Effects of Different Loading Types on the Validity and Magnitude of Force-Velocity Relationship Parameters.

BACKGROUND: Force-velocity (F-V) relationship models gained popularity as a tool for muscle mechanical assessment. However, it is not clear whether the validity of the F-V relationship parameters (maximal theoretical force [F0], velocity [V0] and power [Pmax]) is affected using different load types: gravitational (W, rubber bands pulling the barbell downward), inertial (I, rubber bands pulling the barbell, which is equalized to the weight of the added plates upward), and combined (W + I, weight of the plates). HYPOTHESIS: Load type would affect both the magnitude and validity of F-V relationship parameters. The highest magnitude and validity was expected for F0 using a W, for V0 using an I, and for Pmax using a W + I load. STUDY DESIGN: Cross-sectional. LEVEL OF EVIDENCE: Level 3. METHODS: A total of 13 resistance-trained men (body mass, 87.7 ± 11.2 kg and body height, 183.9 ± 6.4 cm) performed bench press (BP) throws (BPTs) using 3 types of loads against 30 to 80 kg. The validity of F-V relationship parameters was explored with respect to the tests used traditionally for force (maximal voluntary contraction and 1-repetition maximum [1RM]), velocity (maximal velocity achieved during almost unloaded tasks), and power (BPT against the 50%1RM and medicine ball throws) assessment. RESULTS: The W + I loading promoted the highest values of F0 and Pmax, while the highest magnitude of V0 was promoted by the I loading. The validity was acceptable for F0 obtained using the 3 loading conditions with respect to the BP 1RM (r range, 0.30-0.83), and V0 obtained using the I loading with respect to the stick throw (r = 0.54). CONCLUSION: The magnitude of the F-V relationship parameters is affected by load type, but their validity with respect to standardized tests is comparable, with the exception of the higher validity of V0 when obtained using the I loading. CLINICAL RELEVANCE: Any load type can be used for assessing F0, while I load should be selected when assessing V0.

Assessment of Countermovement Jump: What Should We Report?

The purpose of the present study was (i) to explore the reliability of the most commonly used countermovement jump (CMJ) metrics, and (ii) to reduce a large pool of metrics with acceptable levels of reliability via principal component analysis to the significant factors capable of providing distinctive aspects of CMJ performance. Seventy-nine physically active participants (thirty-seven females and forty-two males) performed three maximal CMJs while standing on a force platform. Each participant visited the laboratory on two occasions, separated by 24-48 h. The most reliable variables were performance variables (CV = 4.2-11.1%), followed by kinetic variables (CV = 1.6-93.4%), and finally kinematic variables (CV = 1.9-37.4%). From the 45 CMJ computed metrics, only 24 demonstrated acceptable levels of reliability (CV ≤ 10%). These variables were included in the principal component analysis and loaded a total of four factors, explaining 91% of the CMJ variance: performance component (variables responsible for overall jump performance), eccentric component (variables related to the breaking phase), concentric component (variables related to the upward phase), and jump strategy component (variables influencing the jumping style). Overall, the findings revealed important implications for sports scientists and practitioners regarding the CMJ-derived metrics that should be considered to gain a comprehensive insight into the biomechanical parameters related to CMJ performance.

The Novel Single-Stroke Kayak Test: Can It Discriminate Between 200-m and Longer-Distance (500- and 1000-m) Specialists in Canoe Sprint?

PURPOSE: To test whether the force-velocity (F-V) relationship obtained during a specific single-stroke kayak test (SSKT) and during nonspecific traditional resistance-training exercises (bench press and prone bench pull) could discriminate between 200-m specialists and longer-distance (500- and 1000-m) specialists in canoe sprint. METHODS: A total of 21 experienced male kayakers (seven 200-m specialists and 14 longer-distance specialists) participated in this study. After a familiarization session, kayakers came to the laboratory on 2 occasions separated by 48 to 96 hours. In a randomized order, kayakers performed the SSKT in one session and the bench press and bench pull tests in another session. Force and velocity outputs were recorded against 5 loads in each exercise to determine the F-V relationship and related parameters (maximum force, maximum velocity, F-V slope, and maximum power). RESULTS: The individual F-V relationships were highly linear for the SSKT (r = .990 [.908, .998]), bench press (r = .993 [.974, .999]), and prone bench pull (r = .998 [.992, 1.000]). The F-V relationship parameters (maximum force, maximum velocity, and maximum power) were significantly higher for 200-m specialists compared with longer-distance specialists (all Ps ≤ .047) with large effect sizes (≥0.94) revealing important practical differences. However, no significant differences were observed between 200-m specialists and longer-distance specialists in the F-V slope (P ≥ .477). CONCLUSIONS: The F-V relationship assessed during both specific (SSKT) and nonspecific upper-body tasks (bench press and bench pull) may distinguish between kayakers specialized in different distances.

Magnitude and reliability of mechanical outputs obtained during loaded squat jumps performed from different knee angles.

This study aimed to explore the effect of the knee angle and loading condition on the magnitude and reliability of squat jump (SJ) performance variables. Thirteen male sport sciences students performed in a random order 4 SJ types (knee angle of 80º [SJ80], 90º [SJ90], 100º [SJ100], and self-preferred [SJpref]) against 3 external loads. The push-off distance (HpO), jump height (Hmax), maximum force (Fmax) and maximum power (Pmax) were obtained from force platform recordings. The HpO during the SJpref (43.4 ± 6.4 cm) was always between SJ90 (44.3 ± 4.8 cm) and SJ100 (40.5 ± 4.2 cm). The magnitudes of Hmax, Fmax and Pmax were comparable or higher during the SJpref. The increase of the knee angle was associated with larger values of Fmax and Pmax, but no significant differences were observed for Hmax. An acceptable reliability was observed for HpO (coefficient of variation [CV]≤5.09% and intraclass correlation coefficient [ICC]≥0.78), Hmax (CV≤6.06% and ICC≥0.84), Fmax (CV≤3.25% and ICC≥0.96) and Pmax (CV≤2.93% and ICC≥0.96). Reliability did not systematically differ between the 4 SJ types. In conclusion, the higher magnitudes and comparable reliability of the performance variables obtained during the SJpref support its use for testing lower-body ballistic performance against different loads.