Maria L. Nibali

Variability and predictability of elite competitive slalom canoe-kayak performance

Abstract Little is known about the race performance characteristics of elite-level slalom canoeists or the magnitude of improvement necessary to enhance medal-winning prospects. Final placing in this sport is determined by the aggregate of semi-final and final run times inclusive of penalty times. We therefore used mixed linear modelling to analyse these times for finalists ranked in the top and bottom half in the mens canoe, mens kayak, and womens kayak boat classes at World Cups, World Championships, and Olympic Games from 2000 to 2007. The run-to-run variability for top-ranked athletes at different courses ranged from 0.8% to 3.2% (90% confidence limits ×/÷1.11–1.31), reflecting differences in how challenging these courses were. The race-to-race variability of aggregate run time was 1.2–2.1% (×/÷~1.09); 0.3 of this variability yields the smallest worthwhile enhancement of 0.4–0.6%. The variabilities of bottom-ranked finalists were approximately double those of top-ranked finalists. The home advantage was small (0.3–0.8%), and incurring a penalty had a marginal effect on reducing actual run time (0.2–0.7%). Correlation coefficients for performance predictability within competitions (0.06–0.35), within years (0.12–0.47), and between years (0.12–0.43) were poor. In conclusion, the variability of performance and smallest worthwhile enhancements in slalom canoe-kayaking are larger than those of comparable sports, and race outcomes are largely unpredictable.

Influence of rest interval duration on muscular power production in the lower-body power profile

Abstract Nibali, ML, Chapman, DW, Robergs, RA, and Drinkwater, EJ. Influence of rest interval duration on muscular power production in the lower-body power profile. J Strength Cond Res 27(10): 2723–2729, 2013—There is a paucity of evidence-based support for the allocation of rest interval duration between incremental loads in the assessment of the load-power profile. We examined the effect of rest interval duration on muscular power production in the load-power profile and sought to determine if greater rest is required with increasing load (i.e., variable rest interval). Ten physically trained men completed 4 experimental conditions in a crossover balanced design. Participants performed jump squats across incremental loads (0–60 kg) on 4 occasions, with an allocated recovery interval of 1, 2, 3, or 4 minutes. The mean log-transformed power output at each load was used for comparison between conditions (rest intervals). Unloaded jump squats (0 kg) maximized power output at each condition. The maximal mechanical power output was 66.6 ± 6.5 W·kg−1 (1 minute), 66.2 ± 5.2 W·kg−1 (2 minutes), 67.1 ± 5.9 W·kg−1 (3 minutes), and 66.2 ± 6.5 W·kg−1 (4 minutes). Trivial or unclear differences in power output were observed between rest intervals at each incremental load. As expected, power declined per 10 kg increment in load, the magnitude of decrease was 13.9–14.5% (confidence limits [CL]: ±1.3–2.0%) and 13.4–14.6% (CL: ±2.4–3.9%) for relative peak and mean power, respectively, yet differences in power output between conditions were likely insubstantial. The prescription of rest intervals between loads that are longer than 1 minute have a likely negligible effect on muscular power production in the jump squat incremental load-power profile. Practitioners should select either a 1- to 4-minute rest interval to best accommodate the logistical constraints of their monitoring sessions.

Influence of Familiarization and Competitive Level on the Reliability of Countermovement Vertical Jump Kinetic and Kinematic Variables.

Abstract Nibali, ML, Tombleson, T, Brady, PH, and Wagner, P. Influence of familiarization and competitive level on the reliability of countermovement vertical jump kinetic and kinematic variables. J Strength Cond Res 29(10): 2827–2835, 2015—Understanding typical variation of vertical jump (VJ) performance and confounding sources of its typical variability (i.e., familiarization and competitive level) is pertinent in the routine monitoring of athletes. We evaluated the presence of systematic error (learning effect) and nonuniformity of error (heteroscedasticity) across VJ performances of athletes that differ in competitive level and quantified the reliability of VJ kinetic and kinematic variables relative to the smallest worthwhile change (SWC). One hundred thirteen high school athletes, 30 college athletes, and 35 professional athletes completed repeat VJ trials. Average eccentric rate of force development (RFD), average concentric (CON) force, CON impulse, and jump height measurements were obtained from vertical ground reaction force (VGRF) data. Systematic error was assessed by evaluating changes in the mean of repeat trials. Heteroscedasticity was evaluated by plotting the difference score (trial 2 − trial 1) against the mean of the trials. Variability of jump variables was calculated as the typical error (TE) and coefficient of variation (%CV). No substantial systematic error (effect size range: −0.07 to 0.11) or heteroscedasticity was present for any of the VJ variables. Vertical jump can be performed without the need for familiarization trials, and the variability can be conveyed as either the raw TE or the %CV. Assessment of VGRF variables is an effective and reliable means of assessing VJ performance. Average CON force and CON impulse are highly reliable (%CV: 2.7% ×/÷ 1.10), although jump height was the only variable to display a %CV ⩽SWC. Eccentric RFD is highly variable yet should not be discounted from VJ assessments on this factor alone because it may be sensitive to changes in response to training or fatigue that exceed the TE.

Considerations for determining the time course of post-activation potentiation

We sought to determine the efficacy of using a continuous time course trial to assess the temporal profile of post-activation potentiation and to determine the time course of potentiation of discrete jump squat kinetic and kinematic variables. Eight physically trained men performed jump squats before and 4, 8, and 12 min after a 5-repetition maximum back squat. Time intervals were assessed in 3 discontinuous trials (each time interval assessed in a separate trial) and in 1 continuous trial (all time intervals assessed in a single trial). Percentage differences between continuous and discontinuous trials at each time interval were mostly insubstantial. Discrete variables displayed a diverse time course (effect size: trivial to large); time to maximal values ranged between 5.00 ± 2.53 min (concentric peak force) and 9.50 ± 2.98 min (eccentric mean force). Eccentric variables (8.58 ± 3.56 min) took longer to peak than concentric variables (6.64 ± 2.93 min) (effect size: small). Individual subjects attained maximal values for kinetic and kinematic variables at different time intervals, yet the 4-min interval typically displayed the greatest magnitude and frequency of potentiation. We conclude that a continuous time course trial does not substantially influence performance of subsequent jumps and is appropriate for determining the temporal profile of potentiation, which is influenced by discrete jump squat kinetic and kinematic variables and individual differences.