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Determining how the quadriceps femoris musculotendinous unit functions, according to hip and knee joint angles, may help with clinical decisions when prescribing knee extension exercises. We aimed to determine the effect of hip and knee joint angles on structure and neuromuscular functioning of all constituents of the quadriceps femoris and patellar tendon properties. Twenty young males were evaluated in four positions: seated and supine in both 20° and 60° of knee flexion (SIT20, SIT60, SUP20, and SUP60). Peak knee extension torque was determined during maximal voluntary isometric contraction (MVIC). Ultrasound imaging was used at rest and during MVIC to characterize quadriceps femoris muscle and tendon aponeurosis complex stiffness. We found that peak torque and neuromuscular efficiency were higher for SUP60 and SIT60 compared to SUP20 and SIT20 position. We found higher fascicle length and lower pennation angle in positions with the knee flexed at 60°. The tendon aponeurosis complex stiffness, tendon force, stiffness, stress, and Young's modulus seemed greater in more elongated positions (60°) than in shortened positions (20°). In conclusion, clinicians should consider positioning at 60° of knee flexion rather than 20°, regardless if seated or supine, during rehabilitation to load the musculotendinous unit enough to stimulate a cellular response.

Assuntos

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BACKGROUND: Subtalar hyperpronation and ankle dorsiflexion restriction have been theoretically associated with Achilles tendinopathy (AT). However, evidence to support these associations is lacking. OBJECTIVES: To compare foot alignment and ankle dorsiflexion range of motion (ROM) between the symptomatic and non-symptomatic limbs of individuals with unilateral AT. And to verify whether differences exist between individuals with symptomatic pronated feet and individuals with symptomatic neutral/supinated feet in terms of tendon pain, structure, and symptom severity. METHODS: Sixty-three participants with unilateral AT underwent a bilateral evaluation of pain during tendon palpation, symptom severity, tendon thickening, tendon neovascularization, ankle dorsiflexion ROM, and foot posture alignment [foot posture index (FPI), navicular drop, navicular drift, and longitudinal arch angle (LAA)]. Side and group comparisons were made using t-tests and correlations were evaluated using the Pearson test. RESULTS: There were no differences between the symptomatic and non-symptomatic limbs regarding foot posture alignment. Specifically, non-significant negligible differences were observed between limbs regarding FPI [mean difference (MD)=-0.23; 95% confidence interval (CI)=-0.70, 0.25), navicular drop (MD=0.58 mm; 95%CI=-0.25, 1.43), navicular drift (MD=0.16 mm; 95%CI=-0.77, 1.09), and LAA (MD=0.30º; 95%CI=-1.74, 2.34). There was no difference between limbs regarding ankle dorsiflexion ROM. However, lower ankle dorsiflexion was associated with worse symptom severity (r = 0.223). Finally, no difference was observed between individuals with symptomatic pronated feet and individuals with symptomatic neutral/supinated feet in terms of tendon pain or structure. CONCLUSIONS: Static foot alignment measures do not seem to be clinically relevant in patients with AT. Smaller ankle dorsiflexion ROM, however, was associated with greater symptom severity in this population.

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Muscle-tendon unit length plays a crucial role in quadriceps femoris muscle (QF) physiological adaptation, but the influence of hip and knee angles during QF neuromuscular electrical stimulation (NMES) is poorly investigated. We investigated the effect of muscle length on maximum electrically induced contraction (MEIC) and current efficiency. We secondarily assessed the architecture of all QF constituents and their tendon-aponeurosis complex (TAC) displacement to calculate a stiffness index. This study was a randomized, repeated measure, blinded design with a sample of twenty healthy men aged 24.0 ± 4.6. The MEIC was assessed in four different positions: supine with knee flexion of 60° (SUP60); seated with knee flexion of 60° (SIT60); supine with knee flexion of 20° (SUP20), and seated with knee flexion of 20° (SIT20). The current efficiency (MEIC/maximum tolerated current amplitude) was calculated. Ultrasonography of the QF was performed at rest and during NMES to measure pennation angle (θ p ) and fascicle length (L f ), and the TAC stiffness index. MEIC and current efficiency were greater for SUP60 and SIT60 compared to SUP20 and SIT20. The vastus lateralis and medialis showed lower θ p and higher L f at SUP60 and SIT60, while for the rectus femoris, in SUP60 there were lower θ p and higher L f than in all positions. The vastus intermedius had a similar pattern to the other vastii, except for lack of difference in θ p between SIT60 compared to SUP20 and SIT20. The TAC stiffness index was greater for SUP60. We concluded that NMES generate greater torque and current efficiency at 60° of knee flexion, compared to 20°. For these knee angles, lengthening the QF at the hip did not promote significant change. Each QF constituent demonstrated muscle physiology patterns according to hip and/or knee angles, even though a greater L f and lower θ p were predominant in SUP60 and SIT60. QF TAC index stiffened in more elongated positions, which probably contributed to enhanced force transmission and slightly higher torque in SUP60. Our findings may help exercise physiologist better understand the impact of hip and knee angles on designing more rational NMES stimulation strategies. CLINICAL TRIAL REGISTRATION: www.ClinicalTrials.gov, identifier NCT03822221.

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PURPOSE: The purposes of our study were to evaluate Achilles tendon loading profiles of various exercises and to develop guidelines to incrementally increase the rate and magnitude of Achilles tendon loading during rehabilitation. METHODS: Eight healthy young adults completed a battery of rehabilitation exercises. During each exercise, we collected three-dimensional motion capture and ground reaction force data to estimate Achilles tendon loading biomechanics. Using these loading estimates, we developed an exercise progression that incrementally increases Achilles tendon loading based on the magnitude, duration, and rate of tendon loading. RESULTS: We found that Achilles tendon loading could be incrementally increased using a set of either isolated ankle movements or multijoint movements. Peak Achilles tendon loads varied more than 12-fold, from 0.5 bodyweights during a seated heel raise to 7.3 bodyweights during a forward single-leg hop. Asymmetric stepping movements like lunges, step ups, and step downs provide additional flexibility for prescribing tendon loading on a side-specific manner. CONCLUSION: By establishing progressions for Achilles tendon loading, rehabilitative care can be tailored to address the specific needs of each patient. Our comprehensive data set also provides clinicians and researchers guidelines on how to alter magnitude, duration, and rate of loading to design new exercises and exercise progressions based on the clinical need.

Assuntos