Jan Malecek

Effective mass reflects the body mass mechanically coupled during impact. Acceleration-based effective-mass estimates require noise-sensitive differentiation of segment kinematics. This study introduced a new operational index, the contact-integrated impulse-transfer index (ITI; the ratio of contact impulse to pre-impact foot velocity) and evaluated its reliability, agreement with an acceleration-based effective-mass estimate (M_e,acc), and sensitivity to a carried-load condition. Forty male military cadets performed five maximal front kicks onto a force plate synchronized with three-dimensional motion capture under two fixed-order conditions: barefoot without load and with 30 kg of carried equipment. Reliability was assessed using intraclass correlation coefficients; condition differences using paired tests with effect sizes and false-discovery-rate correction; method agreement using correlations, ICCs, and Bland–Altman analysis; and isokinetic strength interactions using body-mass-adjusted mixed-effects models. ITI showed poor-to-moderate single-kick reliability (ICC = 0.46–0.52) but good reliability for the five-kick mean (ICC = 0.83–0.87). It was higher with than without the carried load (26.18 ± 5.20 vs. 21.72 ± 5.05 kg; p < 0.001; d_z = 1.07), which, by definition, corresponded to a 23% greater net impulse with unchanged pre-impact foot velocity. Net impulse alone was more reliable (single-kick ICC = 0.75; five-kick mean ICC = 0.95) and showed a larger load effect (d_z = 1.39) than ITI. Contact duration increased, peak force decreased, and the force–time profile appeared more push-like under load. In a subsample with usable impact-phase marker trajectories (n = 20), ITI and M_e,acc were not significantly correlated (r = 0.06, p = 0.69) and showed negligible agreement (ICC = 0.01; Bland–Altman bias = −20.6 kg). The condition × strength interactions for concentric hip-rotator strength did not remain significant after Bonferroni correction (adjusted p = 0.067–0.096). Averaged across repeated kicks, ITI is an index of impulse transfer rather than effective (inertial) mass; front kick assessment in soldiers should include representative military equipment, and the altered kick mechanics suggest that training should include it as well.

Effective mass reflects the body mass mechanically coupled during impact. Acceleration-based effective-mass estimates require noise-sensitive differentiation of segment kinematics. This study introduced an impulse-based estimate (M_e,imp = J/v_pre) and evaluated its reliability, agreement with an acceleration-based estimate (M_e,acc), and sensitivity to a carried-load condition. Forty male military cadets performed five maximal front kicks onto a force plate synchronized with three-dimensional motion capture under two fixed-order conditions: barefoot without load (NL) and with 30 kg of carried equipment (WL). Reliability was assessed using intraclass correlation coefficients; condition differences using paired tests with effect sizes and FDR correction; method agreement using correlations, ICCs, and Bland–Altman analysis; and isokinetic strength interactions using body-mass-adjusted mixed-effects models. M_e,imp showed poor-to-moderate single-kick reliability but good reliability for the five-kick mean (ICC = 0.84–0.87). It was higher in WL than NL (25.95 ± 5.44 vs. 21.89 ± 5.14 kg; p < 0.001; d_z = 0.92), reflecting a 21% greater net impulse, while pre-impact foot velocity (v_pre) remained unchanged. Contact duration increased and the force–time profile became more push-like under WL. In a subsample with usable impact-phase marker trajectories (n = 20), M_e,imp and Me,acc were not significantly correlated (r = 0.10, p = 0.54) and showed negligible agreement (ICC = 0.02; Bland–Altman bias = −21.5 kg). Stronger concentric hip rotators were associated with a smaller WL–NL increase in M_e,imp (Bonferroni-adjusted p = 0.044–0.050). M_e,imp should be interpreted as a contact-integrated index of impulse-transfer capacity, reliable when averaged across repeated kicks, rather than as true inertial mass or an interchangeable substitute for Me,acc.

Maleček, J, Malíř, R, Mašek, D, Matoušek, O, Ojanen, T, Oláh, V, Omcirk, D, Šimsa, J, Tufano, J, Vágner, M, and Třebický, V. From test to task: Relevance of basic physical fitness metrics in the context of military-specific performance. J Strength Cond Res XX(X): 000–000, 2026—Physical fitness assessments, such as push-ups, sit-ups, and 12-minute runs, remain central to military readiness evaluation; however, their capacity to explain variance in military-specific task performance remains insufficiently understood. This study investigated the relationship between these physical fitness assessments and performance in 6 simulated military-specific tasks. Twenty-nine physically active men (mean age = 22.6 years, SD = 3.0) completed the following fitness tests: maximal oxygen uptake (V̇ o ₂ max), body composition, aerobic endurance (12-minute run), anaerobic agility (shuttle run), muscular endurance (push-ups, sit-ups, pull-ups), explosive power (countermovement jump, seated medicine ball throw), grip strength, and maximal strength (1-repetition maximum hexagonal barbell deadlift). In addition, 6 military-specific tasks were performed in standardized 10.4-kg combat gear: 2 km loaded march, casualty drag, maximal single lift of a military pack, repeated lift and carry, modified fire and movement, and water can carry. Among the assessments, the only consistent field predictor was the 12-minute Cooper run, which related to both the 2 km loaded march ( β = −0.233, [–0.327 to −0.140]) and repeated lift and carry ( β = −0.062, [–0.089 to −0.034]). By contrast, strength and power measures were more task-specific: maximal single lift was associated with the seated medicine ball throw ( β = 0.112, [0.046 to 0.179]) and grip strength ( β = 0.685, [0.147 to 1.222]), while modified fire and movement time aligned with shuttle-run performance ( β = 0.963, [0.204 to 1.721]). These results suggest that military-specific tasks may provide a more valid criterion for occupational performance, with limited added predictive value of traditional tests beyond the Cooper run.

Introduction: The physical fitness and body composition of soldiers are critical for operational readiness and overall health. Military service demands optimal levels of muscle strength, endurance, and cardiorespiratory fitness, alongside a healthy body fat percentage (%BF). However, unlike in the U.S. Armed Forces, Czech Soldiers are not required to meet specific %BF standards, and the prevalence of excessive fat remains unknown. Dual-energy X-ray absorptiometry (DXA) offers a precise and reliable assessment of body composition, yet its use in European military research remains limited. This study evaluates the body composition of Czech Artillery Soldiers using DXA, focusing on %BF, fat-free mass, visceral adipose tissue (VAT), and bone mineral density (BMD), compares %BF values with U.S. Army and civilian norms, and evaluates the practical implications of these findings for military health policy. Materials and Methods: A randomized cross-sectional study was conducted on 209 healthy adult active-duty Czech Artillery Soldiers (189 men, 20 women). Participants underwent a DXA scan to assess body composition using a Hologic Horizon system. Statistical analyses included the Mann-Whitney and Kruskal-Wallis tests, 1-way ANOVA, and generalized linear models (GLM) with age as a covariate. Health classifications were derived using BMI, %BF, and VAT thresholds for cardiometabolic risk and BMD T-scores for osteopenia and osteoporosis. The protocol adhered to the approval granted by the relevant institutional ethics committee (No. 246/2021). Results: Czech Artillery Soldiers and U.S. Soldiers had nearly identical %BF, 24.3% in Czech men vs. 24.3% in U.S. men; 33.8% vs. 33.3% in women, respectively. Overall, excessive %BF (≥25%) was observed in 41.2% of participants. Age group was a significant predictor of VAT (ω2 = 0.20, df = 6, H = 42.51, P < .001) and %BF (ω2 = 0.07, df = 6, H = 18.73, P < .005), with older participants exhibiting higher levels. High prevalence of osteopenia was found, reaching 20% in both sexes. Contrary to expectations, the GLM revealed that there are no significant differences among units of the Czech Artillery Brigade in any measured variable when age is considered. Conclusions: DXA-measured body composition in Czech Artillery Soldiers closely matches contemporary U.S. Army values. The high prevalence of overweight and osteopenia underscores the need for preventive and educational strategies addressing both metabolic and skeletal health risks. Future research should determine the prevalence of osteopenia and osteoporosis across the Czech Armed Forces to inform appropriate screening practices and targeted interventions.

Background: Serve speed in tennis can be influenced by physical strength and toss kinematics, yet their interaction remains unclear in junior athletes. This study investigated the relationships between toss-related variables (zenith height, impact height, and zenith–impact differential), shoulder rotation strength, and serve speed in junior tennis players. Methods: Thirteen nationally ranked junior male players (mean age: 15.8 ± 0.9 years; body mass: 65.9 ± 5 kg; height: 181 ± 7 cm) participated. Isokinetic shoulder internal and external rotation strength (concentric/eccentric at 210°/s and 300°/s) were measured. High-speed 3D motion capture (Qualisys) recorded toss zenith, impact height and zenith–impact differential during flat serves directed into a designated 1 × 2 m target zone. Serve speed was measured by a radar gun. Correlation, mediation, and moderation analyses were conducted (n = 13; sensitivity ρ ≥ 0.69 for 80% power). Results: Impact height showed a significant positive correlation with successful (ρ = 0.746, p = 0.003) and unsuccessful serve speed (ρ = 0.776, p = 0.002). Moderation analyses showed that lower variability in impact height (p = 0.043) and in zenith–impact differential (p = 0.048) significantly strengthened the association between shoulder-rotator strength and serve speed. Conclusions: Moderation analyses revealed that lower variability in impact height and in the zenith–impact differential strengthened the relationship between shoulder strength and serve speed. Preliminary evidence suggests that consistent toss execution could enhance the translation of shoulder-rotation strength into serve speed in junior players.

Background/Objectives: Serve speed in tennis can be influenced by physical strength and toss kinematics, yet their interaction remains unclear in junior athletes. This study investigated how toss-related variables (zenith height, impact height, and zenith–impact differential) relate to shoulder rotation strength and serve speed in junior tennis players. Methods: Thirteen nationally ranked junior male players (mean age: 15.8 ± 0.9 years; body mass: 65.9 ± 5 kg; height: 181 ± 7 cm) participated. Isokinetic shoulder internal and external rotation strength (concentric/excentric) were measured at 210°/s and 300°/s. High-speed 3D motion capture (Qualisys) recorded toss zenith, impact height, and zenith–impact differential during flat serves directed into a designated 1 × 2 m target zone. Serve speed was assessed using radar gun. Correlation, mediation, and moderation analyses were conducted. Results: Impact height showed a significant positive correlation with successful (ρ = 0.746, p = 0.003) and unsuccessful serve speed (ρ = 0.776, p = 0.002). Moderation analyses showed that lower variability in impact height (p = 0.043) and in zenith–impact differential (p = 0.048) significantly strengthened the association between shoulder-rotator strength and serve speed. Conclusions: Moderation analyses revealed that lower variability in impact height and in the zenith–impact differential strengthened the relationship between shoulder strength and serve speed. These findings suggest that training should emphasize toss consistency to maximize the translation of shoulder rotation strength into serve speed.

Oláh, V, Třebický, V, Maleček, J, Michalička, V, Wąsik, J, and Vágner, M. Is countermovement jump height and one repetition maximum back squat associated with the peak force of a front kick with and without carried load? J Strength Cond Res 39(8): 880–889, 2025—The front kick is a fundamental technique used in self-defense and hand to hand combat. This study aimed to test whether front kick performance, both with and without a 30-kg carried load, can be effectively estimated or tracked through commonly available testing procedures such as the countermovement jumps (CMJ) and one repetition maximum back squat (1RM BS). In 2 testing sessions, 21 male participants (mean age = 22.7 years, SD = 1.9) performed 1RM BS, 5 front kicks peak force (FK) without and with 30-kg carried load (FK30), and 3 CMJ without and with 30-kg carried load (CMJ30). A force plate measured the peak force ( N ) of the FK and FK30 and the height (cm) of the CMJ and CMJ30. Statistically significant correlations were found between CMJ and FK ( r = 0.55 [0.225–1], p = 0.005) and CMJ and 1RM BS ( r = 0.54 [0.219–1, p = 0.005]). Carried load reduced both CMJ height by 61% ( d = 3.35 [2.543–∞], p < 0.001) and FK peak force by 23% ( d = 1.33 [0.828–∞], p < 0.001), compared without load condition. A regression model using 1RM BS and CMJ explained 31.5% of FK variance, with only the height of CMJ being statistically significantly associated, β = 0.626, p = 0.015. The study demonstrates that although there is a relationship between explosive power and maximum strengths, FK is more related to CMJ height than 1RM BS. From a practical standpoint, the study suggests that explosive power shows a better association with the FK than the maximal strength. Thus, training programs focused on lower limb explosive power could allow athletes and military personnel to achieve higher FK. Combat sports trainers and hand-to-hand combat instructors may thus consider accordingly updating their training schemes, emphasizing plyometrics and other explosive training methods for enhancing the peak force of kicks.

Oláh, V, Třebický, V, Maleček, J, Michalička, V, Wąsik, J, and Vágner, M. Is countermovement jump height and one repetition maximum back squat associated with the peak force of a front kick with and without carried load? J Strength Cond Res XX(X): 000-000, 2025-The front kick is a fundamental technique used in self-defense and hand to hand combat. This study aimed to test whether front kick performance, both with and without a 30-kg carried load, can be effectively estimated or tracked through commonly available testing procedures such as the countermovement jumps (CMJ) and one repetition maximum back squat (1RM BS). In 2 testing sessions, 21 male participants (mean age = 22.7 years, SD = 1.9) performed 1RM BS, 5 front kicks peak force (FK) without and with 30-kg carried load (FK30), and 3 CMJ without and with 30-kg carried load (CMJ30). A force plate measured the peak force (N) of the FK and FK30 and the height (cm) of the CMJ and CMJ30. Statistically significant correlations were found between CMJ and FK (r = 0.55 [0.225-1], p = 0.005) and CMJ and 1RM BS (r = 0.54 [0.219-1, p = 0.005]). Carried load reduced both CMJ height by 61% (d = 3.35 [2.543-∞], p < 0.001) and FK peak force by 23% (d = 1.33 [0.828-∞], p < 0.001), compared without load condition. A regression model using 1RM BS and CMJ explained 31.5% of FK variance, with only the height of CMJ being statistically significantly associated, β = 0.626, p = 0.015. The study demonstrates that although there is a relationship between explosive power and maximum strengths, FK is more related to CMJ height than 1RM BS. From a practical standpoint, the study suggests that explosive power shows a better association with the FK than the maximal strength. Thus, training programs focused on lower limb explosive power could allow athletes and military personnel to achieve higher FK. Combat sports trainers and hand-to-hand combat instructors may thus consider accordingly updating their training schemes, emphasizing plyometrics and other explosive training methods for enhancing the peak force of kicks.

Objectives: The relationship between the isokinetic maximal strength of internal or external shoulder rotation and serve speed in tennis is well established, yet the influence of segmental mass, height, and high-speed shoulder rotation strength on serve performance in junior players remains unclear. This study aimed to investigate the relationship between concentric or eccentric isokinetic shoulder strength, segmental mass, height, and first-serve speed aimed at the T-target zone. Methods: Fifteen male junior competitive tennis players (mean ± SD: age 15.9 ± 0.9 years; height: 180.1 ± 7.2 cm; body mass: 66.1 ± 5.7 kg) were assessed for maximal isokinetic strength during concentric and eccentric internal and external shoulder rotations. Segmental mass (arm, leg, and trunk) was measured using dual-energy X-ray absorptiometry, and serve speed was recorded using a radar gun. Results: Concentric shoulder rotations at 210°/s demonstrated significant positive correlations with serve speed for both external (ρ = 0.71, p ≤ 0.01) and internal rotation (ρ = 0.61, p ≤ 0.05). Although lean arm mass partially mediated the relationship between shoulder strength and serve speed (indirect effect = 0.502, 95% CI: −0.156 to 1.145), this mediation effect was not statistically significant. Height was moderately correlated with serve speed (ρ = 0.68, p ≤ 0.01) but did not moderate the relationship between shoulder strength and serve speed. Conclusions: Concentric shoulder strength at higher angular velocities and segmental mass contribute to serve speed in junior tennis players. While height provides structural advantages, strength and lean mass play important roles, emphasizing the need for targeted training programs.

Objectives: The relationship between isokinetic maximal strength of internal or external shoulder rotation and serve speed in tennis is well-established, yet the influence of segmental mass, height, and high-speed shoulder rotation strength on serve performance in junior players remains unclear. This study aimed to investigate the relationship between concentric or eccentric isokinetic shoulder strength, segmental mass, height, and first-serve speed aimed at the T-target zone. Methods: Fifteen male junior competitive tennis players (mean ± SD: age 15.9 ± 0.9 years; height 180.1 ± 7.2 cm; body mass 66.1 ± 5.7 kg) were assessed for maximal isokinetic strength during concentric and eccentric internal and external shoulder rotations. Segmental mass (arm, leg, and trunk) was measured using dual-energy X-ray absorptiometry, and serve speed was recorded using a radar gun. Results: Concentric shoulder rotations at 210°/s demonstrated significant positive correlations with serve speed for both external (ρ = 0.71, p ≤ 0.01) and internal rotation (ρ = 0.61, p ≤ 0.05). Although lean arm mass partially mediated the relationship between shoulder strength and serve speed (indirect effect = 0.502, 95% CI: −0.156 to 1.145), this mediation effect was not statistically significant. Height was moderately correlated with serve speed (ρ = 0.68, p ≤ 0.01) but did not moderate the relationship between shoulder strength and serve speed. Conclusions: Concentric shoulder strength at higher angular velocities and segmental mass contribute to serve speed in junior tennis players. While height provides structural advantages, strength and lean mass play important roles, emphasizing the need for targeted training programs.