Isometric Mid-thigh Pull Kinetics: Sex Differences and Response to Whole-Body Vibration

Upper body push to pull ratios in law enforcement officer recruits

BACKGROUND: Law enforcement recruits (LER) often encounter shoulder injuries, which may cause attrition from academies. Investigating required upper body muscular fitness may inform of muscular balance around shoulder joints through anterior and posterior ratios in LER. OBJECTIVE: To investigate push to pull ratios (P2P) and factors related with P2P in LER. METHODS: LER (95 males; 12 females) completed testing during a single session in the academy’s first week: body mass, one-repetition maximum (1RM) bench press, push-up repetitions (reps) to failure, and pull-up reps to failure. Calculations were: estimated pull-up 1-RM=body mass+0.033*(body mass x pull-ups); endurance P2P (eP2P)=push-ups / pull-ups; strength P2P (sP2P)=bench press 1RM / estimated pull-up 1-RM. Pearson correlation coefficients assessed relationships among tests and P2P (p <  0.05). RESULTS: The sP2P was positively correlated with bench press 1-RM and push-ups. The eP2P was negatively associated with pull-up reps and 1-RM. Females had similar eP2P, but lower sP2P than male recruits (p <  0.05). CONCLUSION: Practitioners may benefit from examining eP2P and sP2P as they should not be used interchangeably. Future research should examine whether the P2P ratios are associated with injury and subsequent inability to successfully complete law enforcement training academies.

Do baseline physical fitness measures predict law enforcement academy graduation?

BACKGROUND: Law enforcement officers experience high stress levels and perform various physical tasks. Thus, law enforcement academies emphasize physical fitness training and assessment. OBJECTIVE: To examine fitness test-performances and determine which entry-level fitness components best predict likelihood of successful law enforcement academy graduation. METHODS: Recruits (151 males, 42 females) completed initial academy fitness testing: one-repetition maximum bench press, push-ups, sit-ups, pull-ups, sit-and-reach, 1.5-mile run, and work performance test. Chi-square and t-tests were used to examine gender differences. Correlation coefficients assessed relationships, while logistical regression determined the best fitness components for predicting graduation (p < 0.05). RESULTS: Males had greater fitness performances except pull-ups, sit-ups and sit and reach (p < 0.05). Distributions of below average fitness performances were similar between genders with majority of recruits performing below average on all tests. Gender, age, push-ups, and pull-ups explained 18% of the variance in graduation rates (p < 0.05). Males were 4.68 (p < 0.05) times more likely to graduate, but other predictors were not significant. CONCLUSIONS: No single fitness test predicted the likelihood of graduation and majority of performances were below average, suggesting the importance for proficiency across multiple fitness components. Considering lower fitness performances and graduation rates, females may further benefit from training programs prior to academy entrance.

Relationship Between Isokinetic Lower-Limb Joint Strength, Isometric Time Force Characteristics, and Leg-Spring Stiffness in Recreational Runners

Neuromuscular characteristics, such as lower-limb joint strength and the ability to rapidly generate force, may play an important role in leg-spring stiffness regulation. This study aimed to investigate the relationship between isokinetic knee and ankle joint peak torque (PT), the force-time characteristics of isometric mid-thigh pull (IMTP), and leg stiffness (K_leg)/vertical stiffness (K_vert) in recreationally trained runners. Thirty-one male runners were recruited and underwent three separate tests. In the first session, the body composition, K_leg, and K_vert at running speeds of 12 and 14 km⋅h^–1 were measured. In the second session, isokinetic knee and ankle joint PT at 60°⋅s^–1 were tested. The force-time characteristics of the IMTP were evaluated in the final session. Pearson’s product-moment correlations, with the Benjamini–Hochberg correction procedure, showed that the knee flexor concentric and eccentric and extensor concentric PT (r = 0.473–0.654, p < 0.05) were moderate to largely correlated with K_leg and K_vert at 12 and 14 km⋅h^–1. The knee extensor eccentric PT (r = 0.440, p = 0.050) was moderately correlated with the 14 km⋅h^–1K_vert. The ankle plantar flexor concentric and dorsiflexor eccentric PT (r = 0.506–0.571, p < 0.05) were largely correlated with K_leg at 12 km⋅h^–1. The ankle plantar flexor concentric and eccentric and dorsiflexor eccentric PT (r = 0.436–0.561, p < 0.05) were moderate to largely correlated with K_vert at 12 and 14 km⋅h^–1. For IMTP testing, high correlation was only found between the IMPT peak force (PF) and K_vert at 14 km⋅h^–1 (r = 0.510, p = 0.014). Thus, superior leg-spring stiffness in recreational runners may be related to increased knee and ankle joint strength, eccentric muscular capacity, and maximal force production.

Local Vibration Reduces Muscle Damage after Prolonged Exercise in Men

Prolonged exercise can lead to muscle damage, with soreness, swelling, and ultimately reduced strength as a consequence. It has been shown that whole-body vibration (WBV) improves recovery by reducing the levels of stress hormones and the activities of creatine kinase (CK) and lactate dehydrogenase (LDH). The aim of the study was to demonstrate the effect of local vibration treatment applied after exercise on the level of selected markers of muscle fiber damage. The study involved 12 untrained men, aged 21.7 ± 1.05 years, with a VO₂peak of 46.12 ± 3.67 mL·kg⁻¹·min⁻¹. A maximal intensity test to volitional exhaustion was performed to determine VO₂peak and individual exercise loads for prolonged exercise. The subjects were to perform 180 min of physical effort with an intensity of 50 ± 2% VO₂peak. After exercise, they underwent a 60 min vibration treatment or placebo therapy using a mattress. Blood samples were taken before, immediately after the recovery procedure, and 24 h after the end of the exercise test. Myoglobin (Mb) levels as well as the activities of CK and LDH were recorded. Immediately after the hour-long recovery procedure (vibration or placebo), the mean concentrations of the determined indices were significantly different from baseline values. In the vibration group, significantly lower values of Mb (p = 0.005), CK (p = 0.030), and LDH (p = 0.005) were seen. Differences were also present 24 h after the end of the exercise test. The results of the vibration group compared to the control group differed in respect to Mb (p = 0.002), CK (p = 0.029), and LDH (p = 0.014). After prolonged physical effort, topical vibration improved post-workout recovery manifested by lower CK and LDH activity and lower Mb concentration compared to a control group.

The Effects of Whole-Body Vibration on Fatigue in Vertical Jump Performance and Isometric Mid-Thigh Pull Measures

The purpose of this study is to determine the effects of coupling WBV and acute muscular fatigue to determine its effects on countermovement vertical jump (CMVJ) performance and isometric mid-thigh pull (IMTP). Twenty-eight healthy active adults volunteered for five-day study. Testing sessions 2–5 included one of four conditions: No WBV and no fatigue (CON), WBV and fatigue (WBV + FAT), WBV and no fatigue (WBV), and no WBV and fatigue (FAT). WBV was performed using a frequency of 50 Hz and a low amplitude while performing quarter squats for a total of 4 min with a 30 s rest or work ratio. Lower-body fatigue induced using Bosco fatigue protocol. CMVJ and IMTP were performed on force plates. SPSS was used to perform a 2 × 2 Repeated Measures ANOVA. Significant main effects were found for fatigue in CMVJ-height and CMVJ-peak ground reaction force, no significant main effect for WBV, and no significant interactions. Lower-body fatigue decreases vertical jump performance, and WBV did not attenuate the detrimental effects of lower-body fatigue.

Applying Force Plate Technology to Inform Human Performance Programming in Tactical Populations

Force plate assessments, such as countermovement jumps and isometric mid-thigh pulls, examine performances (e.g., jump height, force, power) and movement strategies (e.g., asymmetries, durations), and are best suited to characterize and monitor physical capabilities, not predict injuries. To begin applying force plate technologies, users must first; (1) develop a data management plan to visualize and capture data over time; (2) select appropriate force plates for their scenario; (3) design appropriate testing protocols to ensure valid and reliable data. Force plate assessments may be added to existing testing, serve as separate testing batteries for annual profile testing to compare individuals and understand initial physical capabilities, or for more frequent testing (i.e., monthly or weekly) to monitor training-related adaptations or neuromuscular fatigue. Although these assessments inform evidence-based program designs, human performance practitioners must understand the considerations for conducting appropriate force plate testing, as well as proper visualizations and management of force plate data. Thus, the aim of this review is to provide evidence-based practices for utilizing force plates in tactical populations (e.g., military, firefighters, police). This includes best practices to implement testing for performance profiling, training adaptations, and monitoring neuromuscular fatigue and force asymmetries. Of note, due to the large amount of force-time metrics to choose from, this article provides general examples of important metrics to monitor and training recommendations based on changes to these force-time metrics, followed by specific examples in three case studies.

Kinetic and Kinematic Analysis of Various Drop Jump Performances in Army Reserve Officer Training Corps Cadets

ABSTRACT

Merrigan, JJ, O'Toole, KB, Wutzke, CJ, and Jones, MT. Kinetic and kinematic analysis of various drop jump performances in army reserve officer training corps cadets. J Strength Cond Res XX(X): 000-000, 2021-The purpose was to examine effects of sex, drop height, and external loads on drop jump mechanics in Reserve Officer Training Corps cadets and whether findings were associated with strength. Males (n = 14) and females (n = 12) completed maximal isokinetic concentric (slow-C and fast-C) and eccentric (slow-E and fast-E) knee extensions and flexions at 60°·s-1 and 180°·s-1. After 72 hours, 3 drop jumps were performed under 3 conditions, (i.e., 30 cm unloaded [30UL], 30 cm loaded 15 kg [30L], and 60 cm unloaded [60UL]). No sex × condition interactions existed for any metric (p > 0.05). The 30L condition resulted in slower eccentric and concentric center of mass (COM) and angular velocities, reduced concentric vertical ground reaction forces (vGRF), and lower jump performances. Although 60UL resulted in greater eccentric COM and angular velocities, peak vGRF, impulse, and rate of force development (p < 0.008), no differences existed in jump performances. Males had faster COM and angular concentric velocities and smaller knee valgus angles, but no different vGRF compared with females. The change in the peak hip angle, because of 60UL, was associated with knee extension eccentric and concentric strength, whereas changes in knee angles were associated with eccentric strength. Likewise, eccentric strength influenced the effects of 30L on landing vGRF more so than concentric strength. Initial strength training is recommended, specifically emphasizing eccentric actions, before performing loaded (15 kg) drop jumps to reduce the increase of landing forces. However, caution may be required when performing drops from 60 cm because of increased forces, although no decline in jump performances were noted.

Identifying Reliable and Relatable Force-Time Metrics in Athletes-Considerations for the Isometric Mid-Thigh Pull and Countermovement Jump

The purpose of this study was to evaluate intrasession reliability of countermovement jump (CMJ) and isometric mid-thigh pull (IMTP) force-time characteristics, as well as relationships between CMJ and IMTP metrics. Division I sport and club athletes (n = 112) completed two maximal effort CMJ and IMTP trials, in that order, on force plates. Relative and absolute reliability were assessed using intraclass correlation coefficients (ICCs) > 0.80 and coefficients of variation (CVs) < 10%. Intrasession reliability was acceptable for the majority of the CMJ force-time metrics except for concentric rate of force development (RFD), eccentric impulse and RFD, and lower limb stiffness. The IMTP's time to peak force, instantaneous force at 150 ms, instantaneous net force, and RFD measures were not reliable. Statistically significant weak to moderate relationships (r = 0.20-0.46) existed between allometrically scaled CMJ and IMTP metrics, with the exception of CMJ eccentric mean power not being related with IMTP performances. A majority of CMJ and IMTP metrics met acceptable reliability standards, except RFD measures which should be used with caution. Provided CMJs and IMTPs are indicative of distinct physical fitness capabilities, it is suggested to monitor athlete performance in both tests via changes in those variables that demonstrate the greatest degree of reliability.

Monitoring Neuromuscular Performance in Military Personnel

A necessarily high standard for physical readiness in tactical environments is often accompanied by high incidences of injury due to overaccumulations of neuromuscular fatigue (NMF). To account for instances of overtraining stimulated by NMF, close monitoring of neuromuscular performance is warranted. Previously validated tests, such as the countermovement jump, are useful means for monitoring performance adaptations, resiliency to fatigue, and risk for injury. Performing such tests on force plates provides an understanding of the movement strategy used to obtain the resulting outcome (e.g., jump height). Further, force plates afford numerous objective tests that are valid and reliable for monitoring upper and lower extremity muscular strength and power (thus sensitive to NMF) with less fatiguing and safer methods than traditional one-repetition maximum assessments. Force plates provide numerous software and testing application options that can be applied to military's training but, to be effective, requires the practitioners to have sufficient knowledge of their functions. Therefore, this review aims to explain the functions of force plate testing as well as current best practices for utilizing force plates in military settings and disseminate protocols for valid and reliable testing to collect key variables that translate to physical performance capacities.