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Context: Assessments of skeletal-muscle functional capacity often necessitate maximal contractile effort, which exacerbates muscle fatigue or injury. Tensiomyography (TMG) has been investigated as a means to assess muscle contractile function after fatigue; however, observations have not been contextualized by concurrent physiological measures. Objective: To measure peripheral-fatigue-induced alterations in mechanical and contractile properties of the plantar-flexor muscles through noninvasive TMG concurrently with maximal voluntary contraction (MVC) and passive muscle tension (PMT) to validate TMG as a gauge of peripheral fatigue. Design: Pre- and posttest intervention with control. Setting: University laboratory. Participants: 21 healthy male volunteers. Interventions: Subjects' plantar flexors were tested for TMG parameters, along with MVC and PMT, before and after either a 5-min rest period (control) or a 5-min electrical-stimulation intervention (fatigue). Main Outcome Measures: Temporal (contraction velocity) and spatial (radial displacement) contractile parameters of the gastrocnemius medialis were recorded through TMG. MVC was measured as an indicator of muscle fatigue, and PMT was measured to assess muscle stiffness. Results: Radial displacement demonstrated a fatigue-associated reduction (3.3 ± 1.2 vs 4.0 ± 1.4 mm, P = .031), while contraction velocity remained unaltered. In addition, MVC significantly declined by 122.6 ± 104 N (P < .001) after stimulation (fatigue). PMT was significantly increased after fatigue (139.8 ± 54.3 vs 111.3 ± 44.6 N, P = .007). Conclusions: TMG successfully detected fatigue, evident from reduced MVC, by displaying impaired muscle displacement accompanied by elevated PMT. TMG could be useful in establishing skeletalmuscle fatigue status without exacerbating the functional decrement of the muscle. [ABSTRACT FROM AUTHOR]

Background: The plantaris tendon (PT) has been thought to contribute to symptoms in a proportion of patients with Achilles midportion tendinopathy, with symptoms improving after PT excision. Hypothesis: There is compression and differential movement between the PT and Achilles tendon (AT) during ankle plantarflexion and dorsiflexion. Study Design: Descriptive laboratory study. Methods: Eighteen fresh-frozen cadaveric ankles (mean ± SD age: 35 ± 7 years, range = 27-48 years; men, n = 9) were mounted in a customized testing rig, where the tibia was fixed but the forefoot could be moved freely. A Steinmann pin was drilled through the calcaneus, enabling a valgus torque to be applied. The soleus, gastrocnemius, and plantaris muscles were loaded with 63 N with a weighted pulley system. The test area was 40 to 80 mm above the os calcis, corresponding to where the injury is observed clinically. Medially, the AT and PT were exposed, and a calibrated flexible pressure sensor was inserted between the tendons. Pressure readings were recorded with the ankle in full dorsiflexion, full plantarflexion, and plantargrade and repeated in these positions with a 5 N·m torque, simulating increased hindfoot valgus. The pressure sensor was removed and the PT and AT marked with ink at the same level, with the foot held in neutral rotation and plantargrade. Videos and photographs were taken to assess differential motion between the tendons. After testing, specimens were dissected to identify the PT insertion. One-way analysis of variance and paired t tests were performed to make comparisons. Results: The PT tendons with an insertion separate from the AT demonstrated greater differential motion through range (14 ± 4 mm) when compared with those directly adherent to the AT (2 ± 2 mm) (P < .001). Mean pressure between the PT and AT rose in terminal plantarflexion for all specimens (P < .001) and was more pronounced with hindfoot valgus (P < .001). Conclusion: The PT inserting directly into the calcaneus resulted in significantly greater differential motion as compared with the AT. Tendon compression was elevated in terminal plantarflexion, suggesting that adapting rehabilitation tendon-loading programs to avoid this position may be beneficial. Clinical Relevance: The insertion pattern of the PT may be a factor in plantaris-related midportion Achilles tendinopathy. Terminal range plantarflexion and hindfoot valgus both increased AT and PT compression, suggesting that these should be avoided in this patient population. [ABSTRACT FROM AUTHOR]

The aim of this study was to analyse lower limb work patterns in world-class race walkers. Seventeen male and female athletes race walked at competitive pace. Ground reaction forces (1000 Hz) and highspeed videos (100 Hz) were recorded and normalised joint moments, work and power, stride length, stride frequency and speed estimated. The hip flexors and extensors were the main generators of energy (24.5 J (±6.9) and 40.3 J (±8.3), respectively), with the ankle plantarflexors (16.3 J (±4.3)) contributing to the energy generated during late stance. The knee generated little energy but performed considerable negative work during swing (-49.1 J (±8.7)); the energy absorbed by the knee extensors was associated with smaller changes in velocity during stance (r = .783, P < .001), as was the energy generated by the hip flexors (r = -.689, P = .002). The knee flexors did most negative work (-38.6 J (±5.8)) and the frequent injuries to the hamstrings are probably due to this considerable negative work. Coaches should note the important contributions of the hip and ankle muscles to energy generation and the need to develop knee flexor strength in reducing the risk of injury. [ABSTRACT FROM AUTHOR]

Introduction: The muscle stretch intensity imposed during "flexibility" training influences the magnitude of joint range of motion (ROM) adaptation. Thus, stretching while the muscle is voluntarily activated was hypothesized to provide a greater stimulus than passive stretching. The effect of a 6-wk program of stretch imposed on an isometrically contracting muscle (i.e., qualitatively similar to isokinetic eccentric training) on muscle--tendon mechanics was therefore studied in 13 healthy human volunteers. Methods: Before and after the training program, dorsiflexion ROM, passive joint moment, and maximal isometric plantarflexor moment were recorded on an isokinetic dynamometer. Simultaneous real-time motion analysis and ultrasound imaging recorded gastrocnemius medialis muscle and Achilles tendon elongation. Training was performed twice weekly and consisted of five sets of 12 maximal isokinetic eccentric contractions at 10°-s-1. Results: Significant increases (P < 0.01) in ROM (92.7% [14.7-]), peak passive moment (i.e., stretch tolerance; 136.2%), area under the passive moment curve (i.e., energy storage; 302.6%), and maximal isometric plantarflexor moment (51.3%) were observed after training. Although no change in the slope of the passive moment curve (muscle-tendon stiffness) was detected ( -1.5%, P < 0.05), a significant increase in tendon stiffness (31.2%, P < 0.01) and a decrease in passive muscle stiffness (-14.6%, P < 0.05) were observed. Conclusion: The substantial positive adaptation in multiple functional and physiological variables that are cited within the primary etiology of muscle strain injury, including strength, ROM, muscle stiffness, and maximal energy storage, indicate that the stretching of active muscle might influence injury risk in addition to muscle function. The lack of change in muscle--tendon stiffness simultaneous with significant increases in tendon stiffness and decreases in passive muscle stiffness indicates that tissue-specific effects were elicited. [ABSTRACT FROM AUTHOR]

Background/Aims: Muscle maximum voluntary force declines at skin temperature <20°C, attributed to cold muscle, however large muscle deep fibres remain at >20°C. Large muscle maximum voluntary force decline is comparable to that in small superficial muscle where muscle temperature remains close to skin temperature. Therefore, factors in addition to temperature may contribute to large muscle maximum voluntary force decline. This study compares the effects of foot and/or shank skin temperature on dorsiflexion and plantarflexion maximum voluntary force with the hypotheses that: dorsiflexion maximum voluntary force>plantarflexion maximum voluntary force decline at lower skin temperature; and, plantarflexion and dorsiflexion maximum voluntary force will decline at lower shank skin temperature independent of foot skin temperature. Methods: A total of 24 adults (15 females, 9 males, 29 ± 11.8 years, 170.1 ± 8.0 cm, 66.9 ± 9.3 kg [mean ± standard deviation]) gave informed consent to participate on three visits – cooling/warming of: foot only; foot and shank; and shank only. Foot and/or shank temperature was adjusted using Cryocuff™ sleeves filled with ~45°C or ~4°C water. Temperature, taken before each maximum voluntary force set, was monitored through thermocouples placed on the limb. Plantarflexion and dorsiflexion maximum voluntary force were measured with a KinCom isokinetic dynamometer, with subjects seated on a plinth with knee fully extended and neutral ankle. A general mixed model was used to evaluate the effects of skin temperature on maximum voluntary force. Fixed effects were skin temperature and condition, with subject as a random effect. The skin temperature*condition interaction was also modelled. P-values were obtained by likelihood ratio tests. Results: Foot skin temperature <18.5°C resulted in a 10% (χ2(1)=5.479, P=0.019) dorsiflexion maximum voluntary force decline, with a skin temperature*condition interaction (χ2(2)=11.031, P=0.004), this decline was 12% (χ2(1)=13.18, P=0.0003) in foot only and 8% (χ2(1)=4.675, P=0.031) in foot and shank. Leg skin temperature did not affect (χ2(1)=2.849, P=0.091) dorsiflexion maximum voluntary force. Plantarflexion maximum voluntary force did not change with foot skin temperature (χ2(1)=0.04, P=0.841) or leg skin temperature (χ2(1)=0.082, P=0.929). Conclusions: Dorsiflexion maximum voluntary force declines at lower foot skin temperature independently of shank skin temperature, whereas plantarflexion maximum voluntary force is unaffected by skin temperature, possibly because in this protocol the shank was insufficiently cooled. Therefore factors other than direct muscle cooling must contribute to dorsiflexion maximum voluntary force decline. One theory is a rightward shift in the force-length relationship, due to stiffer tendon, could result in dorsiflexions operating in the descending limb of the force-length relationship. This warrants further investigation. [ABSTRACT FROM AUTHOR]