Andrea Monte

We combined ultrasound, EMG and dynamometry measurements to establish differences in neuromechanical adaptations following two resistance training programs of equal training volume, one involving a multi-joint exercise and the second a single-joint exercise. Twenty-four participants were divided into a squat group (SQG) and a leg extension group (LEG). Both groups performed ten weeks of training. Before and after the training protocol, muscle architecture of the knee extensors was quantified in vivo using an ultrasound apparatus. The vastus lateralis (VL) torque-fascicle length relationship was also obtained. The maximum isometric torque (Tmax), the maximum EMG activity and the optimal VL fascicle length (L ₀ ) were determined. A significant increase in 1RM ( P < 0.001) was observed in both groups post-training. Muscle thickness increased in both groups ( P = 0.008 and P < 0.001 LEG and SQG, respectively), but the increase was greater in SQG than LEG ( P = 0.031). Both groups showed significant changes in Tmax ( P = 0.0084 and P = 0.0044 for LEG and SQG, respectively) and the improvement in T _max was larger ( P = 0.041) for SQG (+ 14%) than LEG (+ 10%). Pennation angle, fascicle length and VL L ₀ increased post-training in SQG only. A transfer effect of 1RM was observed in both groups: SQG improved the leg extension 1RM by about 16%, whereas LEG increased the squat 1RM by about 9%; SQG showed a larger strength improvement transfer than LEG ( P = 0.037). Due to the high knee torque required to maintain a given external load, squat exercise training may be more effective than the leg-extension setup used in the present study in eliciting neuromuscular adaptations.

The physiological determinants of explosive strength are usually investigated separately. We aimed to quantify the relative contributions of muscle excitation, structural, and mechanical determinants of rapid torque production in the knee extensors in a multi‐domain framework. Twenty‐four young adults performed ballistic isometric knee extensions. High‐density surface electromyographic (HD‐sEMG) signals were recorded from vasti lateralis and medialis muscles. Patellar tendon stiffness and muscle architecture were assessed via ultrasound. Impulse and RTD _peak were outcomes. The predictors were from four domains: muscle excitation, muscle thickness, fascicle shortening velocity, and tendon stiffness. Linear regressions and LMG were used to quantify the weight of each predictor. The models explained substantial variance in impulse: R ² = 0.62 (0–50 ms), 0.76 (0–75 ms), 0.74 (0–100 ms), 0.61 (0–125 ms), 0.70 (0–150 ms). Early impulse (50 and 75 ms) was mainly explained by tendon stiffness and muscle excitation; mid‐phase impulse (100 ms) by fascicle velocity and tendon stiffness; late impulse (125 and 150 ms) by fascicle shortening velocity and muscle thickness. RTD _peak was explained (R ² = 0.70) by patellar tendon stiffness (~32% of impulse variance), fascicle velocity (~18%), muscle thickness (~12%), and muscle excitation (~8%). Four predictors across different neuromechanical domains explained up to 76% of the variance in rapid torque production. Interestingly, the determinants shift over time: tendon stiffness and muscle excitation dominate earlier, while fascicle dynamics and muscle size become more important later. RTD _peak was largely determined by tendon stiffness and a balanced contribution of muscular predictors.

Aims: This study aimed to investigate the impact of type 2 diabetes (T2D) on muscle and tendon mechanics by comparing individuals with controlled diabetes to a healthy cohort matched for age, BMI, and physical activity level. A secondary aim was to investigate the possible association between muscle-tendon proprieties and glycated haemoglobin (HbA1c) or advanced glycated end products (AGE, RAGE) as determined in blood and skin biopsies. Methods: Twenty-eight patients and eighteen controls were recruited for this study. Achilles tendon stiffness (k _T ), muscle-tendon stiffness (k _M , in gastrocnemius medialis) and the rate of torque development (RTD) were evaluated by combining dynamometric and ultrasound data. Results: Diabetic patients showed increased tendon stiffness and reduced tendon elongation compared to controls, but similar RTD and k _M values. No differences in advanced glycation end products (in serum or biopsies) were observed between cohorts, but a significant positive correlation was observed between k _T and HbA1c ( r = 0.610, N = 46, P < 0.001). Conclusion: Our data indicate that muscle, but not tendon, properties can be preserved in controlled and physically active diabetic patients and that higher tendon stiffness does not result in a functional deficit (i.e., same explosive capacity between cohorts). Although this study is cross-sectional and has a limited sample size, our data suggest a potential role of HbA1c as a non-invasive biomarker of altered tendon mechanics in people with diabetes. ClinicalTrials.gov, protocol number: NCT05585502.

Skeletal muscle is heterogeneous in its architecture, with regional differences in fiber length and pennation angle that make up anatomically distinct regions. This study aimed to understand how these regional differences influence vastus lateralis (VL) behavior during isokinetic contractions in vivo. Knee extensor torque was measured in twelve healthy young adults using an isokinetic dynamometer during maximal contractions at different angular velocities (30° s⁻¹, 75° s⁻¹, 150° s⁻¹, 210° s⁻¹, 270° s⁻¹). The fascicle length of VL was recorded by two ultrasound devices in its distal and middle regions, and muscle‐belly length was calculated as the longitudinal length change in the muscle belly. Fascicle (Vf) and muscle‐belly (Vm) velocities were calculated as the first derivative of the length–time curve in the phase at constant angular velocity. Muscle‐belly gearing (Gb) was calculated as Vm/Vf. At rest, greater thickness and pennation angles and lower fascicle lengths were observed in the middle vs. distal regions. During contraction, Vf and Vm increased as a function of angular velocity in both the investigated regions. The distal regions showed higher Vf and Vm values at all the investigated angular velocities. Significant differences in Gb were observed between regions but not as a function of knee angular velocity. Our data indicate that the architectural differences within a muscle affect the behavior of the active components during contraction. These results could help develop new musculoskeletal models to predict the muscle's mechanical output better.

In an asymptomatic population, we investigated the relationships between glycated haemoglobin (HbA1c) and cartilage T2 relaxation time at the knee joint level. Fourteen and 17 participants with high and normal levels of HbA1c were recruited, respectively. A blood sample was used to determine the HbA1c level. T2 relaxation time (T2) of the superficial and deep parts of the femoral cartilage in the anterior, central, and posterior topographical sites was calculated using magnetic resonance (1.5 T) images. Each participant completed a knee injury and osteoarthritis outcome score questionnaire (KOOS) and a series of biomechanical analyses while running at their self-selected speed. The group with a high level of HbA1c had a lower score of KOOS symptoms than the other group (P < 0.05). HbA1c was found to be negatively related to the KOOS symptoms score. The group with a high level of HbA1c had low T2 values in all of the investigated topographical sites of the knee femoral cartilage (P < 0.05 in all cases). T2 was negatively correlated with HbA1c levels in all investigated knee femoral cartilage regions. Our data suggest that the subjects with high levels of HbA1c were those with low knee joint symptoms and lower values of T2. These results indicate that HbA1c could be correlated with cartilage deterioration due to its ability to dehydrate collagen fibre, possibly acting as a risk factor for the development of osteoarthritis.

In this study, we investigated the capability of the Nakagami transformation to detect changes in vastus lateralis muscle-tendon stiffness (k) during dynamic (and intense) contractions. k was evaluated in eleven healthy males using the gold-standard method (a combination of ultrasound and dynamometric measurements) during maximal and sub-maximal voluntary fixed-end contractions of the knee extensors (20, 40, 60, 80, and 100% of maximum voluntary force), while Nakagami parameters were analysed using the Nakagami transformation during the same contractions. Muscle-belly behaviour was investigated by means of B-mode ultrasound analysis, while Nakagami parameters were obtained in post-processing using radiofrequency data. k was calculated as the slope of the force-muscle-belly elongation relationship. Three contractions at each intensity were performed to calculate the intra-trial reliability and the coefficient of variation (CV) of the Nakagami parameters. At all contraction intensities, high values of intra-trial reliability (range: 0.92–0.96) and low CV (k and Nakagami parameters increased as a function of contraction intensity, and significant positive correlations were observed between these variables. These data suggest that changes in mechanical properties (e.g., stiffness) at the muscle level could be investigated by means of Nakagami parameters.