Stefano Longo

Training-induced changes in structural and mechanical properties of the patellar tendon are related to muscle hypertrophy but not to strength gains

To obtain a better understanding of the adaptations of human tendon to chronic overloading, we examined the relationships between these adaptations and the changes in muscle structure and function. Fifteen healthy male subjects (20+/-2 yr) underwent 9 wk of knee extension resistance training. Patellar tendon stiffness and modulus were assessed with ultrasonography, and cross-sectional area (CSA) was determined along the entire length of the tendon by using magnetic resonance imaging. In the quadriceps muscles, architecture and volume measurements were combined to obtain physiological CSA (PCSA), and maximal isometric force was recorded. Following training, muscle force and PCSA increased by 31% (P<0.0001) and 7% (P<0.01), respectively. Tendon CSA increased regionally at 20-30%, 60%, and 90-100% of tendon length (5-6%; P<0.05), and tendon stiffness and modulus increased by 24% (P<0.001) and 20% (P<0.01), respectively. Although none of the tendon adaptations were related to strength gains, we observed a positive correlation between the increase in quadriceps PCSA and the increases in tendon stiffness (r=0.68; P<0.01) and modulus (r=0.75; P<0.01). Unexpectedly, the increase in muscle PCSA was inversely related to the distal and the mean increases in tendon CSA (in both cases, r=-0.64; P<0.05). These data suggest that, following short-term resistance training, changes in tendon mechanical and material properties are more closely related to the overall loading history and that tendon hypertrophy is driven by other mechanisms than those eliciting tendon stiffening.

Differential adaptations to eccentric versus conventional resistance training in older humans

We hypothesized that training with eccentric contractions only (therefore using higher loads) would yield greater muscle structural and strength gains compared with conventional resistance training. Nine older adults (mean ±s.d. age, 74 ± 3 years) were assigned to a conventional (CONV) resistance training group performing both concentric and eccentric contractions and 10 (age, 67 ± 2 years) to an eccentric‐only (ECC) resistance training group. Both groups trained three times per week for 14 weeks at 80% of the five‐repetition maximum, specific to each training mode. Maximal knee extensor torque was assessed during isometric, concentric and eccentric contractions across a range of angular velocities (0–3.49 rad s−1). Vastus lateralis muscle architecture (fascicle length, pennation angle and muscle thickness) was assessed in vivo at rest using ultrasonography. Training increased fascicle length in both groups, but the increase was significantly greater in the ECC (20% increase) than the CONV group (8% increase). Conversely, pennation angle significantly increased in the CONV (35% increase) but not in the ECC group (5% increase). Muscle thickness increased to a similar extent in both groups (∼12% increase). In the ECC group, eccentric knee extensor torque increased by 9–17% across velocities, but concentric torque was unchanged. Conversely, in the CONV group, concentric torque increased by 22–37% across velocities, but eccentric torque was unchanged. Instead, isometric torque increased to a similar extent in both groups (∼8% increase). Thus, the two training regimens resulted in differential adaptations in muscle architecture and strength. These results suggest that the stimulus for adding sarcomeres in‐series and in‐parallel may be different, which implies that different myogenic responses were induced by the two different training methods.

Human muscle fascicle behavior in agonist and antagonist isometric contractions

Introduction: The aim of this study was to compare, at a given level of electromyographic (EMG) activity, the behavior of dorsiflexor and plantarflexor muscles as assessed via their architecture (pennation angle and fiber length) during agonist or antagonist isometric contractions. Methods: Real‐time ultrasonography and EMG activity of gastrocnemius medialis (GM) and tibialis anterior (TA) muscles were obtained while young males performed ramp isometric contractions in dorsi‐ and plantarflexion. Results: For both muscles, at a similar level of EMG activity, fiber length was longer, and pennation angle was smaller, during antagonist than during agonist contractions. Conclusions: These results indicate that, at similar levels of EMG activity, GM and TA muscles elicit a higher mechanical output while acting as an antagonist. These findings have important implications for muscle function testing. They show that estimation of antagonistic force using the common method based on the EMG/net torque relationship yields underestimated values. Muscle Nerve 45: 92–99, 2012

Stretch-induced changes in tension generation process and stiffness are not accompanied by alterations in muscle architecture of the middle and distal portions of the two gastrocnemii

The study aimed to evaluate the stretch-induced changes in muscle architecture in different portions of the gastrocnemius medialis (GM) and lateralis (GL) muscles. The reliability and sensitivity of the measurements were also assessed. Fascicle length (FL) and pennation angle (PA) were calculated in the middle and distal portions of GM and GL at 0°, 10° and 20° of ankle dorsiflexion. At the same angles, passive torque (Tpass), peak torque (pT) and myotendinous junction displacement of GM were determined. Stiffness was calculated at muscle-tendon unit (MTU), muscle and tendon level. After static stretching administration, Tpass, pT and MTU stiffness decreased by 22%, 12% and 16%, respectively (p<0.05). Muscle and tendon stiffness decreased by 15% and 16% (p<0.05). Nevertheless, no changes in FL and PA occurred. The reliability of the approach was always very high (intraclass correlation coefficient>0.90), with an adequate level of sensitivity. pT after static stretching was related to decreases in MTU, muscle and tendon stiffness, but not to alterations in muscle architecture.

Muscle thickness correlates to muscle cross-sectional area in the assessment of strength training-induced hypertrophy

Muscle thickness (MT) measured by ultrasound has been used to estimate cross‐sectional area (measured by CT and MRI) at a single time point. We tested whether MT could be used as a valid marker of MRI determined muscle anatomical cross‐sectional area (ACSA) and volume changes following resistance training (RT). Nine healthy, young, male volunteers (24 ± 2 y.o., BMI 24.1 ± 2.8 kg/m2) had vastus lateralis (VL) muscle volume (VOL) and ACSAmid (at 50% of femur length, FL) assessed by MRI, and VL MT measured by ultrasound at 50% FL. Measurements were taken at baseline and after 12 weeks of isokinetic RT. Differences between baseline and post‐training were assessed by Students paired t test. The relationships between MRI and ultrasound measurements were tested by Pearsons correlation. After RT, MT increased by 7.5 ± 6.1% (P < .001), ACSAmid by 5.2 ± 5% (P < .001), and VOL by 5.0 ± 6.9% (P < .05) (values: means ± SD). Positive correlations were found, at baseline and 12 weeks, between MT and ACSAmid (r = .82, P < .001 and r = .73, P < .001, respectively), and between MT and VOL (r = .76, P < .001 and r = .73, P < .001, respectively). The % change in MT with training was correlated with % change in ACSAmid (r = .69, P < .01), but not % change in VOL (r = .33, P > .05). These data support evidence that MT is a reliable index of muscle ACSAmid and VOL at a single time point. MT changes following RT are associated with parallel changes in muscle ACSAmid but not with the changes in VOL, highlighting the impact of RT on regional hypertrophy.

Mechanomyogram amplitude correlates with human gastrocnemius medialis muscle and tendon stiffness both before and after acute passive stretching

What is the central question of this study? The aim of this study was to determine the possible correlations between the mechanomyogram signal amplitude and the stiffness at the muscle–tendon unit, muscle and tendon levels, which were only hypothesised in previous investigations. What is the main finding and its importance? The main findings of this study are that the amplitude of the mechanomyogram was correlated inversely, albeit with small r2 values, with muscle–tendon unit, muscle and tendon stiffness both before and after application of stretching.

Imaging of shoulder pain in overhead throwing athletes

Overhead sports are widely practiced around the world and overhead athletes can present with pain and dysfunction in the throwing shoulder, generally due to degenerative changes secondary to overuse. Numerous etiologies can be taken into account, including rotator cuff and glenoid labrum tears, biceps pathologies, internal impingement, and gleno-humeral instability. In this setting, imaging plays a central role in early diagnosis, thus allowing for a prompt management, correct rehabilitation, and quick return to competition. This review is aimed to discuss the role of imaging to diagnose the most common types of overhead-related shoulder injuries.

Correlations between upper limb oxygen kinetics and performance in elite swimmers

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INTERPRETATION AND PERCEPTION OF TWO DIFFERENT KUMITE FIGHTING INTENSITIES THROUGH AN INTEGRATED APPROACH TRAINING IN INTERNATIONAL LEVEL KARATEKAS: AN EXPLORATORY STUDY.

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