investigated the relationships between sprint kayak performance and force–time characteristics achieved from a generic lower-limb isometric strength test (which is commonly used in strength testing) and an isometric strength test that assess the pushing ability of the upper limb. Moreover, although force–time
Danny Lum and Abdul Rashid Aziz
Jason Lake, Peter Mundy, Paul Comfort, John J. McMahon, Timothy J. Suchomel, and Patrick Carden
variables (Table 2 ). The largest limits of agreement were found for jump height (2.1%), time to takeoff (3.4%), and reactive strength index modified (3.8%; Table 2 ). Table 2 Results of the Comparison Between CMJ Force–Time Characteristics Obtained From the Laboratory and Portable Force Plate Systems
Dean Norris, David Joyce, Jason Siegler, James Clock, and Ric Lovell
, however, there is a paucity of research examining the recovery time course of force–time characteristics generated from the IMTP following competitive match play. Furthermore, there is limited information regarding the typical week-to-week variation in the recovery time course of these parameters, which
Ernest Baiget, Joshua Colomar, and Francisco Corbi
of the tennis serve (ie, cocking, acceleration and deceleration phases) last around 650 milliseconds, the acceleration phase corresponding to concentric muscle activation lasts about 80 milliseconds. 9 From this perspective, force–time characteristics such as the rate of force development (RFD
Mikko Virmavirta, Juha Kivekäs, and Paavo Komi
The effect of skis on the force–time characteristics of the simulated ski jumping takeoff was examined in a wind tunnel. Takeoff forces were recorded with a force plate installed under the tunnel floor. Signals from the front and rear parts of the force plate were collected separately to examine the anteroposterior balance of the jumpers during the takeoff. Two ski jumpers performed simulated takeoffs, first without skis in nonwind conditions and in various wind conditions. Thereafter, the same experiments were repeated with skis. The jumpers were able to perform very natural takeoff actions (similar to the actual takeoff) with skis in wind tunnel. According to the subjective feeling of the jumpers, the simulated ski jumping takeoff with skis was even easier to perform than the earlier trials without skis. Skis did not much influence the force levels produced during the takeoff but they still changed the force distribution under the feet. Contribution of the forces produced under the rear part of the feet was emphasized probably because the strong dorsiflexion is needed for lifting the skis to the proper flight position. The results presented in this experiment emphasize that research on ski jumping takeoff can be advanced by using wind tunnels.
Joshua Thomas, Thomas Murphy, Steve Tran, Samuel J. Howarth, David Starmer, and Martha Funabashi
110 to 130 milliseconds (Figure 2 ). 13 , 17 , 21 Figure 1 —Hand position during the spinal manipulative therapy used in this study. Figure 2 —Spinal manipulative therapy force–time characteristics: (A) peak preload force, (B) total peak force, (C) time to peak, and (D) loading rate. Instrumentation
Thomas Dos’Santos, Christopher Thomas, Paul A. Jones, and Paul Comfort
To investigate the within-session reliability of bilateral- and unilateral-stance isometric midthigh-pull (IMTP) force–time characteristics including peak force (PF), relative PF, and impulse at time bands (0–100, 0–200, 0–250, and 0–300 milliseconds) and to compare isometric force–time characteristics between right and left and dominant (D) and nondominant (ND) limbs.
Professional male rugby league and multisport male college athletes (N = 54; age, 23.4 ± 4.2 y; height, 1.80 ± 0.05 m; mass, 88.9 ± 12.9 kg) performed 3 bilateral IMTP trials and 6 unilateral-stance IMTP trials (3 per leg) on a force plate sampling at 600 Hz.
Intraclass correlation coefficients (ICCs) and coefficients of variation (CVs) demonstrated high within-session reliability for bilateral and unilateral IMTP PF (ICC = .94, CV = 4.7–5.5%). Lower reliability measures and greater variability were observed for bilateral and unilateral IMTP impulse at time bands (ICC = .81–.88, CV = 7.7–11.8%). Paired-sample t tests and Cohen d effect sizes revealed no significant differences for all isometric force–time characteristics between right and left limbs in male college athletes (P >.05, d ≤ 0.32) and professional rugby league players (P > .05, d ≤ 0.11); however, significant differences were found between D and ND limbs in male college athletes (P < .001, d = 0.43–0.91) and professional rugby league players (P < .001, d = 0.27–0.46).
This study demonstrated high within-session reliability for unilateral-stance IMTP PF, revealing significant differences in isometric force–time characteristics between D and ND limbs in male athletes.
Jill L. McNitt-Gray, Takashi Yokoi, and Carl Millward
In this study, drop height and landing mat composition were hypothesized to influence the landing strategies preferred by female gymnasts. Adjustments in strategy in response to changes in drop height and mat composition were identified by comparison of mechanical variables characterizing two-foot competition-style drop landings from three heights onto two different mats varying in composition (i.e., soft vs. stiff). Force-time characteristics of the landings were quantified (1000 Hz) by a force plate fully supporting the mat. Segment kinematics were recorded simultaneously with shuttered video (60 Hz). Significant differences (ANOVA; p < .05) in peak vertical force, landing phase time, time to peak vertical force, and lower extremity kinematics were found across drop heights. Only time to vertical impact peak and minimum knee angular position produced significant differences between the soft and stiff mats. These results indicate changes in drop height and mat composition may elicit changes in landing strategies of female gymnasts.
Jill L McNitt-Gray, Takashi Yokoi, and Carl Millward
In this study, landing strategies of gymnasts were hypothesized to change with different landing surfaces. This hypothesis was tested by comparing the kinematics and reaction force-time characteristics of two-foot competition-style drop landings performed by male and female collegiate gymnasts onto three surfaces (soft mat, stiff mat, no mat). Significantly lower peak vertical forces, longer landing phase times, and greater knee and hip flexion were observed between the no mat condition and the mat conditions. Knee flexion and peak knee flexion velocities were also observed to be significantly greater for landings on the stiff mat than those on the soft mat. These results indicate that the gymnasts in this study modulated total body stiffness in response to changes in landing surface conditions by using a multi joint solution. In addition, the presence of a mat may reduce the need for joint flexion and may alter the vertical impulse characteristics experienced during landing.
Antti Mero and Paavo V. Komi
This study was undertaken to compare force-time characteristics, muscle power, and electromyographic (EMG) activities of the leg muscles in maximal sprinting and in selected bounding and jumping exercises. Seven male sprinters performed maximal bounding (MB), maximal stepping (MS), maximal hopping with the right (MHR) and left (MHL) legs, and maximal sprint running (MR). These “horizontal” exercises and running were performed on a force platform. EMG activity was telemetered unilaterally from five leg muscles during each trial. The results indicated significant (p < .001) differences among the studied exercises in velocity, stride length, stride rate, flight time, and contact time. Also, significant differences were noticed in reactive forces (p < .01-.001) and power (p < .01) among the performances, whereas only insignificant differences were observed in EMG patterns. The average resultant forces during the braking and propulsion phases in MS, MHR, and MHL were greater (p < .001) than in MR and MB. Stepping and hopping are cyclic and sprint-specific and may be used as strength exercises for sprinters because of great strength demand.