Developmental stage and lower quadriceps flexibilities and decreased gastrocnemius flexibilities are predictive risk factors for developing Osgood-Schlatter disease in adolescent male soccer players.

PURPOSE: This study aimed to elucidate the influential predictive risk factors of Osgood-Schlatter disease (OSD) on the support (non-kicking) leg among adolescent soccer players considering peak height velocity (PHV) age and investigate the cut-off values of the predictive variables. METHODS: A cohort of 302 Japanese adolescent male soccer players aged 12-13 years were followed over 6 months. All players underwent physical examination, tibial tubercle ultrasonography, anthropometric and whole-body composition measurements, and muscle flexibility test of the support leg at the baseline. The developmental stage was evaluated from the PHV age. The OSD of the support leg was diagnosed 6 months later; players were divided into the OSD and control (CON) groups. The predictive risk factors were analyzed by multivariate logistic regression analysis. RESULTS: There were 42 players who had developed OSD at baseline and they were excluded from the study. Among the 209 players, 43 and 166 belonged to the OSD and CON groups, respectively. The predictive risk factors of OSD development were PHV age ± 6 months at baseline (p = 0.046), apophyseal stage of tibial tuberosity maturity at baseline (p < 0.001), quadriceps flexibility ≥ 35° at baseline (p = 0.017), and decrease in gastrocnemius flexibility in 6 months (p = 0.009). CONCLUSION: PHV age ± 6 months at baseline, apophyseal stage of the tibial tuberosity at baseline, quadriceps flexibility ≥ 35° at baseline, and decrease in gastrocnemius flexibility in 6 months are predictive risk factors of OSD development in the support leg among adolescent male soccer players. It is crucial to know the PHV age of each player, and not only the flexibility of quadriceps muscle but also the gastrocnemius should be monitored to predict OSD. LEVEL OF EVIDENCE: II.

Is Increased Kicking Leg Iliopsoas Muscle Tightness a Predictive Factor for Developing Spondylolysis in Adolescent Male Soccer Players?

OBJECTIVE: To identify predictive risk factors of lumbar stress (LS) fracture developing from an asymptomatic stress reaction of the pedicle among adolescent male soccer players. DESIGN: Prospective cohort study. SETTING: Amateur Japanese adolescent male soccer team. PARTICIPANTS: Japanese adolescent male soccer players (n = 195) aged 12 to 13 years. ASSESSMENT OF RISK FACTORS INDEPENDENT VARIABLES: Height, body weight, body mass index, muscle tightness of both lower extremities (iliopsoas, hamstrings, and quadriceps), lumbar bone mineral content, developmental age, and lumbar lordosis angle were measured as baseline measurements. MAIN OUTCOME MEASURES DEPENDENT VARIABLE: Players who were diagnosed with an asymptomatic stress reaction of the lumbar spine pedicle at baseline were followed; extension-based lumbar pain was defined 1 year after the baseline. The players were assigned to the LS fracture or control (CON) group at follow-up. RESULTS: At baseline, 40 boys were diagnosed with an asymptomatic stress reaction of the lumbar spine pedicle. The difference in muscle tightness between the kicking leg and supporting leg was significantly different (P = 0.012) between the LS (n = 16) and CON (n = 22) groups. Increase in iliopsoas muscle tightness in the kicking leg was a predictive risk factor of developing extension-based lumbar pain after adjusting for developmental age and body mass index (odds ratio, 1.54; 95% confidence interval, 1.05-2.27). CONCLUSIONS: Development of extension-based lumbar pain from an asymptomatic stress reaction of the pedicle among adolescent male soccer players was associated with increased iliopsoas muscle tightness of the kicking leg relative to that of the supporting leg.

Force Generation on the Hallux Is More Affected by the Ankle Joint Angle than the Lesser Toes: An In Vivo Human Study.

The structure of the first toe is independent of that of the other toes, while the functional difference remains unclear. The purpose of this study was to investigate the difference in the force generation characteristics between the plantar-flexion of the first and second-fifth metatarsophalangeal joints (MTPJs) by comparing the maximal voluntary plantar-flexion torques (MVC torque) at different MTPJs and ankle positions. The MVC torques of the first and second-fifth MTPJs were measured at 0°, 15°, 30°, and 45° dorsiflexed positions of the MTPJs, and at 20° plantar-flexed, neutral, and 20° dorsiflexed positions of the ankle. Two-way repeated measures analyses of variance with Holm's multiple comparison test (MTPJ position × ankle position) were performed. When the MTPJ was dorsiflexed at 0°, 15°, and 30°, the MVC torque of the first MTPJ when the ankle was dorsiflexed at 20° was higher than that when the ankle was plantar-flexed at 20°. However, the ankle position had no significant effect on the MVC torque of the second-fifth MTPJ. Thus, the MVC torque of the first MTPJ was more affected by the ankle position than the second-fifth MTPJs.

Acute effects of difference in glucose intake on arterial stiffness in healthy subjects.

BACKGROUND: Post-prandial hyperglycemia is associated with higher cardiovascular risk, which causes arterial stiffening and impaired function. Although post-prandial increases in blood glucose are proportional to the level of intake, the acute effects of different glucose intakes on arterial stiffness have not been fully characterized. The present study aimed to determine the acute effects of differences in glucose intake on arterial stiffness. METHODS: Six healthy middle-aged and elderly individuals (mean age, 60.0 ± 12.1 years) were orally administered 15, 20, and 25 g of glucose on separate days in a randomized, controlled, cross-over fashion. Brachial-ankle pulse wave velocity, heart-brachial pulse wave velocity, cardio-ankle vascular index, brachial and ankle blood pressure, heart rate, and blood glucose and serum insulin concentrations before and 30, 60, and 90 min after glucose ingestion were measured. RESULTS: Compared to baseline, brachial-ankle pulse wave velocity was higher at 30, 60 and 90 min after ingestion of 25 g glucose, and higher at 90 min after ingestion of 20 g glucose, but at no time points after ingestion of 15 g. Cardio-ankle vascular index was higher at 60 min than at baseline after ingestion of 25 g glucose, but not after ingestion of 15 or 20 g. CONCLUSIONS: These results suggest that brachial-ankle pulse wave velocity and cardio-ankle vascular index is affected by the quantity of glucose ingested. Proposed presently is that glucose intake should be reduced at each meal to avoid increases in brachial-ankle pulse wave velocity and cardio-ankle vascular index during acute hyperglycemia.

Effects of a short-term increase in physical activity on arterial stiffness during hyperglycemia.

We examined the effects of increasing physical activity on arterial stiffness during hyperglycemia. Nineteen glucose-intolerant elderly participated in the study. We randomly assigned 10 participants to increase their daily activity in everyday life, regardless of the time or intensity, for 1 month (PAI group) (age, 74.6 ± 1.3 years; mean ± SE) and nine participants to maintain their level of activity (CON group) (age, 79.2 ± 2.1 years; mean ± SE). The 75-g oral glucose tolerance test was conducted in each participant in both groups before and after the start of the intervention to confirm glucose intolerance. Brachial-ankle pulse wave velocity and cardio-ankle vascular index significantly increased from baseline at 30, 60, and 90 min after the 75-g glucose ingestion after the intervention in the CON group (p<0.05), but not in the PAI group. Heart-brachial pulse wave velocity did not change compared to baseline after the 75-g glucose ingestion in either group and did not change from baseline at 30, 60, and 90 min after the 75-g glucose ingestion before and after the intervention in both groups. The present findings indicate that a short-term increase in physical activity suppresses the increase in arterial stiffness after glucose intake.

Effects of different intensities and durations of aerobic exercise training on arterial stiffness.

[Purpose] In the present study, we investigated the effects of regular aerobic training with different intensities and durations on new indices of arterial stiffness measured via an upper-arm oscillometric device. [Participants and Methods] We gathered data from 41 middle-aged and older people (age 65.0 ± 11.7 years). Participants were randomly divided into five groups: (1) 15 minutes of low intensity aerobic training (n=10); (2) 30 minutes of low intensity training (n=7); (3) 15 minutes of moderate-intensity training (n=9); (4) 30 minutes of moderate-intensity training (n=8); and (5) a non-training group (n=7). Training was conducted for 8 weeks, three times per week. Arterial pulse wave index, arterial pressure-volume index, brachial-ankle and heart-brachial pulse wave velocity, cardio-ankle vascular index, brachial and ankle blood pressure, heart rate, and peak oxygen uptake were measured before and after the intervention. [Results] All indicators of arterial stiffness and brachial and ankle blood pressure in the exercise groups were significantly lower after versus before the intervention. Peak oxygen uptake did not differ before versus after the intervention. [Conclusion] The present findings indicate that regular aerobic exercise may be important in reducing arterial stiffness regardless of the intensity or duration of aerobic exercise.

Arterial stiffness during hyperglycemia in older adults with high physical activity vs low physical activity.

We compared arterial stiffness after glucose intake in active and inactive elderly people with impaired glucose tolerance and clarified whether physical activity was associated with arterial stiffness after ingestion of glucose. Twenty older adults with impaired glucose tolerance were analyzed in a cross-sectional design. Based on the international physical activity questionnaire, participants were divided into the active group (daily step count: 10,175.9 ± 837.8 steps/day, n = 10) or the inactive group (daily step count: 4,125.6 ± 485.9 steps/day, n = 10). Brachial-ankle (systemic) and heart-brachial (aortic) pulse wave velocity and cardio-ankle vascular index (systemic) were increased at 30, 60, and 90 min compared to baseline after a 75-g oral glucose tolerance test in the inactive but not the active group. Heart-brachial pulse wave velocity did not change compared to baseline after a 75-g oral glucose tolerance test in either group. The area under the curve for brachial-ankle pulse wave velocity was associated with daily living activity (r = -0.577, p = 0.008), daily step activity (r = -0.546, p = 0.013), and the daily step count (r = -0.797, p = 0.0001). The present findings indicate that physical activity or inactivity is associated with arterial stiffness following glucose ingestion.

New indices of arterial stiffness measured with an upper-arm oscillometric device in active versus inactive women.

Arterial velocity pulse index (AVI) and arterial pressure-volume index (API), new indicators of arterial stiffness, are risk factors for the development of cardiovascular disease. Regular aerobic exercise decreases arterial stiffness. In fact, pulse wave velocity (PWV), index of arterial stiffness, is lower in endurance-trained than in untrained young adults. However, the effect of regular aerobic exercise on AVI and API remains unknown. This study investigates the effect of regular aerobic exercise on AVI and API, new indicators of arterial stiffness. We gathered data from 18 recreationally active females (active group, age: 18 ± 1 years, 2 ± 2 h/week, 3 ± 2 times/week, ≥2 years of aerobic endurance training) and 18 recreationally inactive females (inactive group, age: 18 ± 1 years, ≥2 years without such training) in a cross-sectional study. Height, body weight, body mass index, AVI, API, brachial blood pressure, heart rate, and 20-m multistage shuttle run test were measured in a quiet room at a temperature between 24°C and 25°C. AVI and API were lower in the active group than in the inactive group (P < 0.01). Number of 20-m shuttles was negatively correlated with AVI (P < 0.01, r = -0.8) and API (P < 0.01, r = -0.8). These results suggest that regular aerobic exercise training decreases AVI and API in young females.

Plyometric Training Favors Optimizing Muscle-Tendon Behavior during Depth Jumping.

The purpose of the present study was to elucidate how plyometric training improves stretch-shortening cycle (SSC) exercise performance in terms of muscle strength, tendon stiffness, and muscle-tendon behavior during SSC exercise. Eleven men were assigned to a training group and ten to a control group. Subjects in the training group performed depth jumps (DJ) using only the ankle joint for 12 weeks. Before and after the period, we observed reaction forces at foot, muscle-tendon behavior of the gastrocnemius, and electromyographic activities of the triceps surae and tibialis anterior during DJ. Maximal static plantar flexion strength and Achilles tendon stiffness were also determined. In the training group, maximal strength remained unchanged while tendon stiffness increased. The force impulse of DJ increased, with a shorter contact time and larger reaction force over the latter half of braking and initial half of propulsion phases. In the latter half of braking phase, the average electromyographic activity (mEMG) increased in the triceps surae and decreased in tibialis anterior, while fascicle behavior of the gastrocnemius remained unchanged. In the initial half of propulsion, mEMG of triceps surae and shortening velocity of gastrocnemius fascicle decreased, while shortening velocity of the tendon increased. These results suggest that the following mechanisms play an important role in improving SSC exercise performance through plyometric training: (1) optimization of muscle-tendon behavior of the agonists, associated with alteration in the neuromuscular activity during SSC exercise and increase in tendon stiffness and (2) decrease in the neuromuscular activity of antagonists during a counter movement.

Determination of contraction-induced changes in elbow flexor cross-sectional area for evaluating muscle size-strength relationship during contraction.

The aims of this study were to determine contraction-induced changes in the elbow flexor cross-sectional area (CSA) and to examine whether the maximal CSA during a high-intensity contraction is more closely related to the strength than that at rest in the elbow flexors. Fourteen young male subjects participated in this study. The elbow flexor CSAs were measured at sites from 1 cm proximal to 6 cm distal to the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) (every 1 cm; 8 sampling sites) using magnetic resonance imaging, at rest and during 10, 20, 40, 60, and 80% of maximal voluntary contraction (MVC) of isometric elbow flexion. The elbow flexor CSA changed greatly during low-intensity contractions, and this contraction-induced change was small over 60%MVC. Compared with at rest, greater CSA around the muscle belly and smaller CSA in the distal portion of the elbow flexors were found in contracted conditions. The MVC strength was significantly correlated with the maximal CSAs at rest and each contraction level, but stepwise multiple regression analysis selected only that during 80%MVC as a significant contributor for estimating the MVC strength. These results suggest that, in the elbow flexors, the contraction-induced change in the CSA reaches its peak under high contractile level and that the maximal CSA during 80%MVC is more closely related to the MVC strength than that at rest.

The contraction-induced increase in Achilles tendon moment arm: a three-dimensional study.

The present study aimed to re-examine the influence of the isometric plantarflexors contraction on the Achilles tendon moment arm (ATMA) and the factors influencing the ATMA in three-dimensions. A series of coronal magnetic resonance images of the right ankle were recorded at foot positions of 10° of dorsiflexion, neutral position, and 10° of plantarflexion for the rest condition and the plantarflexors contraction condition at 30% maximal voluntary effort. The shortest distance between the talocrural joint axis and the line of action of the Achilles tendon force projected to the orthogonal plane of the talocrural joint axis was determined as the ATMA. The ATMA determined in the contraction condition was significantly greater by 8mm than that determined in the rest condition. The talocrural joint axis was displaced anteriorly by 3mm and distally by 2mm due to the muscle contraction. As the same time, the line of action of the Achilles tendon force was displaced posteriorly by 5mm and medially by 2mm. These linear displacements of the talocrural joint axis and the line of action of the Achilles tendon force accounted for the difference in the ATMAs between the two conditions by 35.9 and 62.4%, respectively. These angular displacements accounted for the total of 0.4% increase in the ATMA. These results confirm the previous findings reported in two-dimensional studies and found that the linear displacement of the line of action of the Achilles tendon force is the primary source of the contraction-induced increase in the ATMA.

Association between contraction-induced increases in elbow flexor muscle thickness and distal biceps brachii tendon moment arm depends on the muscle thickness measurement site.

The purpose of this study was to investigate how the contraction-induced increase in distal biceps brachii tendon moment arm is related to that in elbow flexor muscle thickness, with a specific emphasis on the influence of the site-related differences in muscle thickness. The moment arm and muscle thickness were determined from sagittal and cross-sectional images, respectively, of the right arm obtained by magnetic resonance imaging of nine young men. The muscle thickness was measured at levels from the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) to 60 mm distal to it (every 10 mm; 7 measurement sites). At 80° of elbow flexion, the moment arm and muscle thickness were determined at rest and during 60% of maximal voluntary contraction (60%MVC) of isometric elbow flexion. Only the relative change from rest to 60%MVC in muscle thickness at the level 60 mm distal to the reference site correlated significantly with that of the moment arm. This result indicates that the contraction-induced increase in distal biceps brachii tendon moment arm is related to that in elbow flexor muscle thickness near the corresponding muscle-tendon junction.

In vivo measurements of moment arm lengths of three elbow flexors at rest and during isometric contractions.

The purpose of this study was to determine in vivo moment arm lengths (MAs) of three elbow flexors at rest and during low- and relatively high-intensity contractions, and to examine the contraction intensity dependence of MAs at different joint positions. At 50°, 80° and 110° of elbow flexion, MAs of the biceps brachii, brachialis and brachioradialis were measured in 10 young men using sagittal images of the right arm obtained by magnetic resonance imaging, at rest and during 20% and 60% of isometric maximal voluntary elbow flexion. In most conditions, MAs increased with isometric contractions, which is presumably due to the contraction-induced thickening of the muscles. This phenomenon was especially evident in the flexed elbow positions. The influence of the contraction intensities on the increases in MAs varied across the muscles. These results suggest that in vivo measurements of each elbow flexor MA during contractions are essential to properly examine the effects on the interrelationships between elbow flexion torque and individual muscle forces.

In vivo determination of the Achilles tendon moment arm in three-dimensions.

Two-dimensional methods have been applied to determine the Achilles tendon moment arm in previous studies, although the talocrural joint rotates in three-dimension. The purpose of this study was to develop a method for determining the Achilles tendon moment arm in three-dimensions (3DMA). A series of sagittal ankle images were obtained at ankle positions of -20°, -10° (dorsiflexed position), 0° (neutral position), +10°, +20°, and +30° (plantarflexed position). The talocrural joint axis was determined as the finite helical axis of the ankle joint over 20° of displacement, and the 3DMA was determined as the shortest distance from the talocrural joint axis to the line of action of the Achilles tendon force. The corresponding 2DMA was determined with the center of rotation method using the images captured on the sagittal plane passing through the mid-point of the medio-lateral width of the tibia. The 3DMA ranged from 35 to 41 mm across various ankle positions and was, on average, 11 mm smaller than 2DMA. The difference between the two measures was attributable primarily to the deviations of the talocrural joint axis from the anatomical medio-lateral direction. The deviations on the coronal plane (21.4±20.7°) and on the transverse planes (14.8±22.6°) accounted for the errors of 1.3 mm and 3.0 mm, respectively. In addition, selecting either a medially or laterally misaligned sagittal-plane image for determining the 2DMA gave rise to error by 3.5 mm. The remaining difference was accounted for by the random measurement error.

Methodological issues related to thickness-based muscle size evaluation.

The purpose of this study was to highlight the issues related to thickness-based muscle size evaluation that is commonly done in field studies. The cross-sectional area, thickness (the vertical distance from the upper end of the elbow flexors to that of the humerus) and width (the horizontal distance from the left to the right end of the elbow flexors) of the elbow flexors at levels from the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) to 5 cm distal to it were determined in 11 young men using magnetic resonance imaging, both at rest and during isometric elbow flexion at 30% of maximal voluntary contraction. During 30% of maximal voluntary contraction, the thickness increased but the width decreased at each measurement site compared with those at rest. This was possibly due to difference in muscle slackness between both conditions. The correlation coefficients between the thickness and cross-sectional area for the elbow flexors were significantly lower at rest (r=0.551-0.856) than during 30% of maximal voluntary contraction (r=0.711-0.922). The present findings indicate that the thickness-based muscle size measurement at rest includes errors owing to the slackness of the resting muscles.

Triceps surae muscle-tendon unit length changes as a function of ankle joint angles and contraction levels: the effect of foot arch deformation.

The purpose of this study was to clarify how foot deformation affects the relationship between triceps surae muscle-tendon unit (MTU) length and ankle joint angle. For six women and six men a series of sagittal magnetic resonance (MR) images of the right foot were taken, and changes in MTU length (the displacement of the calcaneal tuberosity), foot arch angle, and ankle joint angle were measured. In the passive session, each subject's ankle joint was secured at 10° dorsiflexed position, neutral position (NP), and 10° and 20° plantar flexed positions while MR images were acquired. In the active session, each subject was requested to perform submaximal isometric plantar flexions (30%, 60%, and 80% of voluntary maximum) at NP. The changes in MTU length in each trial were estimated by two different formulae reported previously. The changes of the measured MTU length as a function of ankle joint angles observed in all trials of the active session were significantly (p<0.05) larger than corresponding values in the passive session and by the estimation formulae. In the passive session, MTU length changes were significantly smaller than the estimated values when the ankle was plantar flexed. The foot arch angle increased as the contraction level increased from rest (117 ± 4°) to 80% (125 ± 3°), and decreased as the ankle was positioned further into plantar flexion in the passive session (115 ± 3°). These results indicate that foot deformation profoundly affects the triceps surae MTU length-ankle joint angle relationship during plantar flexion.

Longitudinal and transverse deformation of human Achilles tendon induced by isometric plantar flexion at different intensities.

The present study determined in vivo deformation of the entire Achilles tendon in the longitudinal and transverse directions during isometric plantar flexions. Twelve young women and men performed isometric plantar flexions at 0% (rest), 30%, and 60% of the maximal voluntary contraction (MVC) while a series of oblique longitudinal and cross-sectional magnetic resonance (MR) images of the Achilles tendon were taken. At the distal end of the soleus muscle belly, the Achilles tendon was divided into the aponeurotic (ATapo) and the tendinous (ATten) components. The length of each component was measured in the MR images. The widths of the Achilles tendon were determined at 10 regions along ATapo and at four regions along ATten. Longitudinal and transverse strains were calculated as changes in relative length and width compared with those at rest. The ATapo deformed in both longitudinal and transverse directions at 30%MVC and 60%MVC. There was no difference between the strains of the ATapo at 30%MVC and 60%MVC either in the longitudinal (1.1 and 1.6%) or transverse (5.0∼11.4 and 5.0∼13.9%) direction. The ATten was elongated longitudinally (3.3%) to a greater amount than ATapo, while narrowing transversely in the most distal region (-4.6%). The current results show that the magnitude and the direction of contraction-induced deformation of Achilles tendon are different for the proximal and distal components. This may be related to the different functions of Achilles tendon, i.e., force transmission or elastic energy storage during muscle contractions.