Effects of acupuncture and acupressure of the acupoint compared to the tendon on the blood circulation of human tendon in vivo.

PURPOSE: The purpose of this study was to compare the effects of acupuncture and acupressure of acupoints on tendon blood circulation with those of both types of stimulation of tendon itself. METHODS: Before, during (except for acupressure), and after acupuncture and acupressure of the tendon and acupoint, blood circulation of the Achilles tendon was measured using red laser lights. RESULTS: The blood volume of the treated and non-treated tendons increased after acupuncture of the tendon (effect of time p = 0.030), whereas that tended to increase after acupuncture of the acupoint (effect of time p = 0.063). In addition, no significant difference in the increases in blood volume was found among the four conditions, i.e., after acupuncture stimulation of the tendon and acupoint for the treated and non-treated tendons (p = 0.492). The blood volume of the treated tendon significantly increased after acupressure of the tendon (effect of time p < 0.001), but not of the acupoint (effect of time p = 0.260), whereas that of the non-treated tendon did not change after acupressure of both the tendon and acupoint. CONCLUSION: These results suggested that acupuncture of the tendon and acupoint acted centrally to enhance blood circulation of both the treated and non-treated tendons during the recovery period, whereas acupressure of the tendon locally increased blood circulation of the treated tendon only, but not the non-treated tendon and both the treated and non-treated tendons after acupressure of acupoint.

Effect of Static Stretching on Tendon Hysteresis and Efficiency During Repetitive Jumping.

ABSTRACT: Sasajima, S and Kubo, K. Effect of static stretching on tendon hysteresis and efficiency during repetitive jumping. J Strength Cond Res 38(6): 1041-1047, 2024-To date, no studies have experimentally shown a relationship between tendon hysteresis and exercise efficiency. However, previous studies showed that tendon hysteresis decreased immediately after static stretching. The purposes of this study were to (a) investigate the change in tendon hysteresis during the recovery period after static stretching and (b) determine whether exercise efficiency is enhanced because of the decline of tendon hysteresis after static stretching. For stretching (1 minute × 4 sets) and control conditions, tendon hysteresis was measured during ramp (i.e., lower strain rate of tendon) and ballistic (i.e., higher strain rate of tendon) contractions before, immediately, 15, 30, 45, and 60 minutes after interventions. In addition, electromyograms of the plantar flexor muscles (medial gastrocnemius [MG], lateral gastrocnemius [LG], and soleus muscles [SOL]) and oxygen consumption (V̇O 2 ) were measured during 10 minutes of submaximal repetitive jumping after both interventions. Tendon hysteresis (during ramp and ballistic contractions) reduced by static stretching persisted for up to 60 minutes (effect of time p < 0.001). During repetitive jumping, no differences in electromyograms of the plantar flexor muscles (effect of condition p = 0.786 for MG, p = 0.124 for LG, p = 0.682 for SOL) or V̇O 2 (effect of condition p = 0.534) were found between stretching and control conditions. These results suggest that the reduction in tendon hysteresis because of static stretching continues until 60 minutes after the end of stretching, and static stretching does not change the efficiency (evaluated by electromyograms of the plantar flexor muscles and V̇O 2 ) during submaximal repetitive jumping.

Androgen receptor suppresses ß-adrenoceptor-mediated CREB activation and thermogenesis in brown adipose tissue of male mice.

Thermoregulation is a process by which core body temperature is maintained in mammals. Males typically have a lower body temperature than females. However, the effects of androgens, which show higher levels in males, on adrenergic receptor-mediated thermogenesis remain unclear. Here, we demonstrate that androgen-androgen receptor (AR) signaling suppresses the ß-adrenergic agonist-induced rise of core body temperature using castrated and AR knockout (ARKO) male mice. Furthermore, in vitro mechanistic studies show that activated AR inhibits cAMP response element (CRE)-mediated transcription by suppressing cAMP response element-binding protein (CREB) phosphorylation. The elevation of body temperature induced by the ß-adrenergic agonist CL316243 was higher in ARKO and castrated mice than in the control mice. Similarly, CL316243 induced a greater increase in Uncoupling protein 1 (Ucp1) expression and CREB phosphorylation in the brown adipose tissue of ARKO mice than in that of controls. We determined that activation of AR by dihydrotestosterone suppressed ß3-agonist- or forskolin-induced CRE-mediated transcription, which was prevented by AR antagonist. AR activation also suppressed CREB phosphorylation induced by forskolin. Moreover, we found AR nuclear localization, but not transcriptional activity, was necessary for the suppression of CRE-mediated transcription. Finally, modified mammalian two-hybrid and immunoprecipitation analyses suggest nuclear AR and CREB form a protein complex both in the presence and absence of dihydrotestosterone and forskolin. These results suggest androgen-AR signaling suppresses ß-adrenoceptor-induced UCP1-mediated brown adipose tissue thermogenesis by suppressing CREB phosphorylation, presumably owing to a protein complex with AR and CREB. This mechanism explains sexual differences in body temperature, at least partially.

Effect of relaxation time on hysteresis of human tendon in vivo.

OBJECTIVES: The purpose of this study was to investigate the effect of relaxation time on tendon hysteresis. METHODS: Subjects exerted isometric plantar flexion torque from rest to maximal voluntary isometric contractions within around 0.5 s, followed by relaxation with six different times (0.3, 0.5, 0.7, 1, 3, and 5 s). During each trial, tendon elongation in the medial gastrocnemius muscle was measured by ultrasonography. The area within the exerted torque-tendon elongation loop, as a percentage of the area beneath the curve during ascending phase, was calculated as tendon hysteresis. RESULTS: Between the 0.3 and 1 s relaxation time conditions, the hysteresis values were significantly greater for the shorter relaxation time conditions (except between the 0.5 and 0.7 s conditions). In contrast, no significant differences in tendon hysteresis were found between 1 and 5 s of relaxation time conditions. Furthermore, the relationship between relaxation time and tendon hysteresis showed a significantly negative correlation under 1 s or less of relaxation time, but no significant correlation was observed under conditions of 1 s or more. CONCLUSION: These results suggest that relaxation time greatly affects tendon hysteresis under condition that relaxation time was less than 1 s.

A Longitudinal Study of the Physical Characteristics, Muscle-Tendon Structure Properties, and Skeletal Age in Preadolescent Boys.

OBJECTIVES: The purpose of this study was to examine longitudinal growth changes in physical characteristics, muscle-tendon structure properties, and skeletal age in preadolescent boys and to compare the relationship between the changes in physical characteristics and muscle-tendon properties and the changes in chronological and skeletal ages. METHODS: Fourteen prepubescent boys (10.9 ± 1.1 years old at the onset of the study) participated in this study over two years (yearly). Maximal muscle strength and maximal strain of tendon structure during ramp isometric contraction and muscle and tendon thickness for knee extensors and plantar flexors were measured. In addition, skeletal age was assessed using Tanner-Whitehouse three method. RESULTS: Changes in height, thigh length, and lower leg length were highly correlated with changes in skeletal age but not chronological age. However, changes in the morphological and mechanical properties of muscle and tendon structure were not significantly associated with changes in chronological and skeletal ages. CONCLUSION: The present preliminary results suggest that longitudinal growth changes in the long-axis of the body are highly correlated with skeletal age change, whereas those in the muscle-tendon structure properties were not.

Effects of tendon elastic energy and electromyographic activity pattern on jumping height and pre-stretch augmentation during jumps with different pre-stretch intensity.

The present study aimed to investigate the effects of tendon elastic energy and electromyographic activity patterns (ratio of pre-landing to concentric: mEMG PLA/CON; ratio of eccentric to concentric; mEMG ECC/CON) on jump performance. Twenty-nine males performed five kinds of unilateral jumps using only ankle joint (no-countermovement jump: noCMJ; countermovement jump: CMJ; drop jumps at 10, 20 and 30 cm drop height: DJ10, DJ20 and DJ30). Jumping height, pre-stretch augmentation and electromyographic activity of the plantar flexor muscles were measured. The elastic energy of the Achilles tendon was measured during isometric contractions. Relative tendon elastic energy (to body mass) was highly correlated with jumping heights of CMJ, DJ10 and DJ20 but not with noCMJ and DJ30, whereas that was significantly correlated with pre-stretch augmentation in CMJ, but not with three DJs. The mEMG PLA/CON was significantly correlated with the pre-stretch augmentation of DJ20 and DJ30, but not with DJ10, whereas the mEMG ECC/CON was significantly correlated with the pre-stretch augmentation of DJ20 and DJ30, but not with CMJ and DJ10. These results suggested that jumping exercises with low pre-stretch intensity benefited from tendon elastic energy, but those with high pre-stretch intensity benefited from electromyographic activity patterns.

Effect of Professional Denture Cleaning on Surface Roughness of Silicone or Acrylic Soft Relining Materials.

The aim of this study was to investigate the effects of combining mechanical (ultrasonic) and chemical cleaning (using denture cleaners) on the surface roughness of silicone or acrylic soft relining materials. The silicone soft relining material with the lowest Shore A hardness and a acrylic soft relining material routinely used in Japan were selected. Four groups were established based on type of treatment: immersion in water (W); ultrasonic cleaning in tap water (U); ultrasonic cleaning in a hypochlorous acid denture cleanser (HU); or ultrasonic cleaning in an acidic denture cleanser (AU). Following the tests, surface roughness was determined as the arithmetic mean height of the surface (Sa) and maximum height (Sz). Data were analyzed using the Kruskal-Wallis test followed by Bonferroni correction for a multiple comparison. No significant difference was observed in the Sa or Sz of the silicone soft relining material between the 4 groups. Significant differences were observed in the Sa of the acrylic soft relining material between Groups W and HU (p=0.008) and between Groups W and AU (p=0.008), but no significant differences in the Sz among the 4 groups. Combining U with AU or U with HU yielded no increase in the surface roughness of the silicon soft relining material. The surface roughness of the acrylic soft relining material showed an increase, however, with the combination treatments used.

Relationship between short latency stretch reflex and fascicle behavior in the soleus muscle in vivo.

OBJECTIVES: Stretch reflex responses were considered to be affected by the velocity of muscle fiber lengthening and angular velocity. However, the results of previous studies in vivo and in vitro are inconsistent in this regard. The purpose of the present study was to investigate the effects of the velocity of fascicle lengthening on the amplitude of the stretch reflex for each trial with a high angular velocity and wide range of motion. METHODS: Thirteen healthy men volunteered for this study. While the ankle was passively moved from 100 to 80 deg at five different angular velocities (100, 200, 300, 500, and 600 deg⋅s-1), the velocity of fascicle lengthening in the soleus muscle was measured using ultrasonography. In addition, the amplitude of the short latency stretch reflex in the soleus muscle was also measured. RESULTS: As angular velocity increased, the amplitude of the stretch reflex and velocity of fascicle lengthening significantly increased (both p<0.001). For each trial in all subjects, the amplitude of the stretch reflex was not correlated with the velocity of fascicle lengthening at any of the angular velocities. CONCLUSION: In conclusion, the stretch reflex size is not related to the fascicle behavior in each trial.

Effect of short latency stretch reflex on passive and active muscle stiffness in the soleus muscle in vivo.

PURPOSE: The purpose of the present study was to determine the effect of the short latency stretch reflex on passive and active muscle stiffness in the soleus muscle. METHODS: Fourteen males participated in this study. Passive muscle stiffness was calculated from passive muscle force and fascicle length during passive lengthening at four different angular velocities (5, 50, 100, and 200 deg s-1). Active muscle stiffness was also calculated according to changes in muscle force and fascicle length during fast lengthening at five different angular velocities (100, 200, 300, 500, and 600 deg s-1) after submaximal isometric contraction (30% of maximal voluntary contraction). During the measurements of passive and active muscle stiffness, the amplitude of the short latency stretch reflex in the soleus muscle was measured. RESULTS: Change in passive torque and passive muscle stiffness significantly increased, whereas change in the fascicle length decreased, as angular velocity increased. At 100 and 200 deg s-1 (stretch reflex responses were not observed at 5 and 50 deg s-1), the amplitude of the short latency stretch reflex was highly correlated with passive muscle stiffness. Change in torque and active muscle stiffness were highest at 100 deg s-1 and decreased as angular velocity increased. At all angular velocities under active conditions, the amplitude of the short latency stretch reflex was not correlated with active muscle stiffness. CONCLUSION: These results suggest that the short latency stretch reflex affects passive muscle stiffness in the soleus muscle, but not active muscle stiffness.

Effects of 4, 8, and 12 Repetition Maximum Resistance Training Protocols on Muscle Volume and Strength.

ABSTRACT: Kubo, K, Ikebukuro, T, and Yata, H. Effects of 4, 8, and 12 repetition maximum resistance training protocols on muscle volume and strength. J Strength Cond Res 35(4): 879-885, 2021-The purpose of this study was to determine skeletal muscle adaptations (strength and hypertrophy) in response to volume-equated resistance training with divergent repetition strategies. Forty-two men were randomly assigned to 4 groups: higher load-lower repetition group performing 4 repetition maximum (RM) for 7 sets (4RM, n = 10), intermediate load-intermediate repetition group performing 8RM for 4 sets (8RM, n = 12), lower load-higher repetition group performing 12RM for 3 sets (12RM, n = 10), and nonexercising control group (CON, n = 10). The volume of the pectoralis major muscle (by magnetic resonance imaging) and 1RM of the bench press were measured before and after 10 weeks of training (2 times per week). No significant difference was observed in the relative increase in the muscle volume among the 4RM, 8RM, and 12RM groups. The relative increase in 1RM was significantly lower in the 12RM group than in the 4RM group (p = 0.029) and the 8RM group (p = 0.021). The relative increase in 1RM was significantly correlated with that in the muscle volume in the 12RM group (r = 0.684, p = 0.042), but not in the 4RM (r = -0.265, p = 0.777) or 8RM (r = -0.045, p = 0.889) groups. These results suggest that the increase in muscle size is similar among the 3 training protocols when the training volume was equated, whereas the increase in muscle strength is lower with the 12RM protocol than the other protocols.

Retention force and allowable range of the angle of an implant-supported overdenture attachment system using healing screws and a silicone resilient denture liner.

STATEMENT OF PROBLEM: Changes in the intraoral condition immediately after implant placement and in patients using fixed prosthetic appliances with implant abutments cause problems that require the use of an easily adjustable implant-supported overdenture system. PURPOSE: The purpose of this in vitro study was to develop a simulated implant-supported overdenture attachment system by using healing screws for the patrix and a silicone resilient denture liner for the matrix and to investigate the initial retention force, time-course changes, and allowable range of the angle between attachments. MATERIAL AND METHODS: Tests on the retention force and allowable range of the angle were performed. Attachments using tissue-level healing screws (height: 2.0 and 3.0 mm) for the patrix and a silicone resilient denture liner for the matrix were prepared. In the retention force measurement test, the frequency of insertion and removal was set at 3 per day to simulate a 4-month relief period. The joined attachment model was pulled apart, and the maximum traction (N) required to remove it was defined as the retention force. The retention force was measured every 90 times (representing the number of insertions and removals per month). To test the allowable angle range, 2 patrices were used. The angle between the 2 patrices was set at 0, 10, 20, and 30 degrees, and the angular limit for joining with the matrix was measured. The initial retention force of the healing screw attachments was compared with that of a polymeric O-ring by using 1-way layout ANOVA followed by the Bonferroni test (α=.05). To analyze time-course changes in the 2 types of healing screw attachments, the retention force before insertion and removal was compared with that after repeated insertions and removals for each simulated period using 1-way layout ANOVA followed by the Dunnett test (α=.05). RESULTS: The initial retention force of the 2.0- and 3.0-mm healing screws was 2.4 ±0.1 and 2.6 ±0.2 N. After repeating insertions and removals to simulate use for 4 months, the retention force of the 2.0- and 3.0-mm healing screws was 1.8 ±0.2 and 2.2 ±0.1 N, respectively, both showing significant differences from the initial retention force (P<.05). The allowable angle range test revealed that insertion and removal of the healing screws was possible up to 30 degrees. CONCLUSIONS: Under the conditions of this in vitro study, repeated insertion and removal attenuated the retention force but was still equivalent to the retention force of the O-ring. The allowable range of the angle between patrices for insertion and removal was up to 30 degrees.

Effects of squat training with different depths on lower limb muscle volumes.

PURPOSE: The purpose of this study was to compare the effects of squat training with different depths on lower limb muscle volumes. METHODS: Seventeen males were randomly assigned to a full squat training group (FST, n = 8) or half squat training group (HST, n = 9). They completed 10 weeks (2 days per week) of squat training. The muscle volumes (by magnetic resonance imaging) of the knee extensor, hamstring, adductor, and gluteus maximus muscles and the one repetition maximum (1RM) of full and half squats were measured before and after training. RESULTS: The relative increase in 1RM of full squat was significantly greater in FST (31.8 ± 14.9%) than in HST (11.3 ± 8.6%) (p = 0.003), whereas there was no difference in the relative increase in 1RM of half squat between FST (24.2 ± 7.1%) and HST (32.0 ± 12.1%) (p = 0.132). The volumes of knee extensor muscles significantly increased by 4.9 ± 2.6% in FST (p < 0.001) and 4.6 ± 3.1% in HST (p = 0.003), whereas that of rectus femoris and hamstring muscles did not change in either group. The volumes of adductor and gluteus maximus muscles significantly increased in FST (6.2 ± 2.6% and 6.7 ± 3.5%) and HST (2.7 ± 3.1% and 2.2 ± 2.6%). In addition, relative increases in adductor (p = 0.026) and gluteus maximus (p = 0.008) muscle volumes were significantly greater in FST than in HST. CONCLUSION: The results suggest that full squat training is more effective for developing the lower limb muscles excluding the rectus femoris and hamstring muscles.

Effects of eccentric training with different training frequencies on blood circulation, collagen fiber orientation, and mechanical properties of human Achilles tendons in vivo.

PURPOSE: The purpose of the present study was to compare the effects of eccentric training with different training frequencies on the blood circulation, collagen orientation, and mechanical properties of the human Achilles tendon in vivo. METHODS: Ten healthy males completed 12 weeks of a unilateral eccentric training program {(15 repetitions with knee straight and 15 repetitions with knee slightly bent) × 6 sets in a single session} for the plantar flexor muscles. They performed training three times per week on one side (3TW) and six times per week on the other side (6TW). Before and after training, changes in blood volume, coefficient of variation (CV) of echogenicity (reflects collagen fiber orientation), and stiffness of the Achilles tendon were compared by two-way analysis of variance. RESULTS: The tendon blood volume tended to increase after 3TW and 6TW (p = 0.064). Tendon stiffness did not change after 3TW and 6TW, whereas the elongation of tendon structures at three force levels (50, 100, and 150 N) significantly decreased with 3TW, but not 6TW. The CV of echogenicity significantly decreased after 3TW and 6TW. However, no significant differences were observed in the relative changes in these measured variables between 3TW and 6TW. CONCLUSION: The present results demonstrated an increase in blood volume, the alignment of collagen fibers, and unchanged stiffness of the Achilles tendon after 12 weeks of eccentric training. Furthermore, the training frequency did not influence these training-induced changes in the tendon properties.

Influence of the mechanical properties of resilient denture liners on the retention of overdenture attachments.

STATEMENT OF PROBLEM: Information is lacking about the selection criteria for silicone resilient denture liners applied as a matrix material for attachments on overdentures. PURPOSE: The purpose of this in vitro study was to investigate the mechanical properties of silicone resilient denture liners and their influence on the initial retention force of overdenture attachments and the reduction in retention force over time. MATERIAL AND METHODS: Nine types of silicone resilient denture liner were injected and fixed to the matrix section of an experimental denture base. They were then fitted to an epoxy resin model that simulated the residual ridge with a patrix ball attachment (n=10). The retention force of the denture was measured with a digital force gauge, and the maximum force of traction (N) was regarded as the initial retention force. The retention force reduction (N) after repeated insertion and removal (n=5) was calculated by subtracting the retention force after 3348 cycles (3-year simulated insertion and removal) from the initial retention force. The intaglio of the matrix was observed with a scanning electron microscope (SEM) before and after the 3348 cycles. Four mechanical properties (hardness, strain-in-compression, tensile strength, and arithmetic mean roughness) of the resilient denture liners were measured. One-way ANOVA of the initial retention force of each lining material was performed, followed by the Scheffe test (α=.05). Pearson correlation analysis was used (α=.05) to analyze correlations of the initial retention force with the retention force reduction after insertion and removal and the mechanical properties of each material. Multiple regression analysis with the stepwise method extracted the initial retention force and the retention force reduction as dependent variables, and the resilient denture liner mechanical properties as explanatory variables (α=.05). RESULTS: The initial retention force of the resilient denture liners was 1.3 to 5.4 N. Multiple comparisons showed significant differences in some groups (P<.05). The retention force reduction of the resilient denture liners was 0.2 to 1.9 N. Multiple regression analysis with the stepwise method extracted hardness and strain-in-compression as explanatory variables for the initial retention force and the retention force reduction. CONCLUSIONS: Within the limitations of this in vitro study, hardness was found to influence the initial retention force of the overdenture, and strain-in-compression influenced the retention force reduction in the 3-year simulation.

Active muscle and tendon stiffness of plantar flexors in sprinters.

The aim of the present study was to investigate and compare muscle and tendon stiffness under active conditions in sprinters and untrained participants. In total, 14 sprinters and 24 untrained men participated in this study. Active muscle stiffness in the medial gastrocnemius muscle was calculated based on changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Tendon stiffness was determined during isometric plantar flexion using ultrasonography. No significant differences were observed in active muscle stiffness between sprinters and untrained men at any torque levels. Furthermore, no significant difference was noted in tendon stiffness between the two groups. These results suggest that muscle and tendon mechanical properties in the plantar flexors under active conditions are similar in sprinters and untrained participants.

Blood Supply.

It has been suggested that blood circulation within the tendons contributes to repair of the tendon after the exercises. Recently, blood circulation of human tendons could be measured using red laser lights (Kubo et al. 2008b). Using this technique, we were able to measure changes in blood volume and oxygen saturation of human tendons by various treatments. During a 60-min heating, the blood volume and oxygen saturation of the tendon increased significantly from the resting level, and continued to increase by 35 min. These changes in blood circulation of tendon were considerably different from the temperatures of muscle and skin. Furthermore, when the needle tip was moved up and down from the targeted depth (up-and-down manipulation) at approximately 1 mm amplitude, the blood volume and oxygen saturation of the treated tendon increased significantly. After the removal of the acupuncture needle, the blood volume and oxygen saturation of the tendon increased gradually for the non-treated side. These results suggested that the change in blood circulation of the tendon during acupuncture with up-and-down manipulation was caused by axon reflex, and increase in blood flow in the tendons after the needle removal might be caused through the central nervous system. It is well known that heating and acupuncture treatments were quite effective in the management of tendon injuries. Therefore, these phenomena would be related to the changes in blood circulation of tendons due to heating and acupuncture treatments.

Relationship between elastic properties of tendon structures and performance in long distance runners.

INTRODUCTION: The purpose of this study was to investigate the relationship between running performance (best official record in a 5000 m race) and elastic properties of tendon structures in knee extensors and plantar flexors among a large population of long distance runners. METHODS: Sixty-four highly trained male long distance runners participated in this study. Elongation of tendon structures in the knee extensors and plantar flexors was measured using ultrasonography while subjects performed ramp isometric contractions up to the voluntary maximum. The relationship between the estimated muscle force and tendon elongation was fit to a linear regression, the slope of which was defined as the stiffness of the tendon structures. Muscle and tendon thicknesses were also measured in the knee extensors and plantar flexors using ultrasonography. RESULTS: The best official record in a 5000 m race was negatively correlated to the stiffness of the tendon structures in the knee extensors (r = -0.341, p < 0.01), whereas it was positively correlated to the stiffness of the tendon structures in the plantar flexors (r = 0.414, p < 0.001). In both the knee extensors and plantar flexors, the other measured variables of muscle and tendon structures did not correlate with the best official record in a 5000 m race. CONCLUSION: These results suggested that better long distance runners had stiffer tendon structures in the knee extensors and more compliant ones in the plantar flexors. These results implied that tendon structures in knee extensors and plantar flexors adapted to endurance running training and contributed to running performance of long distance runners separately.

Relationship between Achilles tendon properties and foot strike patterns in long-distance runners.

The purpose of this study was to investigate the relationship between Achilles tendon properties and foot strike patterns in long-distance runners. Forty-one highly trained male long-distance runners participated in this study. Elongation of the Achilles tendon and aponeurosis of the medial gastrocnemius muscle were measured using ultrasonography, while the participants performed ramp isometric plantar flexion up to the voluntary maximum. The relationship between the estimated muscle force and tendon elongation during the ascending phase was fit to a linear regression, the slope of which was defined as stiffness. In addition, the cross-sectional area of the Achilles tendon was measured using ultrasonography. Foot strike patterns (forefoot, midfoot and rearfoot) during running were determined at submaximal velocity (18 km · h(-1)) on a treadmill. The number of each foot strike runner was 12 for the forefoot (29.3%), 12 for the midfoot (29.3%) and 17 for the rearfoot (41.5%). No significant differences were observed in the variables measured for the Achilles tendon among the three groups. These results suggested that the foot strike pattern during running did not affect the morphological or mechanical properties of the Achilles tendon in long-distance runners.

Growth changes in morphological and mechanical properties of human patellar tendon in vivo.

The purpose of this study was to compare the morphological and mechanical properties of the human patellar tendon among elementary school children (prepubertal), junior high school students (pubertal), and adults. Twenty-one elementary school children, 18 junior high school students, and 22 adults participated in this study. The maximal strain, stiffness, Young's modulus, hysteresis, and cross-sectional area of the patellar tendon were measured using ultrasonography. No significant difference was observed in the relative length (to thigh length) or cross-sectional area (to body mass(2/3)) of the patellar tendon among the three groups. Stiffness and Young's modulus were significantly lower in elementary school children than in the other groups, while no significant differences were observed between junior high school students and adults. No significant differences were observed in maximal strain or hysteresis among the three groups. These results suggest that the material property (Young's modulus) of the patellar tendons of elementary school children was lower than that of the other groups, whereas that of junior high school students was already similar to that of adults. In addition, no significant differences were observed in the extensibility (maximal strain) or viscosity (hysteresis) of the patellar tendon among the three groups.

Influence of preconditioning on morphological and mechanical properties of human Achilles tendon in vivo.

The present study aimed 1) to verify whether the effect of preconditioning was observed in the measured variables during the measurement of the human tendon in vivo (i.e., repeated contractions with breaks between trials) and 2) to determine the changes in tendon properties and their mechanisms due to submaximal repetitive contractions. Twelve healthy males participated in this study. To eliminate the effects of preconditioning, the participants rested on the measurement bed for 2 h before the start of both experiment-1 and experiment-2. In experiment-1, the measurements of elongation and hysteresis of the Achilles tendon for ramp and ballistic conditions were repeated ten times every 2 min. In experiment-2, participants performed submaximal repetitive contractions at 50 % of MVC and a frequency of 1 Hz for 10 min with a 30 s break every 2 min. Tendon mechanical properties were measured during contractions (starting 30 s and last 20 s of every 2 min), and the mean and coefficient variation (CV) of echogenicity were assessed during a 30-s rest every 2 min. In experiment-1, no significant differences in elongation and hysteresis of the tendon for ramp and ballistic contractions were found among the trials. In experiment 2, there were no significant differences in tendon elongation and hysteresis among all measurement times. Mean echogenicity increased significantly after 2 min, and CV of echogenicity decreased significantly after 4 min. These results suggest that preconditioning does not affect the elongation and hysteresis of the Achilles tendon in measuring tendon mechanical properties and submaximal repetitive contractions.