Change of direction speed (CODS) is often considered a main determinant of successful performance in many team sports and is routinely measured using field-based tests. However, controversy regarding test selection still exists based upon the reliability and specificity of the tests. The purpose of this study was to determine and compare the reliability, factorial validity, and interrelationships of five frequently used CODS tests (Illinois, L-Run, Pro-Agility, T-test, and 505). Forty-four physical education students (male n = 24; female n = 20; age; 16.7 ± 0.6), who compete within team sports, to varying levels of competition, participated in this study. Three trials for each of the five tests were recorded. All tests had high (intraclass correlation coefficient) test-retest reliability (r = 0.88-0.95) and low typical percentage error (1.95-2.40%). The principle component factor analysis resulted in the extraction of one significant component which explained 89.52% of the total variance. All selected tests were positively and strongly correlated (r = 0.84-0.89). Based upon the results of this study, it was concluded that all tests are highly reliable and valid measures of CODS, with all tests assessing a general athletic ability to change direction. Future research should investigate the factorial validity of the CODS test within homogenous samples.

Blazevich AJ, Cannavan D, Waugh CM, Miller SC, Thorlund JB, Aagaard P, Kay AD. Range of motion, neuromechanical, and architectural adaptations to plantar flexor stretch training in humans. 117: 452-462, 2014. First published June 19, 2014 doi:10.1152/japplphysiol.00204.2014.-The neuromuscular adaptations in response to muscle stretch training have not been clearly described. In the present study, changes in muscle (at fascicular and whole muscle levels) and tendon mechanics, muscle activity, and spinal motoneuron excitability were examined during standardized plantar flexor stretches after 3 wk of twice daily stretch training (4 ϫ 30 s). No changes were observed in a nonexercising control group (n ϭ 9), however stretch training elicited a 19.9% increase in dorsiflexion range of motion (ROM) and a 28% increase in passive joint moment at end ROM (n ϭ 12). Only a trend toward a decrease in passive plantar flexor moment during stretch (Ϫ9.9%; P ϭ 0.15) was observed, and no changes in electromyographic amplitudes during ROM or at end ROM were detected. Decreases in H max:Mmax (tibial nerve stimulation) were observed at plantar flexed (gastrocnemius medialis and soleus) and neutral (soleus only) joint angles, but not with the ankle dorsiflexed. Muscle and fascicle strain increased (12 vs. 23%) along with a decrease in muscle stiffness (Ϫ18%) during stretch to a constant target joint angle. Muscle length at end ROM increased (13%) without a change in fascicle length, fascicle rotation, tendon elongation, or tendon stiffness following training. A lack of change in maximum voluntary contraction moment and rate of force development at any joint angle was taken to indicate a lack of change in series compliance of the muscle-tendon unit. Thus, increases in end ROM were underpinned by increases in maximum tolerable passive joint moment (stretch tolerance) and both muscle and fascicle elongation rather than changes in volitional muscle activation or motoneuron pool excitability. J Appl Physiol

Accurate and reliable estimation of muscle moment arms is a prerequisite for the development of musculoskeletal models. Numerous techniques are available to estimate the Achilles tendon moment arm in vivo. The purposes of this study were 1) to compare in vivo Achilles tendon moment arms obtained using the center of rotation (COR) and tendon excursion (TE) methods and 2) to assess the reliability of each method. For the COR method, magnetic resonance (MR) images from nine participants were obtained at ankle angles of −15°, 0°, and +15° and analyzed using Reuleaux' method. For the TE method, the movement of the gastrocnemius medialis-Achilles tendon junction was recorded using ultrasonography as the ankle was passively rotated through its range of motion. The Achilles tendon moment arm was obtained by differentiation of tendon displacement with respect to ankle angular excursion using seven different differentiation techniques. Moment arms obtained using the COR method were significantly greater than those obtained using the TE method ( P < 0.01), but results from both methods were well correlated. The coefficient of determination between moment arms derived from the COR and TE methods was highest when tendon displacement was linearly differentiated over a ±10° interval ( R2 = 0.94). The between-measurement coefficient of variation was 3.9% for the COR method and 4.5–9.7% for the TE method, depending on the differentiation technique. The high reliabilities and strong relationship between methods demonstrate that both methods are robust against their limitations. The large absolute between-method differences (∼25–30%) in moment arms have significant implications for their use in musculoskeletal models.

Friction drilling is a nontraditional hole-making process. A rotating conical tool is applied to penetrate a hole and create a bushing in a single step without generating chips. Friction drilling relies on the heat generated from the frictional force between the tool and sheet metal workpiece to soften, penetrate, and deform the work-material into a bushing shape. The mechanical and thermal aspects of friction drilling are studied in this research. Under the constant tool feed rate, the experimentally measured thrust force and torque were analyzed. An infrared camera is applied to measure the temperature of the tool and workpiece. Two models are developed for friction drilling. One is the thermal finite element model to predict the distance of tool travel before the workpiece reaches the 250°C threshold temperature that is detectable by an infrared camera. Another is a force model to predict the thrust force and torque in friction drilling based on the measured temperature, material properties, and estimated area of contact. The results of this study are used to identify research needs and build the foundation for future friction drilling process optimization.

Maximum joint range of motion is an important parameter influencing functional performance and musculoskeletal injury risk. Nonetheless, a complete description of the muscle architectural and tendon changes that occur during stretch and the factors influencing maximum range of motion is lacking. We measured muscle-tendon elongation and fascicle lengthening and rotation sonographically during maximal plantar flexor stretches in 21 healthy men. Electromyogram (EMG) recordings were obtained synchronously with ultrasound and joint moment data, and H-reflex measurements were made with the ankle at neutral (0°) and dorsiflexed (50% maximal passive joint moment) positions; the maximum H amplitude (normalized to maximum M-wave amplitude; M(max)) and H-amplitude elicited at a stimulation intensity that evoked 10% M(max) were obtained. Maximal stretch was accomplished through significant muscle (14.9%; 30 mm) and tendon lengthening (8.4%; 22 mm). There were similar relative changes in fascicle length and angle, but planimetric modeling indicated that the contribution of fascicle rotation to muscle lengthening was small (<4 mm). Subjects with a greater range of motion showed less resistance to stretch and a greater passive joint moment at stretch termination than less flexible subjects (i.e., greater stretch tolerance). Also, greater fascicle rotation accompanied muscle elongation (9.7 vs. 5.9%) and there was a greater tendon length at stretch termination in more flexible subjects. Finally, a moderate correlation between the angle of EMG onset and maximum range of motion was obtained (r = 0.60, P < 0.05), despite there being no difference in H-reflex magnitudes between the groups. Thus clear differences in the neuromuscular responses to stretch were observed between "flexible" and "inflexible" subjects.

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Background Neuromuscular deficits are common following knee injuries and may contribute to early-onset post-traumatic osteoarthritis, likely mediated through quadriceps dysfunction. Objective To identify how peri-articular neuromuscular function changes over time after knee injury and surgery. Design Systematic review with meta-analyses. Data Sources PubMed, Web of Science, Embase, Scopus, CENTRAL (Trials). Eligibility Criteria for Selecting Studies Moderate and high-quality studies comparing neuromuscular function of muscles crossing the knee joint between a knee-injured population (ligamentous, meniscal, osteochondral lesions) and healthy controls. Outcomes included normalized isokinetic strength, muscle size, voluntary activation, cortical and spinal-reflex excitability, and other torque related outcomes. Results A total of 46 studies of anterior cruciate ligament (ACL) and five of meniscal injury were included. For ACL injury, strength and voluntary activation deficits were evident (moderate to strong evidence). Cortical excitability was not affected at < 6 months (moderate evidence) but decreased at 24+ months (moderate evidence). Spinal-reflex excitability did not change at < 6 months (moderate evidence) but increased at 24+ months (strong evidence). We also found deficits in torque variability, rate of torque development, and electromechanical delay (very limited to moderate evidence). For meniscus injury, strength deficits were evident only in the short-term. No studies reported gastrocnemius, soleus or popliteus muscle outcomes for either injury. No studies were found for other ligamentous or chondral injuries. Conclusions Neuromuscular deficits persist for years post-injury/surgery, though the majority of evidence is from ACL injured populations. Muscle strength deficits are accompanied by neural alterations and changes in control and timing of muscle force, but more studies are needed to fill the evidence gaps we have identified. Better characterisation and therapeutic strategies addressing these deficits could improve rehabilitation outcomes, and potentially prevent PTOA. Trial Registration Number PROSPERO CRD42019141850.

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