Effect of resistance training to muscle failure vs non-failure on strength,hypertrophy and muscle architecture in trained individuals

The aim of this study was to compare the effects of resistance training to muscle failure (RT-F) and non-failure (RT-NF) on muscle mass, strength and activation of trained individuals. We also compared the effects of these protocols on muscle architecture parameters. A within-subjects design was used in which 14 participants had one leg randomly assigned to RT-F and the other to RT-NF. Each leg was trained 2 days per week for 10 weeks. Vastus lateralis (VL) muscle cross-sectional area (CSA), pennation angle (PA), fascicle length (FL) and 1-repetition maximum (1-RM) were assessed at baseline (Pre) and after 20 sessions (Post). The electromyographic signal (EMG) was assessed after the training period. RT-F and RT-NF protocols showed significant and similar increases in CSA (RT-F: 13.5% and RT-NF: 18.1%; P < 0.0001), PA (RT-F: 13.7% and RT-NF: 14.4%; P < 0.0001) and FL (RT-F: 11.8% and RT-NF: 8.6%; P < 0.0001). All protocols showed significant and similar increases in leg press (RT-F: 22.3% and RT-NF: 26.7%; P < 0.0001) and leg extension (RT-F: 33.3%, P < 0.0001 and RT-NF: 33.7%; P < 0.0001) 1-RM loads. No significant differences in EMG amplitude were detected between protocols (P > 0.05). In conclusion, RT-F and RT-NF are similarly effective in promoting increases in muscle mass, PA, FL, strength and activation.     

In vivo fascicle length measurements via B-mode ultrasound imaging with single vs dual transducer arrangements

Ultrasonography is a useful technique to study muscle contractions in vivo, however larger muscles like vastus lateralis may be difficult to visualise with smaller, commonly used transducers. Fascicle length is often estimated using linear trigonometry to extrapolate fascicle length to regions where the fascicle is not visible. However, this approach has not been compared to measurements made with a larger field of view for dynamic muscle contractions. Here we compared two different single-transducer extrapolation methods to measure VL muscle fascicle length to a direct measurement made using two synchronised, in-series transducers. The first method used pennation angle and muscle thickness to extrapolate fascicle length outside the image (extrapolate method). The second method determined fascicle length based on the extrapolated intercept between a fascicle and the aponeurosis (intercept method). Nine participants performed maximal effort, isometric, knee extension contractions on a dynamometer at 10° increments from 50 to 100° of knee flexion. Fascicle length and torque were simultaneously recorded for offline analysis. The dual transducer method showed similar patterns of fascicle length change (overall mean coefficient of multiple correlation was 0.76 and 0.71 compared to extrapolate and intercept methods respectively), but reached different absolute lengths during the contractions. This had the effect of producing force–length curves of the same shape, but each curve was shifted in terms of absolute length. We concluded that dual transducers are beneficial for studies that examine absolute fascicle lengths, whereas either of the single transducer methods may produce similar results for normalised length changes, and repeated measures experimental designs.     

Measurement of active muscle stiffness with and without the stretch reflex

The purpose of the present study was to evaluate active muscle stiffness with the stretch reflex according to changes (in 110-ms period after stretching) in torque and fascicle length during slower angular velocity (peak angular velocity of 100 deg·s⁻¹) in comparison with active muscle stiffness without the stretch reflex (in 60-ms period after stretching) during slower and faster (peak angular velocity of 250 deg·s⁻¹) angular velocities. Active muscle stiffness in the medial gastrocnemius muscle was calculated according to changes in estimated muscle force and fascicle length with slower and faster stretching during submaximal isometric contractions (10–90% maximal voluntary contractions). Active muscle stiffness significantly increased for both angular velocities and analyzed periods as torque levels exerted became higher. The effects of angular velocities and the interaction between angular velocities and torque levels were not significantly different between 250 deg·s⁻¹ (in 60-ms period after stretching) and 100 deg·s⁻¹ (in 110-ms period after stretching) conditions. The effects of the analyzed periods and the interaction between analyzed periods and torque levels were not significantly different between the analyzed periods (60-ms and 110-ms periods after stretching) for the 100 deg·s⁻¹ condition. Furthermore, active muscle stiffness measured during the same angular velocity had significant correlations between those calculated in the different analyzed periods, whereas those under 250 deg·s⁻¹ (60-ms period after stretching) did not correlate with those under 100 deg·s⁻¹ (110-ms period after stretching). These results suggest that active muscle stiffness is not influenced by the stretch reflex.     

Reproducibility of gastrocnemius medialis muscle architecture during treadmill running

The purpose of this study was to assess the reproducibility of fascicle length (FL) and pennation angle (PA) of gastrocnemius medialis (GM) muscle during running in vivo. Twelve male recreational long distance runners (mean ± SD; age: 24 ± 3 years, mass: 76 ± 7 kg) ran on a treadmill at a speed of 3.0 m/s, wearing their own running shoes, for two different 10 min sessions that were at least 2 days apart. For each test day 10 acceptable trials were recorded. Ankle and knee joint angle data were recorded by a Vicon 624 system with three cameras operating at 120 Hz. B-mode ultrasonography was used to examine fascicle length and pennation angle of gastrocnemius medialis muscle. The ultrasound probe was firmly secured on the muscle belly using a lightweight foam fixation. The results indicated that fascicle length and pennation angle demonstrated high reproducibility values during treadmill running both for within and between test days. The root mean square scores between the repeated waveforms of pennation angle and fascicle length were small (∼2° and ∼3.5 mm, respectively). However, ∼14 trials for pennation angle and ∼9 trials for fascicle length may be required in order to record accurate data from muscle architecture parameters. In conclusion, ultrasound measurements may be highly reproducible during dynamic movements such as treadmill running, provided that a proper fixation is used in order to assure the constant location and orientation of the ultrasound probe throughout the movement.     

Heterogeneous fascicle behavior within the biceps femoris long head at different muscle activation levels

Magnetic resonance and ultrasound imaging have shown hamstring strain injuries occur most often in the biceps femoris long head (BFLH), and particularly in the proximal vs. distal region of this muscle. Animal research and musculoskeletal modeling (MSK) have detected heterogeneous fascicle behavior within muscle regions, and within fascicles. Understanding architectural behavior differences during muscle contractions may help to discern possible mechanisms behind proximal BFLH injuries. The purpose of our study was to assess the magnitude of shortening of the proximal and distal fascicles of the BFLH under a range of muscle activation levels under isometric conditions using ultrasound imaging (US). Thirteen healthy adults performed targeted sustained isometric contractions while US were taken of the entire BFLH. Measurements of fascicle lengths in both muscle regions were compared at 20%, 30%, 50%, and 67% MVIC. The results showed that while both regions shortened significantly with activation, the proximal fascicles were significantly longer, regardless of activation level (~38%), and shortened significantly more than the distal fascicles overall (~40%), and cumulatively at higher activation levels (30% and above). No significant strain differences were found between the two regions. These data suggest heterogeneous fascicle behavior exists in an absolute sense; however, differences in behavior are eliminated when normalized (strain). Coupled with MSK literature, the absence of regional fascicle strain differences in this study may indicate strain heterogeneity is not detectable at the whole fascicle level. Further knowledge of this commonly strained muscle?s regional behavior during dynamic movements could provide evidence of proximal hamstring strain predisposition.     

Validity of fascicle length estimation in the vastus lateralis and vastus intermedius using ultrasonography

The purpose of this study was to determine the validity of fascicle length estimation in the vastus lateralis (VL) and vastus intermedius (VI) using ultrasonography. The fascicle lengths of the VL and VI muscles were measured directly (dFL) using calipers, and were estimated (estmFL) using ultrasonography, in 10 legs from five Thiel’s embalmed cadavers. To determine the validity of the estmFLs, FL was estimated using five previously published models and compared with dFL. The intraclass correlation coefficients (ICCs) of two of the five models were > 0.75, indicating that these estimates were valid. Both of these models combined measurement of the length of the visible part of the fascicle with linear extrapolation of the length of the part of the fascicle that was not visible on the sonographic image. The ICCs and absolute% difference were best in models that used appropriate pennation angles. These results suggest that two of the five previously published models are valid for obtaining estmFL of the VL and VI using ultrasonography.     

Magnetic resonance and diffusion tensor imaging analyses indicate heterogeneous strains along human medial gastrocnemius fascicles caused by submaximal plantar-flexion activity

Sarcomere length changes are central to force production and excursion of skeletal muscle. Previous modeling indicates non-uniformity of that if mechanical interaction of muscle with its surrounding muscular and connective tissues is taken into account. Hence, quantifying length changes along the fascicles of activated human muscle in vivo is crucial, but this is lacking due to technical complexities. Combining magnetic resonance imaging deformation analyses and diffusion tensor imaging tractography, the aim was to test the hypothesis that submaximal plantar flexion activity at 15% MVC causes heterogeneous length changes along the fascicles of human medial gastrocnemius (GM) muscle. A general fascicle strain distribution pattern shown for all subjects indicates that proximal track segments are shortened, whereas distal ones are lengthened (e.g., by 13% and 29%, respectively). Mean fiber direction strains of different tracts also shows heterogeneity (for up to 57.5% of the fascicles). Inter-subject variability of amplitude and distribution of fascicle strains is notable. These findings confirm the hypothesis and are solid indicators for the functionally dependent mechanics of human muscle, in vivo. Heterogeneity of fascicle strains can be explained by epimuscular myofascial force transmission. To the best of our knowledge, this is the first study, which quantified local deformations along human skeletal muscle fascicles caused by sustained submaximal activation. The present approach and indicated fascicle strain heterogeneity has numerous implications for muscle function in health and disease to estimate the muscle’s contribution to the joint moment and excursion and to evaluate mechanisms of muscle injury and several treatment techniques.     

Ultrasonographic quantification of architectural response in tibialis anterior to neuromuscular electrical stimulation

While muscle contraction in voluntary efforts has been widely investigated, little is known about contraction during neuromuscular electrical stimulation (NMES). The aim of this study was to quantify in vivo muscle architecture of agonist and antagonist muscles at the ankle joint during NMES. Muscle fascicle lengths and pennation angles of the tibialis anterior (TA) and lateral gastrocnemius muscles were assessed via ultrasonography in 8 healthy young males. Measures were obtained during maximal NMES and torque-matched voluntary dorsiflexion contractions. In the TA, NMES induced a shorter fascicle length (67.2 ± 8.1 mm vs 74.6 ± 11.4 mm; p = 0.04) and a greater pennation angle (11.0 ± 2.4° vs 9.3 ± 2.5°; p = 0.03) compared with voluntary torque-matched dorsiflexion contractions. Architectural responses in the antagonist lateral gastrocnemius muscle did not significantly differ from rest or between voluntary and electrically induced contractions (p > 0.05). Contraction of the antagonist muscle was not a contributing factor to a greater fascicle shortening and increased pennation angle in the TA during NMES. TA architectural response during NMES likely arose from the contribution of muscle synergists during voluntary contractions coupled with a potentially localized contractile activity under the stimulation electrodes during NMES induced contractions.     

Theoretical considerations for muscle-energy savings during distance running

We have recently demonstrated that the triceps surae muscles energy cost (EC_TS) represents a substantial portion of the total metabolic cost of running (E_run). Therefore, it seems relevant to evaluate the factors which dictate EC_TS, namely the amount and velocity of shortening, since it is likely these factors will dictate E_run. E_run and triceps surae morphological and AT mechanical properties were obtained in 46 trained and elite male and female distance runners using ultrasonography and dynamometry. EC_TS (J·stride⁻¹) at the speed of lactate threshold (sLT) was estimated from AT force and crossbridge mechanics and energetics. To estimate the relative impact of these factors on EC_TS, mean values for running speed, body mass, resting fascicle length (L_f), Achilles tendon stiffness and moment arm and maximum isometric plantarflexion torque were obtained. EC_TS was calculated across a range (mean ± 1 sd) of values for each independent factor. Average sLT was 233 m·min⁻¹. At this speed, EC_TS was 255 J·stride⁻¹. Estimated fascicle shortening velocity was 0.08 V_max and the level of muscle activation was 84.7% of maximum isometric torque. Compared to the EC_TS calculated from the lowest range of values obtained for each independent factor, higher AT stiffness was associated with a 39% reduction in EC_TS, 81% reduction in fascicle shortening velocity and a 31% reduction in muscle activation. Longer AT moment arms and elevated body masses were associated with an increase in EC_TS of 18% and 23%, respectively. These results demonstrate that a low EC_TS is achieved primarily from a high AT stiffness and low body mass, which is exemplified in elite distance runners.     

Demonstration of extended field-of-view ultrasound’s potential to increase the pool of muscles for which in vivo fascicle length is measurable

Static, B-mode ultrasound is the most common method of measuring fascicle length in vivo. However, most forearm muscles have fascicles that are longer than the field-of-view of traditional ultrasound (T-US). As such, little work has been done to quantify in vivo forearm muscle architecture. The extended field-of-view ultrasound (EFOV-US) method, which fits together a sequence of B-mode images taken from a continuous ultrasound scan, facilitates direct measurements of longer, curved fascicles. Here, we test the validity and reliability of the EFOV-US method for obtaining fascicle lengths in the extensor carpi ulnaris (ECU). Fascicle lengths from images of the ECU captured in vivo with EFOV-US were compared to lengths from a well-established method, T-US. Images were collected in a joint posture that shortens the ECU such that entire fascicle lengths were captured within a single T-US image. Resulting measurements were not significantly different (p = 0.18); a Bland-Altman test demonstrated their agreement. A novice sonographer implemented EFOV-US in a phantom and in vivo on the ECU. The novice sonographer’s measurements from the ultrasound phantom indicate that the combined imaging and analysis method is valid (average error = 2.2 ± 1.3 mm) and the in vivo fascicle length measurements demonstrate excellent reliability (ICC = 0.97). To our knowledge, this is the first study to quantify in vivo fascicle lengths of the ECU using any method. The ability to define a muscle’s architecture in vivo using EFOV-US could lead to improvements in diagnosis, model development, surgery guidance, and rehabilitation techniques.