Electromyographic,but not mechanomyographic amplitude–force relationships,distinguished differences in voluntary activation capabilities between individuals

The purpose of the present study was to examine the influence of activation capabilities on the electromyography (EMG_RMS) and mechanomyography amplitude (MMG_RMS)–force relationships of the vastus lateralis (VL) and rectus femoris (RF). Thirteen men (mean ± SD; age = 22 ± 3 year) performed nine submaximal contractions (10–90% maximal voluntary contraction [MVC]) with the interpolated twitch technique performed during a separate contraction at 90% MVC to calculate percent voluntary activation (%VA). Nine participants with >90% VA were categorized into the high-activated group with the remaining categorized into the moderate-activated group. Slopes (b terms) were calculated from the log-transformed EMG_RMS and MMG_RMS–force relationships. The b terms (collapsed across the VL and RF) for the EMG_RMS–force relationships were greater for the high- (1.29 ± 0.31) than the moderate-activated (1.10 ± 0.20) group. In contrast, there were no differences in the b terms for the MMG_RMS–force relationships between the high- and moderate-activated groups. For the EMG_RMS and MMG_RMS–force relationships, the b terms were greater for the RF (1.38 ± 0.30, 0.81 ± 0.20) than the VL (1.08 ± 0.19, 0.60 ± 0.13) collapsed across groups. The b terms from the EMG_RMS–force relationships, but not the MMG_RMS–force relationships, reflected differences in %VA.     

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.     

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.     

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.     

EMG normalization to study muscle activation in cycling

The value of electromyography (EMG) is sensitive to many physiological and non-physiological factors. The purpose of the present study was to determine if the torque–velocity test (T–V) can be used to normalize EMG signals into a framework of biological significance. Peak EMG amplitude of gluteus maximus (GMAX), vastus lateralis (VL), rectus femoris (RF), biceps femoris long head (BF), gastrocnemius medialis (GAS) and soleus (SOL) was calculated for nine subjects during isometric maximal voluntary contractions (IMVC) and torque–velocity bicycling tests (T–V). Then, the reference EMG signals obtained from IMVC and T–V bicycling tests were used to normalize the amplitude of the EMG signals collected for 15 different submaximal pedaling conditions. The results of this study showed that the repeatability of the measurements between IMVC (from 10% to 23%) and T–V (from 8% to 20%) was comparable. The amplitude of the peak EMG of VL was 99 ± 43% higher (p < 0.001) when measured during T–V. Moreover, the inter-individual variability of the EMG patterns calculated for submaximal cycling exercises differed significantly when using T–V bicycling normalization method (GMAX: 0.33 ± 0.16 vs. 1.09 ± 0.04, VL: 0.07 ± 0.02 vs. 0.64 ± 0.14, SOL: 0.07 ± 0.03 vs. 1.00 ± 0.07, RF: 1.21 ± 0.20 vs. 0.92 ± 0.13, BF: 1.47 ± 0.47 vs. 0.84 ± 0.11). It was concluded that T–V bicycling test offers the advantage to be less time and energy-consuming and to be as repeatable as IMVC tests to measure peak EMG amplitude. Furthermore, this normalization method avoids the impact of non-physiological factors on the amplitude of the EMG signals so that it allows quantifying better the activation level of lower limb muscles and the variability of the EMG patterns during submaximal bicycling exercises.     

Non-invasive assessment of muscle fiber conduction velocity during an incremental maximal cycling test

Muscle fiber conduction velocity (MFCV) gives critical information on neuromuscular control and can be considered a size principle parameter, being suggestive of motor unit recruitment strategies. MFCV has been recently measured during constant-load sub-maximal cycling exercise and was found to correlate positively with percentage of type I myosin heavy chain.The aim of this study was to test the hypothesis that MFCV measured during an incremental cycling test using surface electromyography (sEMG), can be sensitive to the different metabolic requests elicited by the exercise. In particular, the relationship between ventilatory threshold (T-vent), V^′O_2max and MFCV was explored.Eleven male physically active subjects (age 30 ± 9 years) undertook a 1-min incremental cycling test to exhaustion. T-vent and V^′O_2max were measured using an open circuit breath by breath gas analyzer. The sEMG was recorded from the vastus lateralis muscle with an adhesive 4-electrodes array, and the MFCV was computed on each sEMG burst over the last 30-s of each step.The mean V^′O_2max obtained during the maximal test was 53.32 ± 2.33 ml kg^?1 min^?1, and the T-vent was reached at 80.77 ± 3.49% of V^′O_2max. In all subjects reliable measures of MFCV were obtained at every exercise intensity (cross correlation values >0.8). MFCV increased linearly with the mechanical load, reaching a maximum value of 4.28 ± 0.67 m s^?1 at an intensity corresponding to the T-vent. Thereafter, MFCV declined until maximal work intensities. This study demonstrates that MFCV can be used as non-invasive tool to infer MUs recruitment/derecruitment strategies even during dynamic exercise from low to maximal intensities.     

The effects of cycling cadence on the phases of joint power,crank power,force and force effectiveness

We examined the influence of cadence in cycling technique by quantifying phase relationships for a number of important variables at the crank and lower extremity joints. Any difference in the effect of cadence on force, effectiveness, and power phases would indicate an essential change in coordination pattern. Cycle kinetics was recorded for 10 male competitive cyclists at five cadences (60–100 rpm) at submaximal load (260 W). Joint powers were calculated using inverse dynamics methods. All data were expressed as a function of crank position. The phase of the crank mechanical profiles (total force, crank and joint power, and effectiveness) was calculated using four methods: crank angle of maximum (MA) and minimum (MI), fitting a sine wave (SI) and by cross-correlation (XC). These methods, apart from the MA method, showed the same relative phase. The variables, however, showed different phases being expressed as time lag: force effectiveness: 0.131 (±0.034) s; total force: 0.149 (±0.021) s; power: 0.098 (±0.027) s. The phases in joint powers hip 0.071 (±0.008), knee 0.082 (±0.009), and hip 0.077 (±0.012) were only well described by XC, and were somewhat lower than the crank power phase. These differences indicate the potential effect of inertia of the lower limb in phase shifts from joints to crank. Furthermore, the differences between the various crank variables indicate a change of technique with cadence.     

In vivo moment generation and architecture of the human plantar flexors after different shortening–stretch cycles velocities

The purpose of this study was to examine the moment generation of the human plantar flexors and the architecture of the gastrocnemius medialis muscle during and after shortening–stretch cycles in vivo. Fourteen male subjects (30 ± 7 years, 177 ± 7 cm, 80 ± 9 kg) performed a series of electro-stimulated shortening–stretch plantar flexion contractions. The shortening–stretch cycles were performed at three constant angular velocities (25°/s, 50°/s, 100°/s), two amplitudes (15° and 25° ankle angle changes) and at two different stimulation frequencies (30 Hz and 85 Hz). The resultant ankle joint moments were calculated through inverse dynamics. Pennation angle and fascicle length of the m. gastrocnemius medialis at rest and during contractions were measured using ultrasonography. The corresponding ankle moments, kinematics and changes in muscle architecture were analysed at seven time intervals. A three-way analysis of variance (amplitude × velocity × stimulation frequency) and post-hoc test with Bonferroni correction were used to check the amplitude, velocity and stimulation level related effects on moment enhancement (α = 0.05). The results show an ankle joint moment enhancement after shortening–stretch cycles influenced by muscle architectural changes. We found 2–3% isometric ankle joint moment enhancement at steady state, 1.5–2.0 s after the shortening–stretch cycle. However, the observed alteration in muscle architecture after the imposed perturbation, could lead to an underestimation (1–3%) of joint moment enhancement due to the force–length relationship of the triceps surae. Furthermore, the enhancement observed was independent of the shortening–stretch amplitude, velocity and stimulation frequency.     

The impact of altered task mechanics on timing and duration of eccentric bi-articular muscle contractions during cycling

In order to understand muscle adaptations to altered task mechanics during cycling, this study investigated the impact of altered seat height and cadence on timing and duration of gastrocnemius (GAST), biceps femoris (BF) and vastus lateralis (VL) eccentric contractions and muscle activation patterns, and cycling economy. Ten male cyclists completed 9 × 5 min of cycling at 3 seat heights and 3 cadences. Three-dimensional leg kinematics and muscle activation patterns were recorded to estimate timing of eccentric muscle contractions. Onset, offset and duration of eccentric contractions and, onset, offset and duration of muscle activation were calculated, along with cycling economy. Duration of GAST and VL eccentric contractions decreased with increasing seat height due to earlier offset of eccentric muscle contractions. Duration of BF eccentric contractions significantly increased with seat height due to a later eccentric contraction offset. Offset of GAST and BF muscle activation occurred earlier with increasing cadence. Cycling economy was significantly affected by cadence but not seat height. The results suggest that as a consequence of altered seat height, proprioceptive feedback is used to fine-tune the timing of bi-articular eccentric muscle contractions. These results may have implications for seat height self-selection.     

Estimating in vivo passive forces of the index finger muscles: Exploring model parameters

We compared predicted passive finger joint torques from a biomechanical model that includes the exponential passive muscle force–length relationship documented in the literature with finger joint torques estimated from measures in ten adult volunteers. The estimated finger joint torques were calculated from measured right index fingertip force, joint postures, and anthropometry across 18 finger and wrist postures with the forearm muscles relaxed. The biomechanical model predicting passive finger joint torques included three extrinsic and three intrinsic finger muscles. The values for the predicted passive joint torques were much larger than the values calculated from the fingertip force and posture measures with an average RMS error of 7.6 N cm. Sensitivity analysis indicated that the predicted joint torques were most sensitive to passive force–length model parameters compared to anthropometric and postural parameters. Using Monte Carlo simulation, we determined a new set of values for the passive force–length model parameters that reduced the differences between the joint torques calculated from the two methods to an average RMS value of 0.5 N cm, a 94% average improvement of error from the torques predicted using the existing data. These new parameter values did vary across individuals; however, using an average set for the parameter values across subjects still reduced the average RMS difference to 0.8 N cm. These new parameters may improve dynamic modeling of the finger during sub-maximal force activities and are based on in vivo data rather than traditional in vitro data.     

The effects of muscle architectural change with a pre-motion silent period on the subsequent muscular output during rapid voluntary movement

This study aimed to determine the characteristics of the in vivo behaviour of human muscle architecture during a pre-motion silent period (PMSP) using ultrasonography. Subjects were requested to perform rapid knee extension with vertical jumping. Electromyographic signals were recorded from the vastus lateralis (VL), vastus medialis, and biceps femoris muscles. Ultrasonic images were recorded from the VL. We found that the cross point between the fascicle and deep aponeurosis in the VL moved to the distal side before the rapid vertical jumps with PMSP. This cross point movement with PMSP was of low amplitude (mean: 1.0 ± 0.3 mm) and velocity (22.2 ± 6.1 mm/s). The amplitude and velocity of the cross point movement were significantly positively related to the angular peak velocity of knee extensor during rapid vertical jumping in trials with PMSP. These results suggest that although low levels of pre-movement muscle architectural change with PMSP may be the result of muscle relaxation behaviour rather than the result of muscle stretching behaviour, this pre-movement effect can influence subsequent muscular performance during a rapid voluntary movement. PMSP may allow pre-movement muscle architectural change to generate a better muscular condition to increase neural activation during the subsequent rapid voluntary contraction.     

Endurance and strength training effects on physiological and muscular parameters during prolonged cycling

PurposeThis study investigated the effects of a combined endurance and strength training on the physiological and neuromuscular parameters during a 2-h cycling test.MethodsFourteen triathletes were assigned to an endurance-strength training group and an endurance-only training group. They performed three experimental trials before and after training: an incremental cycling test to exhaustion, a maximal concentric lower-limbs strength measurement and a 2-h cycling exercise. Physiological parameters, free cycling chosen cadence and the EMG of Vastus Lateralis (VL) and Rectus Femoris (RF) were analysed during the 2-h cycling task before and after a strength training programme of 5 weeks (three times per week).ResultsThe results showed that the maximum strength and the isometric maximal voluntary contraction (isoMVC) after training were significantly higher (P < 0.01) and lower (P < 0.01) than those before training, respectively, in endurance-strength training group and endurance-only group. The physiological variables measured during the cycling tests and the progressive increase (P < 0.01) in EMGi_(VL) and EMGi_(RF) throughout the 2-h cycling test did not differ between the two groups before and after training, except for the variation of EMGi_(VL) over the cycle time which was stabilized during the second hour of the 2-h cycling test due to training in endurance-strength training group. The decrease in free cycling chosen cadence observed in pre-training (P < 0.01) was also replaced by a steady free cycling chosen cadence for the endurance-strength training group during the second hour of exercise.ConclusionThis study confirmed the decrease in the free cycling chosen cadence with exercise duration and demonstrated that a specific combined endurance and strength training can prevent this decrease during a 2-h constant cycling exercise.     

Intra-session repeatability of lower limb muscles activation pattern during pedaling

Assessment of intra-session repeatability of muscle activation pattern is of considerable relevance for research settings, especially when used to determine changes over time. However, the repeatability of lower limb muscles activation pattern during pedaling is not fully established. Thus, we tested the intra-session repeatability of the activation pattern of 10 lower limb muscles during a sub-maximal cycling exercise.Eleven triathletes participated to this study. The experimental session consisted in a reference sub-maximal cycling exercise (i.e. 150 W) performed before and after a 53-min simulated training session (mean power output = 200 ± 12 W). Repeatability of EMG patterns was assessed in terms of muscle activity level (i.e. RMS of the mean pedaling cycle and burst) and muscle activation timing (i.e. onset and offset of the EMG burst) for the 10 following lower limb muscles: gluteus maximus (GMax), semimembranosus (SM), Biceps femoris (BF), vastus medialis (VM), rectus femoris (RF), vastus lateralis (VL), gastrocnemius medianus (GM) and lateralis (GL), soleus (SOL) and tibialis anterior (TA).No significant differences concerning the muscle activation level were found between test and retest for all the muscles investigated. Only VM, SOL and TA showed significant differences in muscle activation timing parameters. Whereas ICC and SEM values confirmed this weak repeatability, cross-correlation coefficients suggest a good repeatability of the activation timing parameters for all the studied muscles.Overall, the main finding of this work is the good repeatability of the EMG pattern during pedaling both in term of muscle activity level and muscle activation timing.     

Diminished sub-maximal quadriceps force control in anterior cruciate ligament reconstructed patients is related to quadriceps and hamstring muscle dyskinesia

The aim of this study was to determine the effects of anterior cruciate ligament reconstruction (ACLR) on sub-maximal quadriceps force control with respect to quadriceps and hamstring muscle activity. Thirty ACLR individuals together with 30 healthy individuals participated. With real-time visual feedback of muscle force output and electromyographic electrodes attached to the quadriceps and hamstring muscles, subjects performed an isometric knee extension task where they increased and decreased their muscle force output at 0.128 Hz within a range of 5–30% maximum voluntary capacity. The ACLR group completed the task with more error and increased medial hamstring and vastus medialis activation (p < 0.05). Moderate negative correlations (p < 0.05) were observed between quadriceps force control and medial (Spearman’s rho = −0.448, p = 0.022) and lateral (Spearman’s rho = −0.401, p = 0.034) hamstring activation in the ACLR group. Diminished quadriceps sub-maximal force control in ACLR subjects was reflective of medial quadriceps and hamstring dyskinesia (i.e., altered muscle activity patterns and coordination deficits). Within the ACLR group however, augmented hamstring co-activation was associated with better quadriceps force control. Future studies should explore the convergent validity of quadriceps force control in ACLR patients.     

Effect of the contraction of medial rotators of the tibia on the electromyographic activity of vastus medialis and vastus lateralis

PurposeThis study attempted to assess if the resisted contraction of medial rotators of the tibia increases the ratio between the activity of vastus medialis (VM) and vastus lateralis (VL) during maximal isometric contractions (MIC) of the quadriceps femoral (QF) muscle at 90° of knee flexion.MethodsAbout 24 female subjects participated in this study, performing four series MIC of the QF. In the first series subjects performed only MIC of the QF muscle, whereas in the other three there was MIC of the QF with resisted contraction of medial rotators of the tibia, with the tibia positioned in medial, neutral and lateral rotation. During each contraction, VM and VL electromyographic signal (EMGs) and QF force were collected, being the EMGs root mean square (RMS) used to access the activity level of these muscles.ResultsThe use of the General Linear Model (GLM) test showed that for α = 0.05 there was a significant increase in the VM:VL ratio when the resisted contraction of medial rotators of the tibia was performed with the tibia in medial (p = <0.0001), neutral (p = <0.0001) and lateral rotation (p = 0.001). The same test showed that during MIC of the QF associated to resisted contraction of medial rotators of the tibia there were no significant differences in the VM:VL ratio between the three tibial rotation positions adopted (p = 0.866 [medial–neutral]; p = 0.106 [medial–lateral]; p = 0.068 [neutral–lateral]).ConclusionsThe resisted contraction of medial rotators of the tibia increases the VM:VL ratio during MIC of the QF and the tibial rotation position does not influence the VM:VL ratio during MIC associated to resisted contraction of medial rotators of the tibia.     

Voluntary activation of trapezius measured with twitch interpolation

This study investigated the feasibility of measuring voluntary activation of the trapezius muscle with twitch interpolation. Subjects (n = 8) lifted the right shoulder or both shoulders against fixed force transducers. Stimulation of the accessory nerve in the neck was used to evoke maximal twitches in right trapezius. The twitch-like increments in force (superimposed twitches) evoked during different strength voluntary contractions were linearly related to voluntary force (r = ?0.82 to ?0.99). Hence, voluntary activation could be quantified by twitch interpolation with this stimulus. Comparison of unilateral and bilateral MVCs showed that maximal voluntary force was greater in unilateral than bilateral efforts (92.7 ± 2.9% and 82.3 ± 5.8% MVC, respectively) but voluntary activation was similar (88.6 ± 9.6% and 91.7 ± 5.2%). Trapezius is commonly affected in work-related musculoskeletal disorders. Measurement of voluntary activation will be a useful technique to demonstrate whether the reduced maximal voluntary force reported in such disorders is due to muscular or neural factors.     

The influence of myosin heavy chain isoform content on mechanical behavior of the vastus lateralis in vivo

This study examined correlations between type I percent myosin heavy chain isoform content (%MHC) and mechanomyographic amplitude (MMG_RMS) during isometric muscle actions. Fifteen (age = 21.63 ± 2.39) participants performed 40% and 70% maximal voluntary contractions (MVC) of the leg extensors that included increasing, steady force, and decreasing segments. Muscle biopsies were collected and MMG was recorded from the vastus lateralis. Linear regressions were fit to the natural-log transformed MMG_RMS–force relationships (increasing and decreasing segments) and MMG_RMS was selected at the targeted force level during the steady force segment. Correlations were calculated among type I%MHC and the b (slopes) terms from the MMG_RMS–force relationships and MMG_RMS at the targeted force. For the 40% MVC, correlations were significant (P < 0.02) between type I%MHC and the b terms from the increasing (r = −0.804) and decreasing (r = −0.568) segments, and MMG_RMS from the steady force segment (r = −0.606). Type I%MHC was only correlated with MMG_RMS during the steady force segment (P = 0.044, r = −0.525) during the 70% MVC. Higher type I%MHC reduced acceleration in MMG_RMS (b terms) during the 40% MVC and the amplitude during the steady force segments. The surface MMG signal recorded during a moderate intensity contraction provided insight on the contractile properties of the VL in vivo.     

The effectiveness of stretch–shortening cycling in upper-limb extensor muscles during elite cross-country skiing with the double-poling technique

This investigation was designed to evaluate the effectiveness of stretch–shortening cycling (SSC_EFF) in upper-limb extensor muscles while cross-country skiing using the double-poling technique (DP). To this end, SSC_EFF was analyzed in relation to DP velocity and performance. Eleven elite cross-country skiers performed an incremental test to determine maximal DP velocity (V_max). Thereafter, cycle characteristics, elbow joint kinematics and poling forces were monitored on a treadmill while skiing at two sub-maximal and racing velocity (85% of V_max). The average EMG activities of the triceps brachii and latissimus dorsi muscles were determined during the flexion and extension sub-phases of the poling cycle (EMG_FLEX, EMG_EXT), as well as prior to pole plant (EMG_PRE). SSC_EFF was defined as the ratio of aEMG_FLEX to aEMG_EXT. EMG_PRE and EMG_FLEX increased with velocity for both muscles (P < 0.01), as did SSC_EFF (from 0.9 ± 0.3 to 1.3 ± 0.5 for the triceps brachii and from 0.9 ± 0.4 to 1.5 ± 0.5 for the latissimus dorsi) and poling force (from 253 ± 33 to 290 ± 36 N; P < 0.05). Furthermore, SSC_EFF was positively correlated to V_max, to EMG_PRE and EMG_FLEX (P < 0.05). The neuromuscular adaptations made at higher velocities, when more poling force must be applied to the ground, exert a major influence on the DP performance of elite cross-country skiers.     

Muscle architecture variations along the human semitendinosus and biceps femoris (long head) length

The purpose of this study was to examine whether muscle architecture of the long head of biceps femoris (BF) and semitendinosus (ST) muscles varies along their length. The ST and BF muscles were dissected and removed from their origins in eight cadaveric specimens (age range 67.8–73.4 years). One-way analysis of variance designs were used to compare fascicle length (FL), pennation angle (PA) and muscle thickness (MT) between proximal, mid-belly and distal positions. Tendon and muscle length properties were also quantified. For the BF muscle, one-way analysis of variance tests showed a higher PA (23.96 ± 3.82°) and FL (7.12 ± 0.48 cm) proximally than distal positions (PA = 17.78 ± 1.95° and FL = 6.35 ± 0.89 cm, respectively). For the ST, there was a significantly (p < 0.05) lower PA (8.81 ± 1.22°) and FL (13.10 ± 1.54 cm) proximally than distally (PA = 14.69 ± 1.09° and FL = 15.49 ± 2.30 cm, respectively). Muscle thickness significantly increased from distal to more proximal positions (p < 0.05). These data suggest that the ST and BF architecture is not uniform and that measurement of these parameters largely depends on the measurement site. Modeling these muscles by assuming a uniform architecture along muscle length may yield less accurate representation of human hamstring muscle function.     

Primary stability of tibial plateaus under dynamic compression-shear loading in human tibiae – Influence of keel length,cementation area and tibial stem

The objective of our study was to evaluate the impact of the tibial keel & stem length in surface cementation, of a full cemented keel and of an additional tibial stem on the primary stability of a posterior stabilised tibial plateau (VEGA® System Aesculap Tuttlingen, Germany) under dynamic compression-shear loading conditions in human tibiae.We performed the cemented tibial plateau implantations on 24 fresh-frozen human tibiae of a mean donor age of 70.7 years (range 47–97). The tibiae were divided into four groups of matched pairs based on comparable trabecular bone mineral density. To assess the primary stability under dynamic compression shear conditions, a 3D migration analysis of the tibial component relative to the bone based on displacements and deformations and an evaluation of the cement layer including penetration was performed by CT-based 3D segmentation.Within the tested implant fixation principles the mean load to failure of a 28 mm keel and a 12 mm stem (40 mm) was 4700 ± 1149 N and of a 28 mm keel length was 4560 ± 1429 N (p = 0.996), whereas the mean load to failure was 4920 ± 691 N in full cementation (p = 0.986) and 5580 ± 502 N with additional stem (p = 0.537), with no significant differences regarding the dynamic primary stability under dynamic compression-shear test conditions.From our observations, we conclude that there is no significant difference between a 40 mm and a 28 mm tibial keel & stem length and also between a surface and a full cementation in the effect on the primary stability of a posterior stabilised tibial plateau, in terms of failure load, migration characteristics and cement layer thickness including the penetration into the trabecular bone.