Reliability and validity of velocity measures and regression methods to predict maximal strength ability in the back-squat using a novel linear position transducer

The purpose of this study was to examine the reliability of load-velocity profiles (LVPs) and validity of 1-repetition maximum (1-RM) prediction methods in the back-squat using the novel Vitruve linear position transducer (LPT). Twenty-five men completed a back-squat 1-RM assessment followed by 2 LVP trials using five incremental loads (20%–40%–60%–80%–90% 1-RM). Mean propulsive velocity (MPV), mean velocity (MV) and peak velocity (PV) were measured via a (LPT). Linear and polynomial regression models were applied to the data. The reliability and validity criteria were defined a priori as intraclass correlation coefficient (ICC) or Pearson correlation coefficient (r) . 0.70, coefficient of variation (CV) 410%, and effect size (ES) \0.60. Bland Altman analysis and heteroscedasticity of errors (r2) were also assessed. The main findings indicated MPV, MV and PV were reliable across 20%–90% 1-RM (CV \ 8.8%). The secondary findings inferred all prediction models had acceptable reliability (CV \ 8.0%). While the MPV linear and MV linear models demonstrated the best estimation of 1-RM (CV \ 5.9%), all prediction models displayed unacceptable validity and a tendency to overestimate or underestimate 1-RM. Mean systematic bias (27.29 to 2.83 kg) was detected for all prediction models, along with little to no heteroscedasticity of errors for linear (r2 \ 0.04) and polynomial models (r2 \ 0.08). Furthermore, all 1-RM estimations were significantly different from each other (p \ 0.03). Concludingly, MPV, MV and PV can provide reliable LVPs and repeatable 1-RM predictions. However, prediction methods may not be sensitive enough to replace direct assessment of 1-RM. Polynomial regression is not suitable for 1-RM prediction

Reliability of the Coach’s Eye Goniometer Application during Squat Exercise

This study examined the test re-test, intrarater and interrater reliability of joint kinematics from the Coach’s Eye smartphone application. Twenty-two males completed a 1-repetition maximum (1-RM) assessment followed by 2 identical sessions using 5 incremental loads (20%-40%-60%-80%-90% 1-RM). Peak flexion angles at the hip, knee, and ankle joints were assessed using 1 experienced practitioner and 1 inexperienced practitioner. The acceptable reliability thresholds were defined as intraclass correlation coefficient (ICC) (r) > 0.70 and coefficient of variation (CV) ≤ 10%. The test re-test reliability of peak hip and knee flexion were reliable across 20-90% 1-RM (r > 0.64; CV 0.70; CV 0.11). The intrarater reliability was near perfect (r > 0.90) except for peak ankle flexion (r > 0.85). The interrater reliability was nearly perfect (r > 0.91) except for hip flexion at 80% 1-RM and ankle flexion at 20% (r > 0.77). Concludingly, the Coach’s Eye application can produce repeatable assessments of joint kinematics using either a single examiner or 2 examiners, regardless of experience level. The Coach’s Eye can accurately monitor squat depth

A Unique Combination of Male Germ Cell miRNAs Coordinates Gonocyte Differentiation

The last 100 years have seen a concerning decline in male reproductive health associated with decreased sperm production, sperm function and male fertility. Concomitantly, the incidence of defects in reproductive development, such as undescended testes, hypospadias and testicular cancer has increased. Indeed testicular cancer is now recognised as the most common malignancy in young men. Such cancers develop from the pre-invasive lesion Carcinoma in Situ (CIS), a dysfunctional precursor germ cell or gonocyte which has failed to successfully differentiate into a spermatogonium. It is therefore essential to understand the cellular transition from gonocytes to spermatogonia, in order to gain a better understanding of the aetiology of testicular germ cell tumours. MicroRNA (miRNA) are important regulators of gene expression in differentiation and development and thus highly likely to play a role in the differentiation of gonocytes. In this study we have examined the miRNA profiles of highly enriched populations of gonocytes and spermatogonia, using microarray technology. We identified seven differentially expressed miRNAs between gonocytes and spermatogonia (down-regulated: miR-293, 291a-5p, 290-5p and 294*, up-regulated: miR-136, 743a and 463*). Target prediction software identified many potential targets of several differentially expressed miRNA implicated in germ cell development, including members of the PTEN, and Wnt signalling pathways. These targets converge on the key downstream cell cycle regulator Cyclin D1, indicating that a unique combination of male germ cell miRNAs coordinate the differentiation and maintenance of pluripotency in germ cells

Neuromuscular predictors of competition performance in advanced international female weightlifters: A cross-sectional and longitudinal analysis

The aim of this study was to investigate the physical determinants of weightlifting competition performance based on Isometric Mid-Thigh Pull (IMTP) and Countermovement Jump (CMJ) force-time variables, in a cross-sectional and longitudinal analysis. Ten British advanced international female weightlifters’ (age 23.4 ± 3.3 years, height 1.59 ± 0.06m, body mass 63.3 ± 8.82kg, training history 6.1 ± 3.2 years) competition results and neuromuscular assessment data collected as part of the British Weight Lifting World Class Programme were utilised for the purpose of this study. All data were averaged for two consecutive 1-year periods. The cross-sectional analysis utilised the second year of data, whereas the longitudinal analysis assessed the mean change between the two years. The cross-sectional analysis results reveal IMTP Net Isometric Peak Force (PF) and CMJ Peak Power (PP) predict 94.2%, 95.1% and 91.8% of the variance in Total, Snatch and Clean & Jerk competition performance respectively (p = <0.005). The longitudinal analysis results revealed that ∆IMTP PF was the only predicting factor of longitudinal change in weightlifting competition performance predicting 41.5%, 41.7% and 42.5% of ∆Total, ∆Snatch and ∆Clean & Jerk respectively (p = <0.005). The assessments and equations may be utilised by coaches or sports scientists to inform the prescription of training and help predict competition performance

Maximal isometric force in the start of the first pull exhibits greater correlations with weightlifting performance than in the mid-thigh position in national and international weightlifters

This investigation compared the maximal isometric force capacity between the start position of the first pull (IPSP) and isometric mid-thigh pull (IMTP), and their relationship with weightlifting competition performance in twenty national and international, male and female weightlifters. Isometric strength assessment and competition performance data collected as part of the routine sport science services of a national weightlifting performance programme were used for this study. Differences in isometric peak force (PkF) and allometrically scaled peak force (PkFa) between the IPSP and IMTP were evaluated using a paired-samples t-test. The relationships between absolute and allometrically scaled IPSP, IMTP, Total (TOT), Snatch (SN) and Clean & Jerk (CJ) variables were analysed using Pearson's Product-Moment Correlation. Fisher's r-to-z transformation was used to statistically compare the correlation values between the IPSP and IMTP with weightlifting performance measures. The IMTP PkF and PkFa were significantly greater than the IPSP PkF and PkFa, respectively, across combined (COM), male (M) and female (F) groups (p = < 0.001). However, the IPSP PkF exhibited significantly greater correlations with SN (r = 0.94 vs. 0.83, p < 0.05) and TOT (r = 0.95 vs. 0.86, p < 0.05) than the IMTP PkF in the COM group. In addition, the IPSP PkFa exhibited a significantly greater correlation with allometrically scaled snatch (SNa) (r = 0.83 vs. 0.51, p < 0.05) than the IMTP PkFa in the COM group. No significant correlations were observed between the IPSP PkFa and IMTP PkFa across M, F and COM groups. These findings suggest that the maximal force capacity in the IPSP is a greater determinant of weightlifting performance than in the IMTP, however, each may be representative of independent neuromuscular qualities. Coaches and practitioners working with weightlifters may consider implementing the IPSP assessment in addition to the IMTP to evaluate the strength characteristics specific to the different phases of the pull