Elasticity of the Forearm Flexor-Pronator Muscles as a Risk Factor for Medial Elbow Injuries in Young Baseball Players: A Prospective Cohort Study of 314 Players.

BACKGROUND: Young baseball players with medial elbow injuries are known to have high forearm flexor-pronator muscle elasticity; however, the causal relationship between forearm muscle elasticity and the occurrence of medial elbow injuries remains unclear. PURPOSE/HYPOTHESIS: The purpose of this study was to determine whether the forearm flexor-pronator muscle elasticity is a risk factor for medial elbow injury in young baseball players. It was hypothesized that high flexor carpi ulnaris (FCU) elasticity would be a risk factor for medial elbow injuries. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Young baseball players (aged 9-12 years) with no history of elbow injuries underwent examination during which the strain ratios (SRs) of the pronator teres, flexor digitorum superficialis, and FCU muscles were measured using ultrasound strain elastography as an index of elasticity. Additionally, the participants completed a questionnaire assessing age, height, weight, months of experience as a baseball player, position in baseball, number of training days per week, number of throws per day, and elbow pain during throwing; then the range of motion of the shoulder and hip internal/external rotation were measured. One year after the baseline measurements, the occurrence of new medial elbow injuries was evaluated. Multivariate logistic regression analysis was subsequently conducted to determine risk factors for medial elbow injuries. Cutoff points for significant SR values obtained from the multivariate logistic regression analysis were calculated using the receiver operating characteristic curve. RESULTS: Of the 314 players, 76 (24.2%) were diagnosed with medial elbow injury. Multivariate logistic regression analysis showed that a 0.1 increase in the SR of the FCU muscle (odds ratio [OR], 1.211; 95% CI, 1.116-1.314) and number of throws per day (OR, 1.012; 95% CI, 1.001-1.022) were significantly associated with medial elbow injuries. Receiver operating characteristic curve analyses revealed that the optimal cutoff for the SR of the FCU muscle was 0.920 (area under the curve, 0.694; sensitivity, 75.0%; specificity, 56.7%). CONCLUSION: Increased FCU elasticity is a risk factor for medial elbow injury. Evaluation of the FCU elasticity may be useful in identifying young baseball players at high risk of medial elbow injuries and may facilitate prevention of medial elbow injury. As shown by the results of multivariate logistic regression analysis, FCU elasticity itself may be useful in identifying young baseball players at high risk of elbow injuries. However, we believe that other factors, such as the number of pitches per day, need to be considered to improve its accuracy.

Increased Medial Elbow Torque Is Associated With Ball Velocity Rather Than a History of Medial Elbow Injuries in Youth Baseball Pitchers.

PURPOSE: This study compared medial elbow torque in youth baseball pitchers with and without a history of medial elbow injuries to determine the relationship between medial elbow torque during pitching and having a history of medial elbow injuries. METHODS: We recruited 171 youth baseball pitchers aged 9 to 12 years old. The exclusion criteria included current pain with pitching, history of surgery on the tested extremity, or osteochondritis dissecans of the humeral capitellum. The participants were grouped into 3 groups: injury <1-year, injury >1-year, and control, based on ultrasonographic abnormalities of the elbow and the presence of elbow pain. Pitchers pitched 3 fastballs while wearing a sensor sleeve that recorded the medial elbow torque, arm speed, and shoulder rotation. Ball velocity was measured using a radar gun. RESULTS: The final analysis included 164 pitchers. Thirty were assigned to the injury <1-year group, 34 to the injury >1-year group, and 100 to the control group. The medial elbow torque was significantly greater in the injury <1-year group compared with the control group (18.6 ± 3.6 Nm vs 16.2 ± 4.8 Nm, P = .023). A multiple regression analysis revealed that ball velocity (B = 0.282, P < .001) and body weight (B = -0.224, P < .001) were significantly associated with medial elbow torque, but not with the history of medial elbow injuries. CONCLUSIONS: Increased medial elbow torque was associated with greater ball velocity regardless of the history of medial elbow injuries. Youth baseball pitchers with a history of medial elbow injuries within one year had greater medial elbow torque during pitching; however, having a history of medial elbow injuries was not an independent factor in increasing medial elbow torque. Limiting the ball velocity can reduce medial elbow torque and may prevent elbow injuries in youth baseball pitchers. LEVEL OF EVIDENCE: Level II, prospective comparative prognostic investigation with the patients enrolled at different time point.

Gait-related self-efficacy is directly associated with daily step counts in individuals with knee osteoarthritis.

BACKGROUND: In addition to physical factors, psychological factors such as self-efficacy (SE) reportedly affect physical activity (PA) levels in individuals with knee osteoarthritis (OA). However, the relationship between PA and SE for walking tasks in patients with knee OA remains unclear. The present study aimed to investigate the direct and indirect pathways of SE for walking tasks and the influence of previously reported factors on PA level in individuals with knee OA. METHODS: A cross-sectional design was employed. Eighty-five individuals with knee OA were enrolled. The daily step count (Steps) was considered an objective level of PA. The SE for the walking task was assessed using a modified Gait Efficacy Scale (mGES). Data on gait speed (GS), the visual analog scale (VAS) score for knee pain, Kellgren-Lawrence (K-L) grade of radiographic severity of knee OA, age, and body mass index were collected. Path analysis was performed to investigate the direct and indirect effects of these variables on Steps. RESULTS: After exclusion, 70 participants were included. The alternative model, which included Steps, mGES, GS, VAS, K-L grade, and age, showed a good fit. mGES and age had a direct effect on Steps (standardized path coefficients: 0.337 and -0.542, respectively), while the other variables had indirect effects. CONCLUSIONS: The SE for walking tasks was directly associated with Steps representative of the PA level. This finding suggests that SE for the walking task may be important in improving PA levels in individuals with knee OA.

Gait-related Self-efficacy is Low in Older Adults with Knee Osteoarthritis: A Preliminary Study.

OBJECTIVE: To investigate the differences in self-efficacy (SE) for walking tasks between older patients with knee osteoarthritis (OA) and older adults without knee OA. METHODS: A cross-sectional design was employed. Older patients with radiographic knee OA and community-dwelling older adults without knee OA as controls were enrolled in the study. SE for the walking task was assessed using the modified gait efficacy scale (mGES). A Wilcoxon rank-sum test was used to compare the mGES between the groups of participants. A Tobit regression model was used to estimate the difference in mGES. The presence of radiographic knee OA was used as an independent variable. Sex (women), age, and body mass index were used as potential confounding variables in the model. RESULTS: After exclusion, 78 participants (n=40 with knee OA, n=38 controls) were included. The mGES was lower in patients with knee OA than in controls. In the Tobit regression model adjusted for confounding factors, mGES in patients with knee OA was estimated to be 26.8 (95% confidence interval [CI]: 15.8-37.8) points lower than in controls. CONCLUSION: This study demonstrated that mGES was lower in older patients with knee OA than in older adults without knee OA.

High elasticity of the flexor carpi ulnaris and pronator teres muscles is associated with medial elbow injuries in youth baseball players.

OBJECTIVES: The purpose of the present study was to measure the elasticities of the forearm flexor-pronator muscles in youth baseball players and examine their relationships with medial elbow injuries. METHODS: We examined the strain ratios (SR) of the flexor digitorum superficialis (FDS), flexor carpi ulnaris (FCU), and pronator teres (PT) in 89 youth baseball players with medial epicondylar fragmentation (injury group) and in 142 healthy baseball players (control group). An index of muscle elasticity was determined using ultrasound strain elastography. The SR of each muscles was compared between the injury and control groups, and the SR of the both side arms was compared within group. Moreover, multivariable logistic regression analyses were conducted to examine the association of forearm muscle elasticity with medial elbow injuries. RESULTS: The SR of the FCU and PT of the throwing arm were significantly higher in the injury group than in the control group (both P < .001). In the injury group, the SR of the FCU was higher in the throwing arm than in the non-throwing arm (P < .001), but no difference was noted for the PT. Multivariable logistic regression analyses showed that a 0.1 increase of the SR of the FCU of the throwing arm (odds ratio [OR] 1.30, 95% confidence interval [CI] 1.14-1.48) and PT of the throwing arm (OR 1.41, 95% CI 1.19-1.67) and the non-throwing arm (OR 1.31, 95% CI 1.12-1.54) was significantly associated with an increased prevalence of medial elbow injuries. CONCLUSION: High elasticities of the FCU of the throwing arm and PT of both the arms were observed in individuals with medial elbow injuries, and were associated with increased prevalence of medial elbow injuries. These findings may be characteristic of medial elbow injuries in youth baseball players.

Hyperechoic and Low Morphological Changes in the Prefemoral Fat Pad in Individuals with Knee Osteoarthritis Based on Ultrasonographic Findings.

BACKGROUND: To clarify the changes in the echo intensity (EI) in the prefemoral fat pad (PFP) and identify the relationship between the PFP and clinical features of knee osteoarthritis (OA). METHODS: Twenty-six women with knee OA (mean age: 76 years) and 17 healthy women (mean age: 73 years) were enrolled. The Kellgren and Lawrence grading scale was used for the radiographic evaluation of knee OA. The EI of the PFP was measured as grayscale values. The change ratio of the anteroposterior PFP length during quadriceps contraction was measured. Knee range of motion and pain (100-mm visual analog scale) were evaluated. RESULTS: The EI was significantly higher in the OA group than in the healthy group (P < 0.001). The change ratio of the PFP in the OA group was significantly lower than that in the healthy group (P < 0.001). The ranges of knee flexion and extension were correlated with the EI of the PFP (both P < 0.01) and the change ratio of the PFP (both P < 0.01). There was no significant correlation observed with knee pain. CONCLUSION: Hyperechoic changes and a decreased change ratio of the PFP were observed in the patients with knee OA. High EI and decreased morphological PFP changes were associated with decreased ranges of motion.

Effect of heel lifts in elderly individuals with spinal kyphosis.

BACKGROUND: The present study aimed to elucidate the effects of heel lifts on spinal alignment, walking, and foot pressure pattern in elderly individuals with spinal kyphosis. METHODS: The spinal alignment, walking speed, step length and foot pressure of 33 community-dwelling elderly individuals with spinal kyphosis (3 men, 30 women; mean age 77.3 years) were examined before and after the application of 10-mm moderately elastic heel lifts. FINDINGS: Spinal alignment of total inclination (mean value 6.9°vs 4.5°) and thoracic angle (43.6°vs 36.2°) were significantly lower after the application of heel lifts than before the application. The lumbar angle (7.3°vs 10.0°) was significantly higher after the application than before the application. Walking speed (0.78 vs 0.88 m/s) and step length (0.42 m vs 0.45 m) were significantly higher after the application. The partial foot pressure as a percentage of body weight of the hallux (6.7% vs 9.0%) and lateral toes (6.5% vs 9.0%) was significantly higher after the application of heel lifts than before the application. The partial foot pressure as a percentage of body weight of the heel (68.9% vs 57.5%) was significantly lower after the application than before the application. INTERPRETATION: In conclusion, heel lifts influenced the sagittal spinal alignment of elderly individuals. Walking speed and step length increased after the application of these devices. Increase in foot pressure in the hallux and lateral toe areas was probably related to these improvements in walking parameters.

High Thoracic Kyphosis and Backward Trunk Inclination Angles in the Single-Leg Standing Position Associate With Medial Elbow Injuries in Youth Baseball Players: A Cross-Sectional Study.

CONTEXT: Baseball pitching is a coordinated movement involving the spine. A previous study indicated that increased thoracic kyphosis angle in a standing position was a risk factor for medial elbow injuries in youth baseball players. However, spinal alignments in single-leg standing and their relationships with medial elbow injuries, scapular alignment, or hip joint range of motion are unclear. OBJECTIVE: To examine the difference in spinal alignment between standing and single-leg standing positions in youth baseball players and analyze their relationship with elbow injuries, scapular alignment, or hip joint range of motion. DESIGN: Cross-sectional study. SETTING: University laboratory. PARTICIPANTS: There were 51 youth baseball players with medial epicondylar fragmentation (medial elbow injury group) and 102 healthy youth baseball players (control group). MAIN OUTCOME MEASURES: Thoracic kyphosis, lumbar lordosis, and trunk inclination angles during standing and single-leg standing, forward scapular posture, and hip joint range of motion. RESULTS: In the single-leg standing position, the thoracic kyphosis and backward trunk inclination angles were significantly higher in the medial elbow injury group than in the control group (P = .016 and P = .046, respectively). In the standing position, no significant difference was observed between both groups. The thoracic kyphosis angle in single-leg standing was positively correlated with the bilateral forward scapular posture in the medial elbow injury (P = .008 and P < .001 on the throwing and nonthrowing sides, respectively) and control (P = .010 and P = .032 on the throwing and nonthrowing sides, respectively) groups. CONCLUSIONS: High thoracic kyphosis and backward trunk inclination angles are characteristics during single-leg standing in youth baseball players with medial elbow injuries. Spinal alignment measurement in single-leg standing may be useful for identifying youth baseball players who are at risk for sustaining medial elbow injury.

Diaphragm thickening assessed by ultrasonography is lower than healthy adults in patients with chronic obstructive pulmonary disease.

BACKGROUND: Ultrasound imaging has been widely used for imaging of the diaphragm thickness (Tdi) and thickening. Few studies assessed the Tdi using ultrasonography in patients with chronic obstructive pulmonary disease (COPD). We measured the Tdi and thickening in patients with COPD compared with healthy younger and healthy older adults to reveal the influence of ageing and/or COPD. METHODS: Thirty-eight male patients with COPD (age 72 ± 8 years), 15 healthy younger (age 22 ± 1 years) and 15 healthy older (age 72 ± 5 years) male volunteers were recruited. We measured Tdi at total lung capacity (TdiTLC ), functional residual capacity (TdiFRC ) and residual volume (TdiRV ) using B-mode ultrasonography. We calculated the change ratio of TdiTLC and TdiRV (ΔTdi%). We used a one-way analysis of variance and multiple comparison test for the comparison analysis. RESULTS: The TdiTLC and the ΔTdi% were significantly lower in patients with COPD compared to the healthy adults. There was no significant difference in these values with age. There was no between group difference in the TdiFRC or TdiRV . CONCLUSIONS: Our results indicate significant differences in TdiTLC and ΔTdi% between patients with COPD and healthy adults. Therefore, diaphragm ultrasonography can assess diaphragm dysfunction associated with COPD. We suggest that it is better to use TdiTLC and ΔTdi% (not only Tdi at rest) to assess diaphragm function.

Gait characteristics and their associations with clinical outcomes in patients with chronic obstructive pulmonary disease.

BACKGROUND: Abnormalities of spatiotemporal gait parameters are frequently observed in chronic obstructive pulmonary disease (COPD). However, associations of gait parameters with clinical outcomes and their implementation into clinical practice have not been established. RESEARCH QUESTION: To investigate gait abnormalities and their association with clinical outcomes of COPD. METHODS: This study included 34 male outpatients with COPD and 16 community-dwelling healthy men aged ≥65 years. The subjects underwent a ten-metre walk test wearing an accelerometer. Data on gait speed, step length, cadence, walk ratio, acceleration magnitude, and standard deviation of step time (step time SD) were collected. Forced expiratory volume in 1-second, modified Medical Research Council dyspnoea score, six-minute walk distance (6MWD), quadriceps muscle strength (QMVC), and physical activity (daily steps and time spent in moderate to vigorous physical activity per day) were measured in the COPD group as clinical outcomes of COPD. We tested group differences in gait parameters, associations between gait parameters and COPD clinical outcomes, and predictive capability of gait parameters for reductions in 6MWD, QMVC, and daily steps in COPD. RESULTS: All gait parameters except walk ratio deteriorated in COPD. Step time SD and gait speed were significant independent predictors of 6MWD in COPD (B=-0.440, p = 0.001, B = 0.339, p = 0.007, respectively). Step length was a significant independent predictor of QMVC (B=-0.609, p < 0.001) and daily steps (B=-0.453, p = 0.006). Step length was a significant predictor of muscle weakness and physical inactivity, and step time SD was significant in predicting poor 6MWD in COPD. SIGNIFICANCE: Significant associations between gait abnormalities measured by an accelerometer and deficits in extra-pulmonary features of COPD were observed. An accelerometer-based gait analysis could be an alternative approach to assessing gait abnormalities and screening of functional decline in COPD.

In Vivo Flattening of the Central Aponeurosis of the Rectus Femoris Due to Knee Extension Torque in Healthy Young and Elderly Individuals With Knee Osteoarthritis.

ABSTRACT: We aimed to elucidate the relationship between active force production and the curvature of the central aponeurosis (CA) of the rectus femoris in young healthy participants as fundamental data and compare the muscle CA curvature before and after straight leg raising (SLR) training in participants with knee osteoarthritis (OA). Central aponeurosis curvature was determined during submaximal and maximal voluntary contractions (MVCs) using ultrasonography. Twenty-five young healthy female volunteers underwent ultrasonographic measurements under conditions of isometric MVC. They were divided into a flat shaped CA group (flat) and an incompletely flat shaped CA group (remnant). Central aponeurosis curvature was calculated as the ratio of CA height and length in the axial view. Central aponeurosis shape and muscular strength before and after muscle training were measured in 11 participants with knee OA. In the young healthy individuals, maximal voluntary torque and changes in CA curvature were significantly higher in the flat group than in the remnant group (2.15 Nm/kg and - 17.7% vs 1.75 Nm/kg and -9.8%, respectively; P = 0.005). The rate of change of the CA curvature during contraction was significantly correlated with maximal voluntary torque corrected for body mass (r = 0.512). The CA curvature progressively decreased as %MVC increased. In the OA group, CA curvature during MVC after SLR training was significantly lower than that before SLR training (3.2% vs 7.2%; P = 0.031). Central aponeurosis curvature was associated with muscle strength, and the results supported our hypothesis that geometric observation of CA changes during contractions may reflect muscle fiber function. We aim to develop a new ultrasonographic skeletal muscle evaluation method based on our present findings.

Ultrasonographic Morphological Changes in the Prefemoral Fat Pad Associated with Knee Osteoarthritis.

BACKGROUND: In normal knees, quadriceps contraction changes the shape of the prefemoral fat pad (PFP). However, in persons with knee osteoarthritis (OA), the functional or morphological changes of the PFP are unclear. This study aimed to clarify the morphological changes in the PFP in individuals with knee OA through ultrasonography. MATERIALS AND METHODS: Participants were divided into the OA (36 knees; mean age, 74 years), elderly (31 knees; mean age, 70 years), and young (26 knees; mean age, 21 years) groups. The anteroposterior (AP) length of the PFP before and during isometric quadriceps contraction at 0°, 30°, 60°, and 90° knee flexion was measured ultrasonographically. The difference between the maximum and minimum length values, change in length, was also measured. These parameters were compared among the three groups. In the OA group, correlations between the parameters and clinical features (knee pain; visual analog scale, knee range of motion [ROM], Kellgren and Lawrence (K/L) grade, and intercondylar distance) were examined by Spearman and Pearson's correlation coefficient tests. RESULTS: The AP lengths of the PFP before contraction were significantly lower in the OA group than in elderly group and young group at 30° (6.9 ± 2.5 vs. 12.0 ± 3.6 or 11.1 ± 2.7 mm, respectively; in order P = 0.014, P = 0.006) and 60° (6.5 ± 2.0 vs. 9.7 ± 2.5 or 9.1 ± 2.7 mm, respectively; both P < 0.001). The AP lengths of the PFP during contraction were significantly lower in the OA group than in elderly group and young group at 0° (6.7 ± 2.3 vs. 8.8 ± 3.7 or 9.1 ± 1.6 mm, respectively; both P < 0.001), 30° (7.9 ± 2.6 vs. 12.9 ± 3.7 or 13.0 ± 2.6 mm, respectively; both P < 0.001), and 60° (7.1 ± 2.5 vs. 13.5 ± 2.6 or 13.6 ± 3.0 mm, respectively; both P < 0.001). The change in length before maximum isometric quadriceps contraction was significantly lower in the knee OA group than in both elderly and young groups (3.3 ± 1.9 vs. 8.4 ± 2.5 or 6.8 ± 3.0 mm, respectively; both P < 0.001). The change in length during contraction was also significantly lower in the knee OA group than in both the elderly and young groups (3.9 ± 2.3 vs. 8.7 ± 2.3 or 8.9 ± 2.0 mm, respectively; both P < 0.001). In the OA group, change in length during contraction was significantly associated with knee pain (r = -0.476, P = 0.007), knee ROM (r = 0.388, P = 0.019), and Kellgren and Lawrence grade (r = -0.357, P = 0.045). CONCLUSIONS: In knee OA, movement of PFP was decreased more than healthy participants. In the knee OA group, the decrease of the morphological change of the PFP showed the relationship between VAS score, knee extension ROM, intercondylar distance (ICD), and K/L grade. An evaluation to the PFP may be required in individuals with knee OA.

Relationship between balance and physical activity measured by an activity monitor in elderly COPD patients.

BACKGROUND: Little is known regarding the relationship between balance impairments and physical activity in COPD. There has been no study investigating the relationship between balance and objectively measured physical activity. Here we investigated the association between balance and physical activity measured by an activity monitor in elderly COPD patients. MATERIALS AND METHODS: Twenty-two outpatients with COPD (mean age, 72±7 years; forced expiratory volume in 1 second, 53%±21% predicted) and 13 age-matched healthy control subjects (mean age, 72±6 years) participated in the study. We assessed all 35 subjects' balance (one-leg standing test [OLST] times, Short Physical Performance Battery total scores, standing balance test scores, 4 m gait speed, and five-times sit-to-stand test [5STST]) and physical activity (daily steps and time spent in moderate-to-vigorous physical activity per day [MV-PA]). Possible confounders were assessed in the COPD group. The between-group differences in balance test scores and physical activity were analyzed. A correlation analysis and multivariate regression analysis were conducted in the COPD group. RESULTS: The COPD patients exhibited significant reductions in OLST times (P=0.033), Short Physical Performance Battery scores (P=0.013), 4 m gait speed (P<0.001), five-times sit-to-stand times (P=0.002), daily steps (P=0.003), and MV-PA (P=0.022) compared to the controls; the exception was the standing balance test scores. The correlation and multivariate regression analyses revealed significant independent associations between OLST times and daily steps (P<0.001) and between OLST times and MV-PA (P=0.014) in the COPD group after adjusting for possible confounding factors. CONCLUSION: Impairments in balance and reductions in physical activity were observed in the COPD group. Deficits in balance are independently associated with physical inactivity.

Ultrasonographic Morphologic Changes of the Central Aponeurosis of the Rectus Femoris Muscle in Individuals With Knee Osteoarthritis.

The aim of this study was to clarify the morphologic characteristics of central aponeurosis (CA) of the rectus femoris (RF) muscle in individuals with medial knee osteoarthritis (OA). Forty legs in 26 individuals with medial knee OA (OA group), 41 legs in 21 elderly individuals (elderly group), and 40 legs in 20 young individuals (young group) were investigated. We measured the following 4 parameters: (1) ratio of CA length, expressed as the percentage of RF length; (2) CA morphologic type (curved, straight, S-shaped, or irregular); (3) CA direction, defined as the direction of the line from the anterior to posterior ends of the CA (lateral or medial); and (4) intercondylar distance (ICD). Ratio of CA length in the OA group was significantly smaller than that in the other 2 groups. The curved CA type was significantly more frequent in the young group than in the other 2 groups. The irregular type was observed in only 7 legs in the OA group. In the young group, CA direction was classified as medial in all cases. Laterally directed CA was observed only in the OA and elderly groups. Within the OA group, ICD in laterally directed CA was significantly larger than that in medially directed CA. Central aponeurosis observed in the RF muscle in individuals with medial knee OA is shorter and sometimes shows an irregular shape. Laterally directed CA is associated with increased ICD in knee OA. Attention should be given to the tendon-aponeurosis complex in individuals with medial knee OA.

The Dmrt1 expression in sex-reversed gonads of amphibians.

Gonadal differentiation in amphibians is sensitive to steroids. The phenotypic sex can be changed by hormonal treatments, but the molecular mechanism for gonadal differentiation is not known. Up to date, many genes involved in gonadal differentiation have been isolated in vertebrates. Dmrt1, a gene that contains the DM-domain (Doublesex/Mab-3 DNA-binding motif), is considered to be one of the essential genes involved in the testicular differentiation cascade in mammals, birds, reptiles, and fish. However, this gene has not been isolated in amphibians yet. To elucidate its role(s) for gonadal differentiation in vertebrates, a molecular cloning of Dmrt1 in amphibians is urgent. In this study, we have successfully isolated a Dmrt1 homolog from the frog Rana rugosa testes cDNA library and examined its expression during gonadal differentiation and in sex-reversed gonads. The Dmrt1 mRNA was exclusively detected in testis among adult tissues by the RT-PCR analysis. The Dmrt1 was first expressed in the differentiating testis at stage XXV in which spermatogonia are only germ cells, and became stronger at later stages. Moreover, the Dmrt1 transcript was not detected during ovarian differentiation. However, this gene was clearly expressed in XX sex-reversed gonads caused by injection of testosterone into all-female tadpoles that have well-differentiated ovaries. Taken together, the results suggest that Dmrt1 is closely implicated in testicular, but not ovarian differentiation in amphibians.