Influence of muscle strength, power, and rapid force capacity on maximal club head speed in male national level golfers.

This study investigated the relationships between maximal club head speed (CHS) and physiological and anthropometric parameters in 21 national-level male golfers (age: 21.9 ± 3.9 years; handicap: +1.1 ± 1.7). Maximal isometric strength (MVC) was measured during isometric mid-thigh pull and bench press, while MVC and rate of force development (RFD) were measured during isometric leg press. Power, lower limb stiffness, positive impulse, jump height and RFDdyn were measured during countermovement jump (CMJ). Moreover, rotational trunk power, active range of motion (AROM) and anthropometrics were determined. Comparisons were made between participants with high (FTG) and low (STG) CHS, respectively. FTG demonstrated greater isometric mid-thigh pull and isometric bench press MVC, leg press RFD, rotational trunk power, and CMJ parameters (except RFDdyn) as well as reduced hip AROM compared to STG (P < 0.01). CHS was positively correlated to isometric mid-thigh pull and isometric bench press MVC, leg press RFD, rotational trunk power and CMJ parameters (P < 0.01). In conclusion, strong positive correlations were observed between maximal CHS and maximal strength and power parameters. Consequently, improving maximal neuromuscular strength and power may be considered of importance for golfers, as greater CHS and accompanying driving distance may lead to competitive advantages.

Concurrent validity and intrarater reliability of two ultrasound-based methods for assessing patellar tendon stiffness.

INTRODUCTION: Assessment of tendon stiffness in vivo traditionally involves maximal muscle contractions, which can be challenging in pain populations. Alternative methods are suggested, although the clinimetric properties are sparse. This study investigated the concurrent validity and the intrarater reliability of two ultrasound-based methods for assessing patellar tendon stiffness. METHODS: Patellar tendon stiffness was assessed in 17 healthy adults with (a) the dynamometer and B-mode ultrasonography method (DBUS) and (b) the strain elastography method. Correlations between the two methods were analysed using Kendall's Tau-b. The relative reliability of both methods was evaluated using intraclass correlation coefficient (ICC). The absolute reliability was presented by Bland-Altman plots, standard error of measurement (SEM) and minimum detectable change (MDC). RESULTS: No correlation was found between the two methods, irrespective of reference tissue in strain elastography (Kendall's Tau-b Hoffa = -0.01 (p = 1.00), Kendall's Tau-b subcutis = 0.04 (p = 0.87)). Tracking of the tendon elongation in the DBUS method had good to excellent relative reliability (ICC = 0.95 (95% confidence interval - CI: 0.85-0.98)) and high absolute reliability (SEM = 0.04 mm (1%), MDC = 0.11 mm (3%)). The strain elastography method had good to excellent relative reliability, regardless of reference tissue (ICC Hoffa = 0.95 (95% CI: 0.86-0.98), ICC subcutis = 0.94 (95% CI: 0.82-0.98)), but low absolute reliability (SEM Hoffa = 0.06 (20%), MDC Hoffa = 0.18 (60%), SEM subcutis = 0.12 (41%), MDC subcutis = 0.32 (110%)). CONCLUSIONS: No concurrent validity existed for DBUS and strain elastography, suggesting that the two methods measure different tendon properties. The overall reliability for the DBUS method was high, but the absolute reliability was low for strain elastography stiffness ratios. Therefore, the strain elastography method may not be recommended for tracking differences in patellar tendon stiffness in healthy adults.

Specialized properties of the triceps surae muscle-tendon unit in professional ballet dancers.

This study compared professional ballet dancers (n = 10) to nonstretching controls (n = 10) with the purpose of comparing muscle and tendon morphology, mechanical, neural, and functional properties of the triceps surae and their role for ankle joint flexibility. Torque-angle and torque-velocity data were obtained during passive and active conditions by use of isokinetic dynamometry, while tissue morphology and mechanical properties were evaluated by ultrasonography. Dancers displayed longer gastrocnemius medialis fascicles (55 ± 5 vs 47 ± 6 mm) and a longer (207 ± 33 vs 167 ± 10 mm) and more compliant (230 ± 87 vs 364 ± 106 N/mm) Achilles tendon compared to controls. Greater passive ankle dorsiflexion range of motion (40 ± 7 vs 17 ± 9°) was seen in dancers, resulting from greater fascicle strain and greater elongation of the muscle. Peak electromyographic (EMG) activity recorded during passive stretching was lower in dancers, and at common joint angles, dancers displayed lower EMG amplitude and lower passive joint stiffness. No differences between groups were seen in maximal isometric plantar flexor torque, isokinetic peak torque, angle of peak torque, or work. In conclusion, the greater ankle joint flexibility of professional dancers seems attributed to multiple differences in morphological and mechanical properties of muscle and tendinous tissues, and to factors related to neural activation.

Reliable and sensitive physical testing of elite trapeze sailors.

It was investigated whether a newly developed discipline-specific test for elite-level trapeze sailors is reliable and sensitive. Furthermore, the physical demands of trapeze sailing were examined. In part 1, 9 national team athletes were accustomed to a simulated sailing test, which subsequently was completed on 4 occasions to determine test reliability and sensitivity to manipulations in body weight. Rope-pulling mean power output (MPO), oxygen consumption (VO2 ), heart rate (HR), and blood lactate values were acquired in all trials. In part 2, 6 sailors completed on-water racing with concurrent measurements of VO2 , HR, and blood lactate. VO2max was determined during an incremental treadmill running test. Typical error, minimal difference, and ICC for average MPO in the test were 1.3%, 1.7%, and 0.99%, respectively. Adding 4 kg of external body weight caused a decrease in average MPO (270 ± 45W vs 265 ± 45W, P < .05) and an increase in VO2 (2.44 ± 0.23 L·min-1 vs 2.55 ± 0.26 L·min-1 , P < .01). VO2 , HR, and blood lactate during on-water sailing were 54.5% ± 7.2% VO2max , 75.1% ± 3.1% HRmax , and 5.8 ± 2.7 mmol·L-1 , respectively. However, VO2 and HR were substantially higher for periods of the race as peak values were 83.5% ± 11.4% and 89.9% ± 1.7% of max, respectively. In conclusion, the present test is reliable and sensitive, thus providing a sailing-specific alternative to traditional physical testing of elite trapeze sailors. Additionally, on-water racing requires moderate aerobic energy production, although oxygen consumption can approach maximal levels for short periods of time.

Hiking strap force decreases during sustained upwind sailing.

The hypothesis, that sailing upwind in wind speeds above 12 knots causes fatigue, which manifests as a reduction in exerted hiking strap force and/or maximal isometric voluntary contraction force (MVC) of the knee extensors, was evaluated. Additionally, it was investigated if a relationship exists between maximal exerted hiking force (hMVC) and sailing performance. In part 1 of the study, 12 national level athletes sailed upwind for 2 × 10 min while hiking strap forces were continuously acquired. Before, in between and after sailing periods, the MVC of the knee extensors was measured. In part 2 of the study, hMVC was measured dry land in a hiking bench and correlated with the overall results at a national championship. Hiking strap force decreased from the first to the last minute in both 10 min sailing periods (430 ± 131 vs. 285 ± 130 N, P < .001 and 369 ± 74 vs. 267 ± 97 N, P < .001, respectively), but MVC was similar before, between and after the two 10 min sailing periods (878 ± 215 vs. 852 ± 202 vs. 844 ± 211 130 N). In part 2, a significant positive correlation (r2 = 0.619, P < .01) was observed between hMVC and regatta results. In conclusion, upwind sailing in wind speeds above 12 knots causes sailing-specific fatigue as evidenced by a marked reduction in exerted hiking strap force. However, MVC of the knee extensors was not compromised ∼45 s after hiking was terminated. Additionally, sailing performance is related to maximal hiking force.

Hamstrings functional properties in athletes with high musculo-skeletal flexibility.

The purpose of this study was to examine whether athletes with highly flexible hamstring muscle-tendon units display different passive and contractile mechanical properties compared with controls. Flexibility, passive, and active torque-angle properties were assessed in 21 female elite rhythmic gymnasts and 16 female age-matched athletes. Passive resistance to stretch was measured during knee extension with the hip fixed at 100° of flexion. Concentric isokinetic maximal voluntary knee flexion and extension torques were measured at 60°/s in the same position. Tests of flexibility and passive resistance to stretch indicated a greater flexibility in the gymnasts. Despite no differences between groups in knee flexion and extension peak torque, gymnasts reached knee flexion peak torque at more extended positions (longer muscle lengths) and displayed significantly different torque-angle relations. When active torque was corrected for passive resistance to stretch, differences increased, gymnasts producing more work, and maintaining ≥ 70% of peak torque over a larger range of joint excursion. In conclusion, individuals with a higher flexibility of the hamstrings MTU present a different torque-angle profile, favoring the production of flexion torque toward extended knee positions, displaying larger functional range of motion and a higher mechanical work output during knee flexion.

Physical requirements in Olympic sailing.

Physical fitness and muscular strength are important performance parameters in Olympic sailing although their relative importance changes between classes. The Olympic format consists of eight yacht types combined into 10 so-called events with total 15 sailors (male and female) in a complete national Olympic delegation. The yachts have different requirements with respect to handling, and moreover, each sailor plays a specific role when sailing. Therefore physical demands remain heterogeneous for Olympic sailors. Previous studies have mainly examined sailors where 'hiking' (the task of leaning over the side of the yacht to increase righting moment) is the primary requirement. Other than the ability to sustain prolonged quasi-isometric contractions, hiking seems to require significant maximal muscle strength especially in knee extensors, hip flexors and abdominal and lower back muscles. Another group of studies has investigated boardsailing and provided evidence to show that windsurfing requires very high aerobic and anaerobic capacity. Although data exist on other types of sailors, the information is limited, and moreover the profile of the Olympic events has changed markedly over the last few years to involve more agile, fast and spectacular yachts. The change of events in Olympic sailing has likely added to physical requirements; however, data on sailors in the modern-type yachts are scarce. The present paper describes the recent developments in Olympic sailing with respect to yacht types, and reviews the existing knowledge on physical requirements in modern Olympic sailing. Finally, recommendations for future research in sailing are given.

Ultrasound-based testing of tendon mechanical properties: a critical evaluation.

In the past 20 years, the use of ultrasound-based methods has become a standard approach to measure tendon mechanical properties in vivo. Yet the multitude of methodological approaches adopted by various research groups probably contribute to the large variability of reported values. The technique of obtaining and relating tendon deformation to tensile force in vivo has been applied differently, depending on practical constraints or scientific points of view. Divergence can be seen in 1) methodological considerations, such as the choice of anatomical features to scan and to track, force measurements, or signal synchronization; and 2) in physiological considerations related to the viscoelastic behavior or length measurements of tendons. Hence, the purpose of the present review is to assess and discuss the physiological and technical aspects connected to in vivo testing of tendon mechanical properties. In doing so, our aim is to provide the reader with a qualitative analysis of ultrasound-based techniques. Finally, a list of recommendations is proposed for a number of selected issues.

Influence of loading rate on patellar tendon mechanical properties in vivo.

BACKGROUND: Rate-dependent properties of tendons have consistently been observed in vitro but in vivo studies comparing the effects of loading duration on this feature remain conflicting. The main purpose of the present study was to evaluate whether tendon loading rate per se would affect in vivo tendon mechanical properties. METHODS: Twenty-two physically active male subjects were recruited. Patellar tendon deformation was recorded with ultrasonography under voluntary isometric contractions at rates of 50, 80 and 110Nm/s, controlled via visual feedback. FINDINGS: Subjects were able to accurately generate all three loading rates (Accuracy=2% to 15%), with a greater steadiness at 50 (CV=12.4%) and 110Nm/s (CV=13.1%) than at 80Nm/s (CV=22.9%). Loading rate did not appreciably affect strain or stress. However, stiffness (ɳp(2)=0.555) and Youngs's Modulus (ɳp(2)=0.670) were significantly higher at 80Nm/s (21.4% and 21.6%, respectively) and at 110Nm/s (32.5% and 32.0%, respectively) than at 50Nm/s. Similarly, stiffness and Young's modulus were 9.9% and 8.8% higher, respectively, at 110Nm/s than at 80Nm/s. INTERPRETATION: These results indicate that in vivo measurements of patellar tendon mechanics are influenced by loading rate. Moreover, they bear important methodological implications for in vivo assessment of mechanical properties of this tendon and possibly other human tendons.

Limited difference in time to failure between sustained force and position control contractions with the knee extensors.

Different types of contractile fatiguing tasks ("force/position tasks") have shown that the rate of neuromuscular impairment is task dependent. Whether fatigue resistance is uniform across different types of limb joints is poorly understood because the force-position paradigm has mainly been applied to upper extremity joints under unstable conditions. Therefore, the purpose of the present study was to investigate task dependency in the more stable knee joint. Fourteen subjects performed two sustained isometric knee extensor contractions to failure. In the force task, 20% of maximal voluntary contraction force was maintained for as long as possible with visual feedback of the force, while in the position task, the load was similar, but subjects received visual joint angle feedback. No significant difference was observed in time to failure (force task: 423±61 s, position task: 379±48 s), increase in electromyographic amplitude or perceived exertion between tasks. The force-position paradigm has not been applied previously to the quadriceps, and the difference between the present and the previous results may partly be attributed to joint stability and the volume of co-contracting muscles, such that in addition to the previously noted mechanisms of muscle fatigue, the mechanical design of the relevant joint and muscle actuators may influence task dependency during sustained submaximal contractions.

The effect of passive movement training on angiogenic factors and capillary growth in human skeletal muscle.

The effect of a period of passive movement training on angiogenic factors and capillarization in skeletal muscle was examined. Seven young males were subjected to passive training for 90 min, four times per week in a motor-driven knee extensor device that extended one knee passively at 80 cycles min₋1. The other leg was used as control. Muscle biopsies were obtained from m. v. lateralis of both legs before as well as after 2 and 4 weeks of training. After the training period, passive movement and active exercise were performed with both legs, and muscle interstitial fluid was sampled from microdialysis probes in the thigh. After 2 weeks of training there was a 2-fold higher level of Ki-67 positive cells, co-localized with endothelial cells, in the passively trained leg which was paralleled by an increase in the number of capillaries around a fibre (P <0.05). Capillary density was higher than pre-training at 4 weeks of training (P <0.05). The training induced an increase in the mRNA level of endothelial nitric oxide synthase (eNOS), the angiopoietin receptor Tie-2 and matrix metalloproteinase (MMP)-9 in the passively trained leg and MMP-2 and tissue inhibitor of MMP (TIMP)-1 mRNA were elevated in both legs. Acute passive movement increased (P <0.05) muscle interstitial vascular endothelial growth factor (VEGF) levels 4- to 6-fold above rest and the proliferative effect, determined in vitro, of the muscle interstitial fluid ~16-fold compared to perfusate. The magnitude of increase was similar for active exercise. The results demonstrate that a period of passive movement promotes endothelial cell proliferation and angiogenic factors and initiates capillarization in skeletal muscle.

Use of performance- and image-enhancing substances among recreational athletes: a quantitative analysis of inquiries submitted to the Danish anti-doping authorities.

The use of performance- and image-enhancing drugs/substances (PIED) outside elite sports appears to be increasing, although the current knowledge of the nature of PIED use among recreational athletes is scarce. The present study analyzed enquiries that were submitted to the Danish Anti Doping Agency (ADD) over an 18-month period, to gain knowledge of PIED use among individuals who exercise recreationally in Denmark. One thousand three hundred ninety eight queries were examined with respect to the age and gender of the enquirer, affiliation to sport or exercise and substance in question. The key findings were that the ADD information service is generally used by males in their mid-20s who exercise in gyms and are not engaged in competitive sports. Approximately 15% of the enquirers were users of anabolic androgenic steroids (AAS) or other substances banned within elite sports by the World Anti Doping Agency, and an additional 15% considered using such substances. The present results suggest that there is a pronounced interest in the use of AAS and other PIEDs among Danish gym members.

Novel methods for tendon investigations.

PURPOSE: Tendon structures have been studied for decades, but over the last decade, methodological development and renewed interest for metabolic, circulatory and tissue protein turnover in tendon tissue has resulted in a rising amount of investigations. METHOD: This paper will detail the various modern investigative techniques available to study tendons. RESULTS: There are a variety of investigative methods available to study the correlations between mechanics and biology in tendons. CONCLUSION: The available methodologies not only allow for potential insight into physiological and pathophysiological mechanisms in tendon tissue, but also, to some extent, allow for more elaborate studies of the intact human tendon.

Habitual loading results in tendon hypertrophy and increased stiffness of the human patellar tendon.

The purpose of this study was to examine patellar tendon (PT) size and mechanical properties in subjects with a side-to-side strength difference of > or =15% due to sport-induced loading. Seven elite fencers and badminton players were included. Cross-sectional area (CSA) of the PT obtained from MRI and ultrasonography-based measurement of tibial and patellar movement together with PT force during isometric contractions were used to estimate mechanical properties of the PT bilaterally. We found that distal tendon and PT, but not mid-tendon, CSA were greater on the lead extremity compared with the nonlead extremity (distal: 139 +/- 11 vs. 116 +/- 7 mm(2); mid-tendon: 85 +/- 5 vs. 77 +/- 3 mm(2); proximal: 106 +/- 7 vs. 83 +/- 4 mm(2); P < 0.05). Distal tendon CSA was greater than proximal and mid-tendon CSA on both the lead and nonlead extremity (P < 0.05). For a given common force, stress was lower on the lead extremity (52.9 +/- 4.8 MPa) compared with the nonlead extremity (66.0 +/- 8.0 MPa; P < 0.05). PT stiffness was also higher in the lead extremity (4,766 +/- 716 N/mm) compared with the nonlead extremity (3,494 +/- 446 N/mm) (P < 0.05), whereas the modulus did not differ (lead 2.27 +/- 0.27 GPa vs. nonlead 2.16 +/- 0.28 GPa) at a common force. These data show that a habitual loading is associated with a significant increase in PT size and mechanical properties.

Effect of habitual exercise on the structural and mechanical properties of human tendon, in vivo, in men and women.

We examined whether long-term habitual training (a) was associated with differences in structural and mechanical properties in tendon in women and (b) yielded different tendon properties in men and women. Ten male runners, 10 female runners and 10 female non-runners were tested. Tendon cross-sectional area (CSA) and length of the patellar and Achilles tendon were determined with MRI. Ultrasonography-based measurement of tendon elongation and force during isometric contractions provided mechanical properties. Distal patellar and Achilles tendon CSAs were greater than the proximal part in all three groups (P<0.05). Weight-normalized Achilles tendon CSA were similar in trained (2.78+/-0.17 mm(2)/kg(3/4)) and untrained women (2.60+/-0.13 mm(2)/kg(3/4)), while that in trained men (3.77+/-0.27 mm(2)/kg(3/4)) was greater compared with trained women (P<0.01). Patellar tendon CSA were comparable in trained and untrained women, while that in trained men was greater compared with trained women (P<0.01). Patellar tendon stiffness was greater in male runners (3528+/-773 N/mm) compared with female runners (2069+/-666 N/mm) and non-runners (2477+/-381 N/mm), (P<0.01), but patellar tendon deformation, stress, strain and modulus were similar. These data indirectly suggest that the ability of Achilles and patellar tendons to adapt in response to habitual loading such as running is attenuated in women.

Passive knee joint range of motion is unrelated to the mechanical properties of the patellar tendon.

The physiological factors that govern passive joint range of motion (ROM) are poorly understood. The present study investigated the relation between passive knee joint ROM and the mechanical properties of the patellar tendon. Knee joint ROM was assessed in 43 individuals, and the subjects with the greatest ROM (flexible group, n=10) and lowest ROM (inflexible group, n=10) were selected for further analysis. In these groups an overall "lower extremity joint ROM score" was determined with 11 clinical tests. The elongation of the patellar tendon was assessed during graded maximal isometric knee extensor contractions using ultrasonography, and the mechanical properties of the patellar tendon were determined from corresponding load and tendon deformation data. The two groups were similar with respect to weight, height, tendon cross-sectional area and length, and were, furthermore, equally physically active. The knee joint ROM and lower extremity joint ROM score was significantly different between the groups (flexible: 136+/-7 degrees vs inflexible: 76+/-16 degrees , P<0.001 and flexible: -4.7+/-1.3 vs inflexible: 3.1+/-4.1, P<0.001). There was no difference between groups in maximal knee extensor force or the corresponding tendon deformation. The tendon stiffness (flexible: 3269+/-1591 vs inflexible: 3185+/-1457 N/mm), stress (flexible: 22.4+/-6.5 vs inflexible: 34.0+/-17.6 N/mm(2)), strain (flexible; 6.5+/-1.6 vs inflexible: 7.2+/-1.9%) and Young's modulus (flexible: 0.81+/-0.35 vs inflexible: 1.22+/-0.52 GPa) were not different between the two groups of subjects. These data suggest that differences in knee joint ROM cannot be explained by the mechanical properties of the patellar tendon.

Low-intensity tensile loading increases intratendinous glucose uptake in the Achilles tendon.

The metabolic activity of tendinous tissues has traditionally been considered to be of limited magnitude. However, recent studies have suggested that glucose uptake increases in the force-transmitting tissues as a response to contractile loading, which in turn indicates an elevated tissue metabolism. The purpose of the present study was to investigate whether such a mechanism could be observed for the human Achilles tendon following tensile loading. Six subjects participated in the study. Unilateral Achilles tendon loading was applied by 25-min intermittent voluntary plantar flexor contractions. A radioactive tracer ([18F]-2-fluoro-2-deoxy-D-glucose) was administered during muscle action, and glucose uptake was measured by use of PET. Regions of interest were defined on the PET images corresponding to the cross section of Achilles tendon at two longitudinally separated sites (insertion and free tendon). Glucose uptake index was determined within respective regions of interest for the active and resting leg. Tendon force during voluntary contractions was approximately 13% of maximal voluntary contraction force. Tendon loading induced an elevated glucose uptake index compared with that of the contralateral resting tendon in the region of tendon insertion (0.13 +/- 0.05 vs. 0.09 +/- 0.02; P < 0.05) and at the free tendon (0.12 +/- 0.01 vs. 0.08 +/- 0.02; P < 0.05). The present data suggest that tissue metabolism is elevated in the human Achilles tendon in response to low-intensity loading.

Mechanical properties of the human patellar tendon, in vivo.

BACKGROUND: Mechanical properties of the human patellar tendon are largely based on cadaver studies, which may not necessarily be applicable to the human patellar tendon, in vivo. While ultrasonography is an attractive non-invasive method for studying human, in vivo, muscle-tendon behaviour, it has mostly been used to examine Achilles tendon properties. We examine the accuracy of human patellar tendon elongation, in vivo, and its within-day and between-day reproducibility. METHODS: Subjects performed four maximal 10-s ramp isometric knee extension trials to examine within-day reproducibility, and the procedure was repeated on a separate day to assess between-day reproducibility. Continuous and simultaneous ultrasonography based measurement of both tibial and patellar movement together with patellar tendon force yielded mechanical estimates. RESULTS: Longitudinal tibial displacement corresponded to 45 (SEM 8) % of the overall tibia-patella displacement. For within-day reproducibility there was no difference between trials for stiffness [trial a, 4334 (SEM 562) N/mm; trial b, 4273 (SEM 533) N/mm], strain [trial a, 6.9 (SEM 0.6) %; trial b, 6.8 (SEM 0.7) %] or elastic modulus [trial a, 1.09 (SEM 0.12) GPa; trial b, 1.09 (SEM 0.10) GPa]. The within day correlation coefficient and typical error were 0.95 and 9.9% for stiffness, 0.97 and 5.5% for strain, and 0.94 and 9.4% for elastic modulus. The corresponding values for between days were 0.94 and 8.7% for stiffness, 0.98 and 3.7% for strain, and 0.86 and 9.6% for elastic modulus. INTERPRETATION: The present methodology of assessing human patellar tendon elongation, strain and stiffness, in vivo, is accurate and reproducible which permits its use in future investigations of patellar tendon biomechanics and the potential effects of various interventions.

Measuring mechanical properties of the vastus lateralis tendon-aponeurosis complex in vivo by ultrasound imaging.

The mechanical properties of the human vastus lateralis (VL) tendon-aponeurosis complex were investigated in eight male subjects. Knee extensor force, knee joint angle, and corresponding longitudinal VL aponeurosis displacement were monitored synchronously during graded (10-s) maximal isometric knee extension contractions. Displacement observed during isometric conditions may be regarded as an expression of deformation in the tissues distal to the measurement site. Furthermore, aponeurosis displacement was measured during passive knee extension (90-75 degrees degrees ), and used to correct displacement values obtained during active contraction for joint angular motion. The passive trial yielded a highly linear relationship between aponeurosis displacement and joint angular motion (r2 = 0.998 +/- 0.002) with a mean correction factor of 0.41 +/- 0.10 mm/degree. Maximal knee extensor force was 5834 +/- 1341 N with a corresponding VL aponeurosis displacement of 12.7 +/- 2.5 mm, while correcting for joint angular motion reduced maximal displacement approximately 9% (to 11.6 +/- 2.5 mm, P < 0.005) (data presented as means +/- SD). Two separate graded contraction trials were performed, and no between-trial differences were observed in either maximal force or maximal displacement. Between trial coefficient of determination and CV for maximal force and maximal displacement were r2 = 0.97, CV = 2.9% and r2 = 0.92, CV = 4.6%, respectively, indicating intra-day reproducibility of measurements. These data demonstrate that when applying the newly established ultrasound-based method of investigating quadriceps connective tissue mechanical properties, maximal isometric contraction is inevitably associated with some joint angular motion that significantly influences the calculations.

Differential strain patterns of the human gastrocnemius aponeurosis and free tendon, in vivo.

AIM: The mechanical characteristics of the human free tendon and aponeurosis, in vivo, remains largely unknown. The present study evaluated the longitudinal displacement of the separate free Achilles tendon and distal (deep) aponeurosis of the medial gastrocnemius muscle during voluntary isometric contraction. METHODS: Ultrasonography-obtained displacement of the free tendon and tendon-aponeurosis complex, electromyography of the gastrocnemius, soleus, and dorsiflexor muscles, and joint angular rotation were recorded during isometric plantarflexion (n = 5). Tendon cross-sectional area, moment arm and segment lengths (L(o)) were measured using magnetic resonance imaging. Tendon force was calculated from joint moments and tendon moment arm, and stress was obtained by dividing force by cross-sectional area. The difference between the free tendon and tendon-aponeurosis complex deformation yielded separate distal aponeurosis deformation. Longitudinal aponeurosis and tendon strain were obtained from the deformations normalized to segment lengths. RESULTS: At a common tendon force of 2641 +/- 306 N, the respective deformation and Lo were 5.85 +/- 0.85 and 74 +/- 0.8 mm for the free tendon and 2.12 +/- 0.64 and 145 +/- 1.3 mm for the distal aponeurosis, P < 0.05. Longitudinal strain was 8.0 +/- 1.2% for the tendon and 1.4 +/- 0.4% for the aponeurosis, P < 0.01. Stiffness and stored energy was 759 +/- 132 N mm(-1) and 6.14 +/- 1.89 J, respectively, for the free tendon. Cross-sectional area of the Achilles tendon was 73 +/- 4 mm2, yielding a stress of 36.5 +/- 4.6 MPa and Young's modulus of 788 +/- 181 MPa. CONCLUSION: The free Achilles tendon demonstrates greater strain compared with that of the distal (deep) aponeurosis during voluntary isometric contraction, which suggests that separate functional roles may exist during in vivo force transmission.