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This study compared the muscle and tendon morphology of an extraordinarily strong individual, a World's Strongest Man and deadlift champion (WSM), with that of various other athletic, trained, and untrained populations. The WSM completed the following: 1 ) 3.0-T MRI scans, to determine the volume of 22 individual lower limb muscles, 5 functional muscle groups, patellar tendon (PT) cross-sectional area (CSA), and PT moment arm; and 2 ) countermovement jumps (CMJ) and isometric midthigh pull (IMTP) contractions. The WSM was compared with previously assessed groups from our laboratory (muscle and tendon) and the wider research literature (CMJ and IMTP). The WSM's CMJ peak power (9,866 W) and gross (9,171 N) and net (7,480 N) IMTP peak forces were higher than any previously published values. The WSM's overall measured leg muscle volume was approximately twice that of untrained controls (+96%) but with pronounced anatomical variability in the extent of muscular development. The plantar flexor group (+120%) and the guy rope muscles (sartorius, gracilis, and semitendinosus: +140% to +202%), which stabilize the pelvis and femur, demonstrated the largest differences relative to that of untrained controls. The WSM's pronounced quadriceps size (greater than or equal to twofold vs. untrained) was accompanied by modest PT moment arm differences and, notably, was not matched by an equivalent difference in PT CSA (+30%). These results provide novel insight into the musculotendinous characteristics of an extraordinarily strong individual, which may be toward the upper limit of human variation, such that the WSM's very pronounced lower limb muscularity also exhibited distinct anatomical variability and with muscle size largely uncoupled from tendon size. NEW & NOTEWORTHY Lower-body muscle size of an extraordinarily strong individual, a World's Strongest Man and deadlift champion (WSM), was approximately twice that of controls but was underpinned by pronounced anatomical variability in the extent of muscular development (+23-202%): the plantar flexor group and guy rope muscles demonstrating the largest differences. The WSM's quadriceps size (more than or equal to twice that of controls) contrasted with modest differences in patella tendon moment arm (+18%) and was uncoupled from patellar tendon size (+30%).

Introduction: The hamstring muscles play a crucial role in sprint running but are also highly susceptible to strain injuries, particularly within the biceps femoris long head (BFlh). This study compared the adaptations in muscle size and strength of the knee flexors, as well as BFlh muscle and aponeurosis size, after two eccentrically focused knee flexion training regimes: Nordic hamstring training (NHT) vs lengthened state eccentric training (LSET, isoinertial weight stack resistance in an accentuated hip-flexed position) vs habitual activity (no training controls: CON)., Methods: Forty-two healthy young males completed 34 sessions of NHT or LSET over 12 wk or served as CON ( n = 14/group). Magnetic resonance imaging-measured muscle volume of seven individual knee flexors and BFlh aponeurosis area, and maximum knee flexion torque during eccentric, concentric, and isometric contractions were assessed pre- and post-training., Results: LSET induced greater increases in hamstrings (+18% vs +11%) and BFlh (+19% vs +5%) muscle volumes and BFlh aponeurosis area (+9% vs +3%) than NHT (all P ≤ 0.001), with no changes after CON. There were distinctly different patterns of hypertrophy between the two training regimes, largely due to the functional role of the muscles; LSET was more effective for increasing the size of knee flexors that also extend the hip (2.2-fold vs NHT), whereas NHT increased the size of knee flexors that do not extend the hip (1.9-fold vs LSET; both P ≤ 0.001). Changes in maximum eccentric torque differed only between LSET and CON (+17% vs +4%; P = 0.009), with NHT (+11%) inbetween., Conclusions: These results suggest that LSET is superior to NHT in inducing overall hamstrings and BFlh hypertrophy, potentially contributing to better sprint performance improvements and protection against hamstring strain injuries than NHT., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.)

Biceps femoris long head (BF LH ) aponeurosis size was compared between legs with and without prior hamstring strain injury (HSI) using two approaches: within-group (injured vs. uninjured legs of previous unilateral HSI athletes) and between-group (previously injured legs of HSI athletes vs. legs of No Prior HSI athletes). MRI scans were performed on currently healthy, competitive male athletes with Prior HSI history ( n =23;≥1 verified BF LH injury; including a sub-group with unilateral HSI history; most recent HSI 1.6±1.2 years ago) and pair-matched athletes with No Prior HSI history ( n =23). Anonymized axial images were manually segmented to quantify BF LH aponeurosis and muscle size. Prior unilateral HSI athletes' BF LH aponeurosis maximum width, aponeurosis area, and aponeurosis:muscle area ratio were 14.0-19.6% smaller in previously injured vs. contralateral uninjured legs (paired t-test, 0.008≤P≤0.044). BF LH aponeurosis maximum width and area were also 9.4-16.5% smaller in previously injured legs ( n =28) from Prior HSI athletes vs. legs ( n =46) of No Prior HSI athletes (unpaired t-test, 0.001≤P≤0.044). BF LH aponeurosis size was smaller in legs with prior HSI vs. those without prior HSI. These findings suggest BF LH aponeurosis size, especially maximum width, could be a potential cause or consequence of HSI, with prospective evidence needed to support or refute these possibilities., Competing Interests: The authors declare that there is no conflict of interest and that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation., (Thieme. All rights reserved.)

There is a marked difference between males and females in sprint running performance, yet a comprehensive investigation of sex differences in the muscle morphology of sprinters, which could explain the performance differences, remains to be completed. This study compared muscle volumes of 23 individual leg muscles and 5 functional muscle groups, assessed with 3 T magnetic resonance imaging, between male ( n = 31) and female ( n = 22) sprinters, as well as subgroups of elite males (EM, n = 5), elite females (EF, n = 5), and performance-matched (to elite females) males (PMM EF , n = 6). Differences in muscle volume distribution between EM, EF, and unathletic male (UM) controls were also assessed. For the full cohorts, male sprinters were more muscular than their female counterparts, but the differences were nonuniform and anatomically variable, with the largest differences in the hip extensors and flexors. However, among elite sprinters the sex differences in the volume of the functional muscle groups were almost uniform (absolute volume +47-53%), and the muscle volume distribution of EM was more similar to EF than to UM ( P < 0.039). For PMM EF , relative hip extensor volume, but not stature or percent body fat, differentiated for performance (PMM EF and EF < EM) rather than sex. In conclusion, although the full cohorts of sprinters showed a marked sex difference in the amount and distribution of muscle mass, elite sprinters appeared to be selected for a common muscle distribution phenotype that for these elite subgroups was a stronger effect than that of sex. Relative hip extensor muscle volume, rather than stature, percent body fat, or total relative muscle volume, appeared to be the primary determinant of the sex difference in performance. NEW & NOTEWORTHY We present novel evidence suggesting muscle volume, specifically relative hip extensor volume, may be a primary deterministic variable for the sex difference in sprint performance, such that with matched sprint times, male and female sprinters may be expected to have equivalent muscle morphology. We highlight striking similarities in distribution of leg muscle mass between elite male and female sprinters and provide evidence for the existence of a muscular distribution phenotype specific to elite sprinters, irrespective of sex.

Purpose: Collagen peptide supplementation has been reported to enhance synthesis rates or growth in a range of musculoskeletal tissues and could enhance tendinous tissue adaptations to resistance training (RT). This double-blind placebo-controlled study aimed to determine if tendinous tissue adaptations, size (patellar tendon cross-sectional area (CSA) and vastus lateralis (VL) aponeurosis area), and mechanical properties (patellar tendon), after 15 wk of RT, could be augmented with collagen peptide (CP) versus placebo (PLA) supplementation., Methods: Young healthy recreationally active men were randomized to consume either 15 g of CP ( n = 19) or PLA ( n = 20) once every day during a standardized program of lower-body RT (3 times a week). Measurements pre- and post-RT included patellar tendon CSA and VL aponeurosis area (via magnetic resonance imaging), and patellar tendon mechanical properties during isometric knee extension ramp contractions., Results: No between-group differences were detected for any of the tendinous tissue adaptations to RT (ANOVA group-time, 0.365 ≤ P ≤ 0.877). There were within-group increases in VL aponeurosis area (CP, +10.0%; PLA, +9.4%), patellar tendon stiffness (CP, +17.3%; PLA, +20.9%) and Young's modulus (CP, +17.8%; PLA, +20.6%) in both groups (paired t -tests (all), P ≤ 0.007). There were also within-group decreases in patellar tendon elongation (CP, -10.8%; PLA, -9.6%) and strain (CP, -10.6%; PLA, -8.9%) in both groups (paired t -tests (all), P ≤ 0.006). Although no within-group changes in patellar tendon CSA (mean or regional) occurred for CP or PLA, a modest overall time effect ( n = 39) was observed for mean (+1.4%) and proximal region (+2.4%) patellar tendon CSA (ANOVA, 0.017 ≤ P ≤ 0.048)., Conclusions: In conclusion, CP supplementation did not enhance RT-induced tendinous tissue remodeling (either size or mechanical properties) compared with PLA within a population of healthy young men., (Copyright © 2023 by the American College of Sports Medicine.)

Introduction: A paucity of research exists examining the importance of muscle morphological and functional characteristics for elite female sprint performance., Purpose: This study aimed to compare lower body muscle volumes and vertical jumping power between elite and subelite female sprinters and assess the relationships of these characteristics with sprint race and acceleration performance., Methods: Five elite (100 m seasons best [SBE 100 ], 11.16 ± 0.06 s) and 17 subelite (SBE 100 , 11.84 ± 0.42 s) female sprinters underwent: 3T magnetic resonance imaging to determine the volume of 23 individual leg muscles/compartments and five functional muscle groups; countermovement jump and 30 m acceleration tests., Results: Total absolute lower body muscle volume was higher in elite versus subelite sprinters (+15%). Elite females exhibited greater muscle volume of the hip flexors (absolute, +28%; relative [to body mass], +19%), hip extensors (absolute, +22%; relative, +14%), and knee extensors (absolute, +21%), demonstrating pronounced anatomically specific muscularity, with relative hip flexor volume alone explaining 48% of sprint performance variability. The relative volume of five individual muscles (sartorius, gluteus maximus, adductor magnus, vastus lateralis, illiopsoas) were both distinct between groups (elite > subelite) and related to SBE 100 ( r = 0.553-0.639), with the combination of the sartorius (41%) and the adductor magnus (17%) explaining 58% of the variance in SBE 100 . Elite female sprinters demonstrated greater absolute countermovement jump power versus subelite, and absolute and relative power were related to both SBE 100 ( r = -0.520 to -0.741) and acceleration performance ( r = 0.569 to 0.808)., Conclusions: This investigation illustrates the distinctive, anatomically specific muscle volume distribution that facilitates elite sprint running in females, and emphasizes the importance of hip flexor and extensor relative muscle volume., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.)

The purpose of this cross-sectional study was to compare explosive strength and underpinning contractile, hypertrophic, and neuromuscular activation characteristics of long-term maximum strength-trained (LT-MST; ie, ≥3 years of consistent, regular knee extensor training) and untrained individuals. Sixty-three healthy young men (untrained [UNT] n = 49, and LT-MST n = 14) performed isometric maximum and explosive voluntary, as well as evoked octet knee extension contractions. Torque, quadriceps, and hamstring surface EMG were recorded during all tasks. Quadriceps anatomical cross-sectional area (QACSA MAX ; via MRI) was also assessed. Maximum voluntary torque (MVT; +66%) and QACSA MAX (+54%) were greater for LT-MST than UNT ([both] p < 0.001). Absolute explosive voluntary torque (25-150 ms after torque onset; +41 to +64%; [all] p < 0.001; 1.15≤ effect size [ES]≤2.36) and absolute evoked octet torque (50 ms after torque onset; +43, p < 0.001; ES = 3.07) were greater for LT-MST than UNT. However, relative (to MVT) explosive voluntary torque was lower for LT-MST than UNT from 100 to 150 ms after contraction onset (-11% to -16%; 0.001 ≤ p ≤ 0.002; 0.98 ≤ ES ≤ 1.11). Relative evoked octet torque 50 ms after onset was lower (-10%; p < 0.001; ES = 1.14) and octet time to peak torque longer (+8%; p = 0.001; ES = 1.18) for LT-MST than UNT indicating slower contractile properties, independent from any differences in torque amplitude. The greater absolute explosive strength of the LT-MST group was attributable to higher evoked explosive strength, that in turn appeared to be due to larger quadriceps muscle size, rather than any differences in neuromuscular activation. In contrast, the inferior relative explosive strength of LT-MST appeared to be underpinned by slower intrinsic/evoked contractile properties., (© 2022 The Authors. Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.)

Purpose: This study aimed to determine the best muscle size index of muscle strength by establishing if incorporating muscle architecture measurements improved the human muscle size-strength relationship. The influence of calculating muscle force and the location of anatomical cross-sectional area (ACSA) measurements on this relationship were also examined., Methods: Fifty-two recreationally active men completed unilateral isometric knee extension strength assessments and magnetic resonance imaging scans of the dominant thigh and knee to determine quadriceps femoris size variables (ACSA along the length of the femur, maximum ACSA (ACSAMAX), and volume (VOL)) and patellar tendon moment arm. Ultrasound images (two sites per constituent muscle) were analyzed to quantify muscle architecture (fascicle length, pennation angle) and, when combined with VOL (from magnetic resonance imaging), facilitated calculation of quadriceps femoris effective PCSA (EFFPCSA) as potentially the best muscle size determinant of strength. Muscle force was calculated by dividing maximum voluntary torque by the moment arm and addition of antagonist torque (derived from hamstring EMG)., Results: The associations of EFFPCSA (r = 0.685), ACSAMAX (r = 0.697), or VOL (r = 0.773) with strength did not differ, although qualitatively VOL explained 59.8% of the variance in strength, ~11%-13% greater than EFFPCSA or ACSAMAX. All muscle size variables had weaker associations with muscle force than maximum voluntary torque. The association of strength-ACSA at 65% of femur length (r = 0.719) was greater than for ACSA measured between 10%-55% and 75%-90% (r = -0.042-0.633) of femur length., Conclusions: In conclusion, using contemporary methods to assess muscle architecture and calculate EFFPCSA did not enhance the muscle strength-size association. For understanding/monitoring muscle size, the major determinant of strength, these findings support the assessment of muscle volume, which is independent of architecture measurements and was most highly correlated with strength., (Copyright © 2021 by the American College of Sports Medicine.)

This study compared elbow flexor (EF; experiment 1 ) and knee extensor (KE; experiment 2 ) maximal compound action potential (M max ) amplitude between long-term resistance trained (LTRT; n = 15 and n = 14, 6 ± 3 and 4 ± 1 yr of training) and untrained (UT; n = 14 and n = 49) men, and examined the effect of normalizing electromyography (EMG) during maximal voluntary torque (MVT) production to M max amplitude on differences between LTRT and UT. EMG was recorded from multiple sites and muscles of EF and KE, M max was evoked with percutaneous nerve stimulation, and muscle size was assessed with ultrasonography (thickness, EF) and magnetic resonance imaging (cross-sectional area, KE). Muscle-electrode distance (MED) was measured to account for the effect of adipose tissue on EMG and M max . LTRT displayed greater MVT (+66%-71%, P < 0.001), muscle size (+54%-56%, P < 0.001), and M max amplitudes (+29%-60%, P ≤ 0.010) even when corrected for MED ( P ≤ 0.045). M max was associated with the size of both muscle groups ( r  ≥ 0.466, P ≤ 0.011). Compared with UT, LTRT had higher absolute voluntary EMG amplitude for the KE ( P < 0.001), but not the EF ( P = 0.195), and these differences/similarities were maintained after correction for MED; however, M max normalization resulted in no differences between LTRT and UT for any muscle and/or muscle group ( P ≥ 0.652). The positive association between M max and muscle size, and no differences when accounting for peripheral electrophysiological properties (EMG/M max ), indicates the greater absolute voluntary EMG amplitude of LTRT might be confounded by muscle morphology, rather than providing a discrete measure of central neural activity. This study therefore suggests limited agonist neural adaptation after LTRT. NEW & NOTEWORTHY In a large sample of long-term resistance-trained individuals, we showed greater maximal M-wave amplitude of the elbow flexors and knee extensors compared with untrained individuals, which appears to be at least partially mediated by differences in muscle size. The lack of group differences in voluntary EMG amplitude when normalized to maximal M-wave suggests that differences in muscle morphology might impair interpretation of voluntary EMG as an index of central neural activity.

Purpose: Neural drive and contractile properties are well-defined physiological determinants of explosive strength, the influence of muscle architecture and related morphology on explosive strength is poorly understood. The aim of this study was to examine the relationships between Quadriceps muscle architecture (pennation angle [Θ P ] and fascicle length [F L ]) and size (e.g., volume; Q VOL ), as well as patellar tendon moment arm (PT MA ) with voluntary and evoked explosive knee extension torque in 53 recreationally active young men., Method: Following familiarisation, explosive voluntary torque at 50 ms intervals from torque onset (T 50 , T 100 , T 150 ), evoked octet at 50 ms (8 pulses at 300-Hz; evoked T 50 ), as well as maximum voluntary torque, were assessed on two occasions with isometric dynamometry. B-mode ultrasound was used to assess Θ P and F L at ten sites throughout the quadriceps (2-3 sites) per constituent muscle. Muscle size (Q VOL ) and PT MA were quantified using 1.5 T MRI., Result: There were no relationships with absolute early phase explosive voluntary torque (≤ 50 ms), but θ P (weak), Q VOL (moderate to strong) and PT MA (weak) were related to late phase explosive voluntary torque (≥ 100 ms). Regression analysis revealed only Q VOL was an independent variable contributing to the variance in T 100 (34%) and T 150 (54%). Evoked T 50 was also related to Q VOL and θ P. When explosive strength was expressed relative to MVT there were no relationships observed., Conclusion: It is likely that the weak associations of θ P and PT MA with late phase explosive voluntary torque was via their association with MVT/Q VOL rather than as a direct determinant.

Purpose: This study aimed to investigate the differences in muscle volumes and strength between male elite sprinters, sub-elite sprinters, and untrained controls and to assess the relationships of muscle volumes and strength with sprint performance., Methods: Five elite sprinters (100-m season's best equivalent [SBE100], 10.10 ± 0.07 s), 26 sub-elite sprinters (SBE100, 10.80 ± 0.30 s), and 11 untrained control participants underwent 1) 3-T magnetic resonance imaging scans to determine the volume of 23 individual lower limb muscles/compartments and 5 functional muscle groups and 2) isometric strength assessment of lower body muscle groups., Results: Total lower body muscularity was distinct between the groups (controls < sub-elite +20% < elite +48%). The hip extensors exhibited the largest muscle group differences/relationships (elite, +32% absolute and +15% relative [per kg] volume, vs sub-elite explaining 31%-48% of the variability in SBE100), whereas the plantarflexors showed no differences between sprint groups. Individual muscle differences showed pronounced anatomical specificity (elite vs sub-elite absolute volume range, +57% to -9%). Three hip muscles were consistently larger in elite vs sub-elite (tensor fasciae latae, sartorius, and gluteus maximus; absolute, +45%-57%; relative volume, +25%-37%), and gluteus maximus volume alone explained 34%-44% of the variance in SBE100. The isometric strength of several muscle groups was greater in both sprint groups than controls but similar for the sprint groups and not related to SBE100., Conclusions: These findings demonstrate the pronounced inhomogeneity and anatomically specific muscularity required for fast sprinting and provides novel, robust evidence that greater hip extensor and gluteus maximus volumes discriminate between elite and sub-elite sprinters and are strongly associated with sprinting performance., (Copyright © 2020 by the American College of Sports Medicine.)

The greater muscular strength of long-term resistance-trained (LTT) individuals is often attributed to hypertrophy, but the role of other factors, notably maximum voluntary specific tension (ST), muscle architecture, and any differences in joint mechanics (moment arm), have not been documented. The aim of the present study was to examine the musculoskeletal factors that might explain the greater quadriceps strength and size of LTT vs. untrained (UT) individuals. LTT ( n = 16, age 21.6 ± 2.0 yr) had 4.0 ± 0.8 yr of systematic knee extensor heavy-resistance training experience, whereas UT ( n = 52; age 25.1 ± 2.3 yr) had no lower-body resistance training experience for >18 mo. Knee extension dynamometry, T1-weighted magnetic resonance images of the thigh and knee, and ultrasonography of the quadriceps muscle group at 10 locations were used to determine quadriceps: isometric maximal voluntary torque (MVT), muscle volume (Q VOL ), patella tendon moment arm (PTMA), pennation angle (QΘ P ) and fascicle length (QF L ), physiological cross-sectional area (QPCSA), and ST. LTT had substantially greater MVT (+60% vs. UT, P < 0.001) and Q VOL (+56%, P < 0.001) and QPCSA (+41%, P < 0.001) but smaller differences in ST (+9%, P < 0.05) and moment arm (+4%, P < 0.05), and thus muscle size was the primary explanation for the greater strength of LTT. The greater muscle size (volume) of LTT was primarily attributable to the greater QPCSA (+41%; indicating more sarcomeres in parallel) rather than the more modest difference in F L (+11%; indicating more sarcomeres in series). There was no evidence in the present study for regional hypertrophy after LTT. NEW & NOTEWORTHY Here we demonstrate that the larger muscle strength (+60%) of a long-term (4+ yr) resistance-trained group compared with untrained controls was due to their similarly larger muscle volume (+56%), primarily due to a larger physiological cross-sectional area and modest differences in fascicle length, as well as modest differences in maximum voluntary specific tension and patella tendon moment arm. In addition, the present study refutes the possibility of regional hypertrophy, despite large differences in muscle volume.

The purpose of this study was to compare the effect of resistance training (RT) duration, including years of exposure, on agonist and antagonist neuromuscular activation throughout the knee extension voluntary torque range. Fifty-seven healthy men (untrained [UNT] n = 29, short-term RT [12WK] n = 14, and long-term RT [4YR] n = 14) performed maximum and sub-maximum (20%-80% maximum voluntary torque [MVT]) unilateral isometric knee extension contractions with torque, agonist and antagonist surface EMG recorded. Agonist EMG, including at MVT, was corrected for the confounding effects of adiposity (ie, muscle-electrode distance; measured with ultrasonography). Quadriceps maximum anatomical cross-sectional area (QACSA MAX ; via MRI) was also assessed. MVT was distinct for all three groups (4YR +60/+39% vs UNT/12WK; 12WK +15% vs UNT; 0.001 < P ≤ 0.021), and QACSA MAX was greater for 4YR (+50/+42% vs UNT/12WK; [both] P < 0.001). Agonist EMG at MVT was +44/+33% greater for 4YR /12WK ([both] P < 0.001) vs. UNT, but did not differ between RT groups. The torque-agonist EMG relationship of 4YR displayed a right/down shift with lower agonist EMG at the highest common torque (196 Nm) compared to 12WK and UNT (0.005 ≤ P ≤ 0.013; Effect size [ES] 0.90 ≤ ES ≤ 1.28). The torque-antagonist EMG relationship displayed a lower slope with increasing RT duration (4YR < 12WK < UNT; 0.001 < P ≤ 0.094; 0.56 ≤ ES ≤ 1.31), and antagonist EMG at the highest common torque was also lower for 4YR than UNT (-69%; P < 0.001; ES = 1.18). In conclusion, 4YR and 12WK had similar agonist activation at MVT and this adaptation may be maximized during early months of RT. In contrast, inter-muscular coordination, specifically antagonist coactivation was progressively lower, and likely continues to adapt, with prolonged RT., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Voluntary surface electromyography (sEMG) amplitude is known to be influenced by both electrode position and subcutaneous adipose tissue thickness, and these factors likely compromise both between- and within-individual comparisons. Normalization of voluntary sEMG amplitude to evoked maximum M-wave parameters (M MAX peak-to-peak [P-P] and Area) may remove the influence of electrode position and subcutaneous tissue thickness. The purpose of this study was to: (a) assess the influence of electrode position on voluntary, evoked (M MAX P-P and Area), and normalized sEMG measurements across the surface of the vastus lateralis (VL; experiment 1: n = 10); and (b) investigate if M MAX normalization removes the confounding influence of subcutaneous tissue thickness [muscle-electrode distance (MED) from ultrasound imaging] on sEMG amplitude (experiment 2; n = 41). Healthy young men performed maximum voluntary contractions (MVCs) and evoked twitch contractions during both experiments. Experiment 1: voluntary sEMG during MVCs was influenced by electrode location (P ≤ 0.046, ES≥1.49 "large"), but when normalized to M MAX P-P showed no differences between VL sites (P = 0.929) which was not the case when normalized to M MAX Area (P < 0.004). Experiment 2: voluntary sEMG amplitude was related to MED, which explained 31%-38% of the variance. Normalization of voluntary sEMG amplitude to M MAX P-P or M MAX Area reduced but did not consistently remove the influence of MED which still explained up to 16% (M MAX P-P) and 23% (M MAX Area) of the variance. In conclusion, M MAX P-P was the better normalization parameter for removing the influence of electrode location and substantially reduced but did not consistently remove the influence of subcutaneous adiposity., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The effect of different strength training regimes, and in particular training utilizing brief explosive contractions, on tendinous tissue properties is poorly understood. This study compared the efficacy of 12 weeks of knee extensor explosive-contraction (ECT; n = 14) vs. sustained-contraction (SCT; n = 15) strength training vs. a non-training control ( n = 13) to induce changes in patellar tendon and knee extensor tendon-aponeurosis stiffness and size (patellar tendon, vastus-lateralis aponeurosis, quadriceps femoris muscle) in healthy young men. Training involved 40 isometric knee extension contractions (three times/week): gradually increasing to 75% of maximum voluntary torque (MVT) before holding for 3 s (SCT), or briefly contracting as fast as possible to ∼80% MVT (ECT). Changes in patellar tendon stiffness and Young's modulus, tendon-aponeurosis complex stiffness, as well as quadriceps femoris muscle volume, vastus-lateralis aponeurosis area and patellar tendon cross-sectional area were quantified with ultrasonography, dynamometry, and magnetic resonance imaging. ECT and SCT similarly increased patellar tendon stiffness (20% vs. 16%, both p < 0.05 vs. control) and Young's modulus (22% vs. 16%, both p < 0.05 vs. control). Tendon-aponeurosis complex high-force stiffness increased only after SCT (21%; p < 0.02), while ECT resulted in greater overall elongation of the tendon-aponeurosis complex. Quadriceps muscle volume only increased after sustained-contraction training (8%; p = 0.001), with unclear effects of strength training on aponeurosis area. The changes in patellar tendon cross-sectional area after strength training were not appreciably different to control. Our results suggest brief high force muscle contractions can induce increased free tendon stiffness, though SCT is needed to increase tendon-aponeurosis complex stiffness and muscle hypertrophy.

Aim: The potential for tendinous tissues to adapt to functional overload, especially after several years of exposure to heavy-resistance training, is largely unexplored. This study compared the morphological and mechanical characteristics of the patellar tendon and knee extensor tendon-aponeurosis complex between young men exposed to long-term (4 years; n = 16), short-term (12 weeks; n = 15) and no (untrained controls; n = 39) functional overload in the form of heavy-resistance training., Methods: Patellar tendon cross-sectional area, vastus lateralis aponeurosis area and quadriceps femoris volume, plus patellar tendon stiffness and Young's modulus, and tendon-aponeurosis complex stiffness, were quantified with MRI, dynamometry and ultrasonography., Results: As expected, long-term trained had greater muscle strength and volume (+58% and +56% vs untrained, both P < .001), as well as a greater aponeurosis area (+17% vs untrained, P < .01), but tendon cross-sectional area (mean and regional) was not different between groups. Only long-term trained had reduced patellar tendon elongation/strain over the whole force/stress range, whilst both short-term and long-term overload groups had similarly greater stiffness/Young's modulus at high force/stress (short-term +25/22%, and long-term +17/23% vs untrained; all P < .05). Tendon-aponeurosis complex stiffness was not different between groups (ANOVA, P = .149)., Conclusion: Despite large differences in muscle strength and size, years of resistance training did not induce tendon hypertrophy. Both short-term and long-term overload demonstrated similar increases in high-force mechanical and material stiffness, but reduced elongation/strain over the whole force/stress range occurred only after years of overload, indicating a force/strain specific time-course to these adaptations., (© 2017 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.)

Hamstrings muscle fiber composition may be predominantly fast-twitch and could explain the high incidence of hamstrings strain injuries. However, hamstrings muscle composition in vivo, and its influence on knee flexor muscle function, remains unknown. We investigated biceps femoris long head (BFlh) myosin heavy chain (MHC) composition from biopsy samples, and the association of hamstrings composition and hamstrings muscle volume (using MRI) with knee flexor maximal and explosive strength. Thirty-one young men performed maximal (concentric, eccentric, isometric) and explosive (isometric) contractions. BFlh exhibited a balanced MHC distribution [mean ± SD (min-max); 47.1 ± 9.1% (32.6-71.0%) MHC-I, 35.5 ± 8.5% (21.5-60.0%) MHC-IIA, 17.4 ± 9.1% (0.0-30.9%) MHC-IIX]. Muscle volume was correlated with knee flexor maximal strength at all velocities and contraction modes (r = 0.62-0.76, P < 0.01), but only associated with late phase explosive strength (time to 90 Nm; r = -0.53, P < 0.05). In contrast, BFlh muscle composition was not related to any maximal or explosive strength measure. BFlh MHC composition was not found to be "fast", and therefore composition does not appear to explain the high incidence of hamstrings strain injury. Hamstrings muscle volume explained 38-58% of the inter-individual differences in knee flexor maximum strength at a range of velocities and contraction modes, while BFlh muscle composition was not associated with maximal or explosive strength., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Purpose: Whilst neural and morphological adaptations following resistance training (RT) have been investigated extensively at a group level, relatively little is known about the contribution of specific physiological mechanisms, or pre-training strength, to the individual changes in strength following training. This study investigated the contribution of multiple underpinning neural [agonist EMG (QEMG MVT ), antagonist EMG (HEMG ANTAG )] and morphological variables [total quadriceps volume (QUADS VOL ), and muscle fascicle pennation angle (QUADSθ p )], as well as pre-training strength, to the individual changes in strength after 12 weeks of knee extensor RT., Methods: Twenty-eight healthy young men completed 12 weeks of isometric knee extensor RT (3/week). Isometric maximum voluntary torque (MVT) was assessed pre- and post-RT, as were simultaneous neural drive to the agonist (QEMG MVT ) and antagonist (HEMG ANTAG ). In addition QUADS VOL was determined with MRI and QUADSθ p with B-mode ultrasound., Results: Percentage changes (∆) in MVT were correlated to ∆QEMG MVT (r = 0.576, P = 0.001), ∆QUADS VOL (r = 0.461, P = 0.014), and pre-training MVT (r = -0.429, P = 0.023), but not ∆HEMG ANTAG (r = 0.298, P = 0.123) or ∆QUADSθ p (r = -0.207, P = 0.291). Multiple regression analysis revealed 59.9% of the total variance in ∆MVT after RT to be explained by ∆QEMG MVT (30.6%), ∆QUADS VOL (18.7%), and pre-training MVT (10.6%)., Conclusions: Changes in agonist neural drive, quadriceps muscle volume and pre-training strength combined to explain the majority of the variance in strength changes after knee extensor RT (~60%) and adaptations in agonist neural drive were the most important single predictor during this short-term intervention.

New Findings: What is the central question of this study? Do tendon and/or muscle-tendon unit stiffness influence rate of torque development? What is the main finding and its importance? In our experimental conditions, some measures of relative (to maximal voluntary torque and tissue length) muscle-tendon unit stiffness had small correlations with voluntary/evoked rate of torque development over matching torque increments. However, absolute and relative tendon stiffness were unrelated to voluntary and evoked rate of torque development. Therefore, the muscle aponeurosis but not free tendon influences the relative rate of torque development. Factors other than tissue stiffness more strongly determine the absolute rate of torque development. The influence of musculotendinous tissue stiffness on contractile rate of torque development (RTD) remains opaque. In this study, we examined the relationships between both patellar tendon (PT) and vastus lateralis muscle-tendon unit (MTU) stiffness and the voluntary and evoked knee-extension RTD. Fifty-two healthy untrained men completed duplicate laboratory sessions. Absolute and relative RTD were measured at 50 N m or 25% maximal voluntary torque (MVT) increments from onset and sequentially during explosive voluntary and evoked octet isometric contractions (supramaximal stimulation; eight pulses at 300 Hz). Isometric MVT was also assessed. Patellar tendon and MTU stiffness were derived from simultaneous force and ultrasound recordings of the PT and vastus lateralis aponeurosis during constant RTD ramp contractions. Absolute and relative (to MVT and resting tissue length) stiffness (k) was measured over identical torque increments as RTD. Pearson's correlations tested relationships between stiffness and RTD measurements over matching absolute/relative torque increments. Absolute and relative PT k were unrelated to equivalent voluntary/evoked (r = 0.020-0.255, P = 0.069-0.891). Absolute MTU k was unrelated to voluntary or evoked RTD (r ≤ 0.191, P ≥ 0.184), but some measures of relative MTU k were related to relative voluntary/evoked RTD (e.g. RTD for 25-50% MVT, r = 0.374/0.353, P = 0.007/0.014). In conclusion, relative MTU k explained a small proportion of the variance in relative voluntary and evoked RTD (both ≤19%), despite no association of absolute MTU k or absolute/relative PT k with equivalent RTD measures. Therefore, the muscle-aponeurosis component but not free tendon was associated with relative RTD, although it seems that an overriding influence of MVT negated any relationship of absolute MTU k and absolute RTD., (© 2017 The Authors. Experimental Physiology © 2017 The Physiological Society.)

Training specificity is considered important for strength training, although the functional and underpinning physiological adaptations to different types of training, including brief explosive contractions, are poorly understood. This study compared the effects of 12 wk of explosive-contraction (ECT, n = 13) vs. sustained-contraction (SCT, n = 16) strength training vs. control (n = 14) on the functional, neural, hypertrophic, and intrinsic contractile characteristics of healthy young men. Training involved 40 isometric knee extension repetitions (3 times/wk): contracting as fast and hard as possible for ∼1 s (ECT) or gradually increasing to 75% of maximum voluntary torque (MVT) before holding for 3 s (SCT). Torque and electromyography during maximum and explosive contractions, torque during evoked octet contractions, and total quadriceps muscle volume (QUADSVOL) were quantified pre and post training. MVT increased more after SCT than ECT [23 vs. 17%; effect size (ES) = 0.69], with similar increases in neural drive, but greater QUADSVOL changes after SCT (8.1 vs. 2.6%; ES = 0.74). ECT improved explosive torque at all time points (17-34%; 0.54 ≤ ES ≤ 0.76) because of increased neural drive (17-28%), whereas only late-phase explosive torque (150 ms, 12%; ES = 1.48) and corresponding neural drive (18%) increased after SCT. Changes in evoked torque indicated slowing of the contractile properties of the muscle-tendon unit after both training interventions. These results showed training-specific functional changes that appeared to be due to distinct neural and hypertrophic adaptations. ECT produced a wider range of functional adaptations than SCT, and given the lesser demands of ECT, this type of training provides a highly efficient means of increasing function., (Copyright © 2016 the American Physiological Society.)

Purpose: This study examined the association of muscle size and strength for the quadriceps and hamstrings, the relationship between the size of these muscles, and whether the H:Q size ratio influenced reciprocal strength balance-widely regarded as a risk factor for hamstrings injury., Methods: Knee extensor and flexor isometric, concentric and eccentric (50 and 350° s(-1)) strength were measured in 31 healthy, recreationally active young men. Muscle volume was measured with magnetic resonance imaging., Results: The knee flexors achieved higher concentric and eccentric torques (normalised to isometric values) than the extensors. Muscle volume explained a significant part of the inter-individual differences in strength in both extensors (isometric 71%, concentric 30-31%) and flexors (isometric 38%, concentric 50-55%). Notably, muscle size was related to knee flexor eccentric strength (r = 0.69-0.76; R (2) = 48-58%) but not extensor eccentric strength. Quadriceps and hamstrings volumes were moderately correlated (r = 0.64), with the majority of the variance in the size of one muscle (59%) not explained by the size of the other muscle. The hamstrings-to-quadriceps (H:Q) volume ratio was correlated with the isometric (r = 0.45) and functional strength ratios (350° s(-1), r = 0.56; 50° s(-1), r = 0.34)., Conclusions: Muscle size exhibited a differential influence on knee extensor and flexor eccentric strength. Quadriceps and hamstrings muscle size was related, and the H:Q size ratio contributed to their strength ratios. Muscle size imbalances contribute to functional imbalances and these findings support the use of hamstrings strength training with an emphasis on hypertrophic adaptations for reducing injury risk.

Purpose: A disproportionately small biceps femoris long head (BFlh) proximal aponeurosis has been suggested as a risk factor for hamstring strain injury by concentrating mechanical strain on the surrounding muscle tissue. However, the size of the BFlh aponeurosis relative to BFlh muscle size, or overall knee flexor strength, has not been investigated. This study aimed to examine the relationship of BFlh proximal aponeurosis area with muscle size (maximal anatomical cross-sectional area (ACSAmax)) and knee flexor strength (isometric and eccentric)., Methods: Magnetic resonance images of the dominant thigh of 30 healthy young males were analyzed to measure BFlh proximal aponeurosis area and muscle ACSAmax. Participants performed maximum voluntary contractions to assess knee flexion maximal isometric and eccentric torque (at 50° s and 350° s)., Results: BFlh proximal aponeurosis area varied considerably between participants (more than fourfold, range = 7.5-33.5 cm, mean = 20.4 ± 5.4 cm, coefficient of variation = 26.6%) and was not related to BFlh ACSAmax (r = 0.04, P = 0.83). Consequently, the aponeurosis/muscle area ratio (defined as BFlh proximal aponeurosis area divided by BFlh ACSAmax) exhibited sixfold variability, being 83% smaller in one individual than another (0.53 to 3.09, coefficient of variation = 32.5%). Moreover, aponeurosis size was not related to isometric (r = 0.28, P = 0.13) or eccentric knee flexion strength (r = 0.24, P ≥ 0.20)., Conclusion: BFlh proximal aponeurosis size exhibits high variability between healthy young men, and it was not related to BFlh muscle size or knee flexor strength. Individuals with a relatively small aponeurosis may be at increased risk of hamstring strain injury.