA, but not under MVA. However, fascicle length did not significantly differ between isometric and eccentric trials under either condition. Therefore, the difference in developed torque by MVA and SEA cannot be explained by fascicle behavior. Under both MVA and SEA conditions, eccentric torque at 30 and 60 deg/s was equivalent. Similarly, fascicle lengthening velocities at 30 and 60deg/s did not show any significant difference. Such fascicle behavior can be attributed to the influence of tendinous tissue and pennation angle, and lead to a lack of increase in eccentric torque with increasing angular velocity.

Changes in contractile rate of force development (RFD), measured within a short time interval from contraction initiation, were measured after a period of strength training that led to increases in muscle fascicle length but no measurable change in neuromuscular activity. The relationship between training-induced shifts in the moment-angle relation and changes in RFD measured to 30 ms (i.e., early) and 200 ms (i.e., late) from the onset of isometric knee extension force were examined; shifts in the moment-angle relation were used as an overall measure of changes in quadriceps muscle fascicle length. A significant proportion of the variance in RFD measured only in the initial contraction phase (0-30 ms) could be explained by shifts in the moment-angle relation (r=-0.66-0.71; R2=0.44-0.50). Training-induced increases in muscle fascicle length may lead to a reduced or complete lack of adaptive gains in contractile RFD, especially in the early contraction phase.

Experimental descriptive laboratory study.To describe the change in fascicle length of the human vastus lateralis (VL) muscle during the stance phase of stair ascent and descent.Muscle fascicle length changes during lower limb functional activities, such as walking and jumping, do not always coincide with joint angle changes.Thirty-three healthy, college-age women walked up and down 4 standard steps. VL fascicle length and pennation angle were measured using real-time ultrasonography. Knee angle was monitored using an electrical goniometer. Foot switches indicated foot contact and release. VL muscle activity was monitored using surface electrodes. The VL muscle-tendon complex and tendon length were calculated based on published models.During initial weight acceptance in stair ascent, the knee joint extended only 3 degrees , VL muscle activity increased to a maximum, VL fascicles shortened, and the tendon lengthened. As the knee extended to ascend the step, the fascicles and tendon shortened throughout the movement. During weight acceptance in stair descent, VL muscle activity increased, VL fascicle length did not change significantly, but the tendon lengthened as 10 degrees of knee flexion occurred. As the knee flexed to complete descent, VL muscle activity peaked, and VL fascicles and tendon lengthened.VL fascicles shorten and lengthen as expected during the respective knee extension and knee flexion phases of stair ascent and descent. However, during initial weight acceptance in both stair ascent and descent, the fascicle length change did not coincide with the knee joint kinematics.

The aim of this study was to assess whether the in vivo specific force and architectural characteristics of the lateral gastrocnemius (GL) muscle of early pubescent boys ( n = 11, age = 10.9 ± 0.3 yr, Tanner stage 2) differed from those of adult men ( n = 12, age = 25.3 ± 4.4 yr). Plantarflexor torque was 55% lower in the boys (77.4 ± 21.4 N·m) compared with the adults (175.6 ± 31.7 N·m, P < 0.01). Physiological cross-sectional area (PCSA), determined in vivo using ultrasonography and MRI, was 52% smaller in the boys ( P < 0.01). No difference was found in pennation angle, or in the ratio of fascicle length ( Lf) to muscle length between the boys and men. Moment arm length was 25% smaller in the boys ( P < 0.01). Antagonist coactivation, assessed using surface EMG on the dorsiflexors, was not different between the boys and men (11.8 ± 6.7% and 13.5 ± 5.8%, respectively). Surprisingly, GL force normalized to PCSA (specific force) was significantly higher (21%) in the boys than in the men (13.1 ± 2.0 vs. 15.9 ± 2.7 N/cm2, P < 0.05). This finding could not be explained by differences in moment arm length, muscle activation, or architecture, and other factors, such as tendinous characteristics and/or changes in moment arm length with contraction, may be held responsible. These observations warrant further investigation.

Muscles and tendons are highly adaptive to changes in chronic loading, though little is known about the adaptative time course. We tested the hypothesis that, in response to unilateral lower limb suspension (ULLS), the magnitude of tendon mechanical adaptations would match or exceed those of skeletal muscle. Seventeen men (1.79 +/- 0.05 m, 76.6 +/- 10.3 kg, 22.3 +/- 3.8 years) underwent ULLS for 23 days (n = 9) or acted as controls (n = 8). Knee extensor (KE) torque, voluntary activation (VA), cross-sectional area (CSA) (by magnetic resonance imaging), vastus lateralis fascicle length (L(f)) and pennation angle (), patellar tendon stiffness and Young's modulus (by ultrasonography) were measured before, during and at the end of ULLS. After 14 and 23 days (i) KE torque decreased by 14.8 +/- 5.5% (P < 0.001) and 21.0 +/- 7.1% (P < 0.001), respectively; (ii) VA did not change; (iii) KE CSA decreased by 5.2 +/- 0.7% (P < 0.001) and 10.0 +/- 2.0% (P < 0.001), respectively; L(f) decreased by 5.9% (n.s.) and 7.7% (P < 0.05), respectively, and by 3.2% (P < 0.05) and 7.6% (P < 0.01); (iv) tendon stiffness decreased by 9.8 +/- 8.2% (P < 0.05) and 29.3 +/- 11.5% (P < 0.005), respectively, and Young's modulus by 9.2 +/- 8.2% (P < 0.05) and 30.1 +/- 11.9% (P < 0.01), respectively, with no changes in the controls. Hence, ULLS induces rapid losses of KE muscle size, architecture and function, but not in neural drive. Significant deterioration in tendon mechanical properties also occurs within 2 weeks, exacerbating in the third week of ULLS. Rehabilitation to limit muscle and tendon deterioration should probably start within 2 weeks of unloading.