Comparison of different regression models to fit the force–velocity relationship of a knee extension exercise

The linear regression model provides the force-velocity relationship parameters with the highest reliability

An a-posteriori multicentre reliability study was conducted to compare the between-session reliability of the force-velocity relationship parameters (force-intercept [F0], velocity-intercept [v0], and maximum power [Pmax]) between different regression models during the bench press (BP) and bench press throw (BPT) exercises. Data from four and three studies were considered for the BP (n = 102) and BPT (n = 81) exercises, respectively. The force-velocity relationships were determined using five regression models: linear multiple-point, linear two-point, quadratic polynomial, hyperbolic, and exponential. All regression models provided F0 and Pmax with acceptable reliability (cut-off CV ≤ 9.45%; cut-off ICC ≥ 0.79) with the exceptions of F0 for the quadratic polynomial and hyperbolic models (BPT) and Pmax for the exponential model (BP and BPT). Only the linear multiple- and linear two-point models provided v0 with acceptable absolute reliability (cut-off CV ≤ 7.72%). Regardless of the exercise, the reliability of the three parameters was generally higher for the linear multiple- and two-point models compared to the other models (CVratio ≥ 1.22), and no significant differences were observed between multiple- and linear two-point models (CVratio ≤ 1.11). Linear regression models are recommended to maximise the reliability of the force-velocity relationship parameters during the BP and BPT exercises.

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.

Bilateral and unilateral load-velocity profiling in a machine-based, single-joint, lower body exercise

BACKGROUND

To analyze the goodness of fit of the load-velocity relationship in a machine-based, single-joint exercise performed both in a bilateral and unilateral manner, as well as to study its accuracy to estimate one repetition maximum (1-RM).

METHODS

Fifteen resistance trained males performed an incremental test in the bilateral and unilateral leg extension exercise up to the 1-RM in two separate occasions. Mean vertical velocity of the weight plates in the leg extension machine was measured for every repetition using a smartphone application (My Lift).

RESULTS

Linear regression analyses showed a high goodness of fit (R2 > 0.93) and small standard errors of estimate (SEE < 5%1-RM) both in the bilateral and unilateral leg extension when individual load-velocity regressions for each participant were computed. Unilateral load-velocity relationships showed significant differences in the intercept of the regression line with the Y-axis and the velocity at each percentage of the 1-RM (Cohen's d > 1.0, p< 0.05). Finally, non-significant differences were observed between actual and estimated 1-RM from the load-velocity relationships (r = 0.88.0-96, Cohen's d < 0.2, p> 0.05).

CONCLUSIONS

This proof of concept highlights that computing load-velocity relationships in a machine-based, single-joint, angular exercise can be appropriately performed by measuring the mean vertical velocity of the weight plates. These results could help strength and conditioning researchers and coaches who wish to analyze load-velocity relationship in other common machine-based exercises.

Optimisation of applied loads when using the two-point method for assessing the force-velocity relationship during vertical jumps

This study aimed to compare the reliability and validity of the force-velocity (F-V) relationship parameters obtained from two-point methods differing in the distance between experimental points, and to evaluate the acute change in unloaded jump height after a vertical jump testing procedure based on multiple loads. Totally, 18 men randomly performed two sessions of the squat jump (SJ) and two sessions of the countermovement jump (CMJ) exercises against five external loads (17, 30, 45, 60 and 75 kg). The unloaded jump height was evaluated before and after each testing procedure. Five two-point methods (0-17, 0-30, 0-45, 0-60 and 0-75 kg) and the multiple-point method (0-17-30-45-60-75 kg) were used to model the F-V relationship. The most distant two-point method (0-75 kg) revealed a comparable reliability (CV< 12.1%; ICC> 0.72) and high concurrent validity (r > 0.91) with respect to the multiple-point method (CV< 10.9%; ICC> 0.72). The reliability and validity of the two-point methods decreased with the proximity of the applied loads. Unloaded jump height was significantly reduced after both testing procedures (p < 0.05). These results support the two-point method based on distant loads as a quick and less prone to fatigue procedure for testing the F-V relationship through vertical jumps.

The addition of very light loads into the routine testing of the bench press increases the reliability of the force-velocity relationship

Background

The aim of this study was to examine whether the addition of very light loads for modeling the force–velocity (F–V) relationship during the bench press (BP) exercise can confirm its experimental linearity as well as to increase the reliability and concurrent validity of the F–V relationship parameters (maximum force (F₀), maximum velocity (V₀), F–V slope, and maximum power (P_max)).

Method

The F–V relationship of 19 healthy men were determined using three different methods: (I) 6-loads free method: six loads performed during the traditional free-weight BP exercise (≈ 1–8–29–39–49–59 kg), (II) 4-loads free method: four loads performed during the traditional free-weight BP exercise (≈ 29–39–49–59 kg), and (III) 4-loads Smith method: four loads performed during the ballistic bench press throw exercise in a Smith machine (≈ 29–39–49–59 kg).

Results

The linearity of the F–V relationship was very high and comparable for the three F–V methods (p = 0.204; median Pearson’s correlation coefficient (r) = 0.99). The three methods were ranked from the most to the least reliable as follows: 6-loads free (coefficient of variation (CV) range = 3.6–6.7%) > 4-loads Smith (CV range = 4.6–12.4%) > 4-loads free (CV range = 3.8–14.5%). The higher reliability of the 6-loads free method was especially pronounced for F–V slope (CV_ratio ≥ 1.85) and V₀ (CV_ratio ≥ 1.49) parameters, while the lowest difference in reliability was observed for F₀ (CV_ratio ≤ 1.27). The 6-loads free and 4-loads free methods showed a very high concurrent validity respect to the 4-loads Smith method for F₀ and P_max (r ≥ 0.89), a moderate validity for the F–V slope (r = 0.66–0.82), and a low validity for V₀ (r ≤ 0.37).

Discussion

The routine testing of the F–V relationship of upper-body muscles through the BP exercise should include trials with very light loading conditions to enhance the reliability of the F–V relationship.