Takashi Nagai

Background/Objectives: Three-dimensional motion analysis is often used to evaluate improvements or decrements in movement patterns in athletes. The purpose of this study was to evaluate the reliability of joint flexion/extension angles of the pitching elbow and bilateral knees and hips in softball pitchers. Methods: Fourteen softball pitchers (17.9 ± 2.3 years) were tested in one session consisting of four sets of five consecutive fastballs and a second session of two sets of five fastballs. The magnitude of systematic bias and within-subject variation was calculated between pitches. An iterative intraclass correlation coefficient (ICC) process was used to determine intra- and inter-session reliability, standard error of measurement and minimal detectable change. Results: Reductions in within-subject variation were observed for all variables when the number of pitches used in calculations was increased. Intra-session ICC values ranged from an average of 0.643 for pitching elbow to 0.989 for stride leg knee. Inter-session ICC values ranged from an average of 0.663 for pitching elbow to 0.996 for stride leg knee. Conclusions: Joint flexion/extension angles during the softball windmill pitch can be measured with good to high reliability using three-dimensional motion analysis. Biomechanical analysis can be confidently used to detect changes in the pitching motion over the course of a season or following an intervention.

Introduction: It is well documented that marked weakness of the quadriceps is present after knee joint injury. This joint trauma induces a presynaptic reflex inhibition of musculature surrounding the joint, termed arthrogenic muscle inhibition (AMI). The extent to which anterior cruciate ligament (ACL) injury affects thigh musculature motor unit activity, which may affect restoration of thigh muscle strength after injury, is undetermined.Methods: A randomized protocol of knee flexion and extension isometric contractions (10%–50% maximal voluntary isometric contraction) were performed for each leg on 54 subjects with electromyography array electrodes placed on the vastus medialis, vastus lateralis, semitendinosus, and biceps femoris. Longitudinal assessments for motor unit recruitment and average firing rate were acquired at 6-month intervals for 1 year post ACL injury.Results: The ACL-injured population demonstrated smaller quadriceps and hamstrings motor unit size (assessed via motor unit action potential peak-to-peak amplitude) and altered firing rate activity in both injured and uninjured limbs compared to healthy controls. Motor unit activity remained altered compared to healthy controls at 12 months post ACL reconstruction (ACLR).Discussion: Motor unit activity was altered after ACLR up to 12 months post-surgery. Further research is warranted to optimize rehabilitation interventions that adequately address altered motor unit activity and improve safety and success with return to sport after ACLR. In the interim, evidence based clinical reasoning with a focus on development of muscular strength and power capacity should be the impetus behind rehabilitation programming to address motor control deficits.

A mode-specific swimming protocol to assess maximal aerobic uptake (VO₂max_sw) is vital to accurately evaluate swimming performance. A need exists for reliable and valid swimming protocols that assess VO₂max_sw in a flume environment. The purpose was to assess: (a) reliability and (b) “performance” validity of a VO₂max_sw flume protocol using the 457-m freestyle pool performance swim (PS) test as the criterion. Nineteen males (n = 9) and females (n = 10) (age, 28.5 ± 8.3 years.; height, 174.7 ± 8.2 cm; mass, 72.9 ± 12.5 kg; %body fat, 21.4 ± 5.9) performed two flume VO₂max_sw tests (VO₂max_swA and VO₂max_swB) and one PS test [457 m (469.4 ± 94.7 s)]. For test–retest reliability (Trials A vs. B), moderately strong relationships were established for VO₂max_sw (mL·kg⁻¹·min⁻¹)(r= 0.628, p = 0.002), O₂pulse (mL O₂·beat⁻¹)(r = 0.502, p = 0.014), VEmax (L·min⁻¹) (r = 0.671, p = 0.001), final test time (sec) (0.608, p = 0.004), and immediate post-test blood lactate (IPE (BLa)) (0.716, p = 0.001). For performance validity, moderately strong relationships (p < 0.05) were found between VO₂max_swA (r =−0.648, p = 0.005), O₂pulse (r= −0.623, p = 0.008), VEmax (r = −0.509 p = 0.037), and 457-m swim times. The swimming flume protocol examined is a reliable and valid assessment of VO₂max_sw., and offers an alternative for military, open water, or those seeking complementary forms of training to improve swimming performance.

Consistent differences between males and females have been shown in land-based measurements of anaerobic power and capacity. However, these differences have not been investigated for a tethered 30-s maximal swimming test (TST). The purpose of this study is to explore gender differences in land and pool-based assessments of anaerobic power (F_peak) and capacity (F_mean), as well as the influence of body composition. Thirteen males and fifteen females completed land (Wingate (WAnT)) and pool-based (TST) measures of anaerobic power and capacity previously described in the literature. Additionally, the subjects completed assessments of body composition via air displacement plethysmography. The males produced higher force than the females for F_peak (p < 0.001) and F_mean (p = 0.008) during the TST. However, linear regression analysis determined that lean mass significantly predicted F_peak (p = 0.002) and F_mean (p < 0.001) during the TST, while gender was no longer significant (p = 0.694 and p = 0.136, respectively). In conclusion, increases in anaerobic power and capacity (F_peak and F_mean) may be a function of increased lean mass in males and females, warranting future research on the impact of resistance training programs on force production and swimming performance.

Joint trauma induces a presynaptic reflex inhibition termed arthrogenic muscle inhibition (AMI) that prevents complete activation of muscles. Reduced motor unit (MU) output is a hypothesised mechanism for persistent strength deficits. The objective of this study was to determine MU characteristics of thigh musculature and determine how they change with anterior cruciate ligament (ACL) injury compared to healthy controls. A randomised protocol of knee flexion/extension isometric contractions (10–50% maximal voluntary isometric contraction) was performed for each leg with surface EMG 5‐pin array electrodes placed on the vastus medialis, vastus lateralis, semitendinosus and biceps femoris. Longitudinal assessments for average rate coding, recruitment thresholds and MU action potentials were acquired at 6‐month intervals. With exception of the vastus medialis, all thigh musculature of ACL‐injured demonstrated smaller MU action potential peak‐to‐peak amplitude. For average rate coding, ACL‐injured demonstrated lower coding rates than Controls for the quadriceps (p < .05) and higher rates than Controls for the hamstrings (p < .05). These MU characteristics were different from Controls after ACL reconstruction up to 12 months post‐surgery, yet maximal strength increased during this time frame. As thigh MU characteristics are known across phases of ACL rehabilitation, future studies can assess these patterns of motor control and their potential to determine risk of re‐injury. Further, future rehabilitation can target specific intervention programmes to restore motor control.Highlights Motor unit strategies of arthrogenic muscle inhibition are characterised for the first time via decomposed EMG. Motor unit deficits of thigh musculature persist throughout all phases of ACL rehabilitation, even after return‐to‐sport. After ACL injury, motor unit sizes at similar recruitment thresholds were smaller than those of healthy controls.

Background: Eccentric hamstring strength and hamstring/quadriceps strength ratios have been identified as modifiable risk factors of hamstring strains. Additionally, those strength and flexibility characteristics are commonly used as clinical tests to monitor progress of athletes with acute or chronic hamstring strains. Although hamstring strains are common among basketball athletes, normative values of knee strength and flexibility characteristics are scarce. Normative values for these athletes would be important in prevention and management of hamstring strains. Purpose: To establish quadriceps and hamstring isokinetic strength and flexibility values among high school basketball athletes and examine the effects of sex and age. Study Design: Cross-sectional research Methods: Isokinetic knee muscular strength (concentric quadriceps [QuadC], concentric hamstring [HamC], eccentric hamstring [HamE], and strength ratios ([HamC/QuadC and HamE/Quad]), flexibility of hip flexors and quadriceps during a Modified Thomas test, and flexibility of hip extensors and hamstring during passive straight leg raise (SLR) and passive knee extension (PKE) tests were measured. Effects of sex and age were analyzed using t-tests and analysis of variance, respectively with Bonferroni corrected post hoc tests (p≤0.01). Results: A total of 172 high school basketball athletes (64 males/108 females; mean age (range): 15.7 (14-18) years old) participated in the study. Male athletes were significantly stronger than female athletes (QuadC: ppp=0.759-0.816; HamE/QuadC: p=0.022-0.061). Among male athletes, a significant effect of age on quadriceps and hamstring strength was observed: older male athletes were stronger than younger male athletes. Contrarily, there were no effects of age on strength among female athletes. There were significant sex differences in quadriceps flexibility, SLR, and PKE (female athletes were more flexible; p=0.001-0.005) while no sex differences were found in hip flexor flexibility (p=0.105-0.164). There were no effects of age for any flexibility variables within male and female athletes (p=0.151-0.984). Conclusion: The current results provide normative values for hamstring strength and flexibility in high school basketball athletes. These normative values may further assist sports medicine specialists to develop screening tests, interventions, and return-to-sport criteria in this population. Level of Evidence: 3B

Winters, JD, Heebner, NR, Johnson, AK, Poploski, KM, Royer, SD, Nagai, T, Randall, CA, Abt, JP, and Lephart, SM. Altered physical performance following advanced special operations tactical training. J Strength Cond Res 35(7): 1809–1816, 2021—The purpose of this study was to determine how the unique challenges of specific military tactical training phases influence overall physical performance characteristics. Broad jump, 5-10-5, 300-yd shuttle, percent body fat (%BF), anaerobic power (AP) and anaerobic capacity (AC), maximal oxygen uptake (V̇o ₂max), isokinetic knee extension/flexion strength, shoulder internal/external rotation strength, and trunk extension/flexion strength were collected on 73 United States Marine Corps Forces Special Operations Command (MARSOC) students (age: 27.4 ± 3.8 years, height: 178.7 ± 6.6 cm, and body mass: 85.8 ± 9.4 kg) at the beginning of (P1), in between (P2), and at the completion of 2 distinct tactical training phases (P3). Linear mixed models were used to analyze within-subject performance changes over the 3 time points, and post hoc Bonferroni pairwise comparisons analyzed performance changes between each testing time point. There were significant changes in broad jump (p < 0.0001), 5-10-5 agility time (p < 0.001), %BF (p = 0.011), AP (p < 0.0001), V̇o ₂max (p = 0.001), and both right and left shoulder internal rotation strength (p = 0.004 and p = 0.015, respectively) between P1 and P2. There were also significant changes in 300-yd shuttle run time (p = 0.001), AP (p < 0.0001), AC (p < 0.0001), left knee extension strength (p = 0.006), trunk flexion strength (p < 0.0001), and left shoulder external rotation strength (0.027) between P2 and P3. Identifying the effect that specific tactical training phases may have on physical performance will allow for the development of effective phase-specific evidence-based human performance programs, reducing performance deficits and thereby reducing the risk of injury.

Weaker hamstrings muscular forces and lower ratio of the hamstrings/quadriceps muscular forces in female athletes have been identified as modifiable risk factors for anterior cruciate ligament (ACL) injuries. However, sex differences in athletes’ ability to react to visual cues (Choice Visual‐Motor Reaction Time: VMRT) and to generate knee muscular forces (rate of force development: RFD) immediately following the visual cues were largely unknown. Therefore, the purpose of the study was to examine sex differences in Choice VMRT and RFD. A total of 50 high school basketball athletes (26F/24 M) participated in the study. Subjects sat in the knee dynamometer chair with their knee secured at 70° of knee flexion and performed knee extension or flexion maximum voluntary isometric contractions immediately after they saw the visual cue: “UP” or “DOWN” arrows, respectively. Choice VMRT was defined as the time between the visual cue and the initiation of muscular force development (>5Newtons). RFD was calculated by dividing the changes in forces over the changes in time at four time points (0–50/100/150/200 ms). Peak muscular forces and RFD were normalized to their body mass. Average of three trials in each direction (flexion and extension) in each leg was used for statistical analyses. Females had significantly slower Choice VMRT (p < 0.001–0.027) and lower knee extension RFD at 100 ms (p = 0.005). In addition, females had significantly higher knee flexion/extension ratio than males in late RFD (150 ms and 200 ms) (p < 0.004). The current study has provided additional sensorimotor characteristics of athletes and sexes in addition to their knee muscular characteristics.

Nagle Zera, J, Nagle, EF, Nagai, T, Lovalekar, M, Abt, JP, and Lephart, SM. Tethered swimming test: reliability and the association with swimming performance and land-based anaerobic performance. J Strength Cond Res 35(1): 212–220, 2021—The purpose of this study was 3-fold: (a) to examine the test-retest reliability of a 30-second maximal tethered freestyle swimming test (TST), (b) to assess the validity of the TST by examining the association with sprint swimming performance, and (c) to examine the associations between a swim-specific and land-based measure of anaerobic performance. A total of 29 male and female swimmers were recruited to participate in the study. Each subject completed a Wingate Anaerobic cycling test (WAnT), 2 or 4 TST, and a 22.9 m (25 yd), 45.7 m (50 yd), and 91.4 m (100 yd) maximal freestyle performance swims (PS). Mean and peak force (F _mean and F _peak) were recorded for both the WAnT and TST, and average swimming velocity and time were recorded for the PS. In addition, physiological and perceptual measures were recorded immediately postexercise for all tests. The results of the present investigation showed strong intersession and intrasession reliability (R = 0.821–0.975; p < 0.001) for force parameters of the TST. Moderate correlations were found between F _mean and PS time and velocity of all distances, with slightly weaker correlations between F _peak and the 22.9 m (time and velocity) and 45.7 m (velocity) PS. Finally, moderate correlations were found for F _mean and F _peak of the TST and WAnT. This study demonstrated that the TST is a reliable measure, with moderate association with swimming performance, producing similar physiological responses compared with free swimming. Therefore, future research should focus on investigating the potential benefits of using the TST as a regular assessment tool as a part of a competitive swimming training program to track adaptations and inform training decisions.