Latest in Strength and Conditioning Research

Here are a few abstracts and links to articles published ahead of print, mostly from the Journal of Strength and Conditioning Research.

A Brief Review of Strength and Ballistic Assessment Methodologies in Sport (McMaster et al., 2014)

An athletic profile should encompass the physiological, biomechanical, anthropometric and performance measures pertinent to the athlete’s sport and discipline. The measurement systems and procedures used to create these profiles are constantly evolving and becoming more precise and practical. This is a review of strength and ballistic assessment methodologies used in sport, a critique of current maximum strength [one-repetition maximum (1RM) and isometric strength] and ballistic performance (bench throw and jump capabilities) assessments for the purpose of informing practitioners and evolving current assessment methodologies. The reliability of the various maximum strength and ballistic assessment methodologies were reported in the form of intra-class correlation coefficients (ICC) and coefficient of variation (%CV). Mean percent differences TeX and effect size (ES = [X method2 − X method1] ÷ SDmethod1) calculations were used to assess the magnitude and spread of methodological differences for a given performance measure of the included studies.

Studies were grouped and compared according to their respective performance measure and movement pattern. The various measurement systems (e.g. force plates, position transducers, accelerometers, jump mats, optical motion sensors and jump-and-reach apparatuses) and assessment procedures (i.e. warm-up strategies, loading schemes and rest periods) currently used to assess maximum isometric squat and mid-thigh pull strength (ICC > 0.95; CV < 2.0 %), 1RM bench press, back squat and clean strength (ICC > 0.91; CV < 4.3 %), and ballistic (vertical jump and bench throw) capabilities (ICC > 0.82; CV < 6.5 %) were deemed highly reliable. The measurement systems and assessment procedures employed to assess maximum isometric strength [M Diff = 2–71 %; effect size (ES) = 0.13–4.37], 1RM strength (M Diff = 1–58 %; ES = 0.01–5.43), vertical jump capabilities (M Diff = 2–57 %; ES = 0.02–4.67) and bench throw capabilities (M Diff = 7–27 %; ES = 0.49–2.77) varied greatly, producing trivial to very large effects on these respective measures. Recreational to highly trained athletes produced maximum isometric squat and mid-thigh pull forces of 1,000–4,000 N; and 1RM bench press, back squat and power clean values of 80–180 kg, 100–260 kg and 70–140 kg, respectively. Mean and peak power production across the various loads (body mass to 60 % 1RM) were between 300 and 1,500 W during the bench throw and between 1,500 and 9,000 W during the vertical jump. The large variations in maximum strength and power can be attributed to the wide range in physical characteristics between different sports and athletic disciplines, training and chronological age as well as the different measurement systems of the included studies.

The reliability and validity outcomes suggest that a number of measurement systems and testing procedures can be implemented to accurately assess maximum strength and ballistic performance in recreational and elite athletes, alike. However, the reader needs to be cognisant of the inherent differences between measurement systems, as selection will inevitably affect the outcome measure. The strength and conditioning practitioner should also carefully consider the benefits and limitations of the different measurement systems, testing apparatuses, attachment sites, movement patterns (e.g. direction of movement, contraction type, depth), loading parameters (e.g. no load, single load, absolute load, relative load, incremental loading), warm-up strategies, inter-trial rest periods, dependent variables of interest (i.e. mean, peak and rate dependent variables) and data collection and processing techniques (i.e. sampling frequency, filtering and smoothing options).
Strength and Ballistic Assessment in Sport (McMaster et al., 2014)

The reliability of Functional Movement Screening (FMS) and in-season changes in physical function and performance among elite rugby league players (Waldron et al., 2014)

This study aimed to 1) assess the reliability of the FMS protocol and 2) to establish changes in both FMS and tests of physical performance throughout a season. The reliability of the FMS components (12 in total) was assessed via a non-parametric statistical approach, based on two trials, separated by one week. Score on the FMS, strength (3 RM full-squat, 1 RM bench press), running speed (10 & 40 m) and jump height of 12 elite male under-19 rugby league players was monitored at pre-, mid- and late-season periods. There was no bias (P > 0.05) found between trials for the FMS, with the majority of components reaching 100% ‘perfect agreement’, reflecting the good reliability of the FMS tool. There were no effects (P > 0.05) of season stage on any of the FMS components; however, an improvement (P < 0.05) between the pre- and both mid- and late-season periods was apparent in every component of fitness, such as 1 RM bench-press (112.92 +/- 24.54 kg; 125.83 +/- 21.41 kg; 125.98 +/- 24.48 kg) and 40 m sprint time (5.69 +/- 0.35 s; 5.62 +/- 0.31 s; 5.64 +/- 0.27 s). Our findings demonstrate that the FMS can be reliably administered to elite rugby league players but will not change in accordance with physical performance across a competitive season. Our findings should not necessarily deter practitioners from using the FMS but begin to question the specific qualities that are being assessed through its administration.

Influence of Contrast Shower and Water Immersion on Recovery in Elite Netballers (Peiffer et al., 2014)

Contrast water therapy is a popular recovery modality in sport; however, appropriate facilities can often be difficult to access. Therefore, the present study examined the use of contrast showers as an alternative to contrast water therapy for team sport recovery. In a randomized, cross-over design ten elite female netball athletes (mean +/- SD; age: 20 +/- 0.6 y, height: 1.82 +/- 0.05 m, body mass: 77.0 +/- 9.3 kg) completed three experimental trials of a netball specific circuit followed by one of the following 14 min recovery interventions; (1) contrast water therapy (alternating 1 min 38[degrees]C and 1 min 15[degrees]C water immersion), (2) contrast showers (alternating 1 min 38[degrees]C and 1 min 18[degrees]C showers) or (3) passive recovery (seated rest in 20[degrees]C). Repeated agility, skin and core temperature and perception scales were measured pre, immediately post, 5 h and 24 h post-exercise. No significant differences in repeated agility were evident between conditions at any time point. No significant differences in core temperature were observed between conditions however, skin temperature was significantly lower immediately after contrast water therapy and contrast showers compared with the passive condition. Overall perceptions of recovery were superior following contrast water therapy and contrast showers compared with passive recovery. The findings indicate contrast water therapy and contrast showers did not accelerate physical recovery in elite netballers after a netball specific circuit; however, the psychological benefit from both interventions should be considered when determining the suitability of these recovery interventions in team sport.

Differences in lower body stiffness between levels of netball competition (Pruyn et al., 2014)

There are many notable differences in physical and skill attributes between competition levels, especially in team sports. Stiffness is an important mechanical factor to measure when considering athletic performance and injury incidence. Active vertical stiffness (Kvert) during hopping and passive stiffness during lying and standing were measured during the preseason period for 46 female netballers (24.0 +/- 3.7 years, 72.2 +/- 7.6 kg, 175.2 +/- 6.7 cm). Participants were classified as elite, sub-elite, representative or recreational based on their current level of competition. A one-way ANOVA revealed that elite players possessed significantly higher Kvert than recreational players (p = 0.018). Large effect sizes (ES) suggested that elite players also possessed higher Kvert than sub-elite (d = 1.11) and representative (d = 1.11) players. A number of large and moderate ES were also present when comparing the passive stiffness of elite players to their lower ranked counterparts. The results of this study suggest that elite players possess higher levels of active stiffness when compared to their lower ranked counterparts. The differences in stiffness levels may contribute to a player’s ability to physically perform at an elite level, and also provide one explanation into elevated rates of injury at higher levels of competition.

Velocity based training of lower limb to improve absolute and relative power outputs in concentric phase of half-squat in soccer players (Ramirez et al., 2014)

Purpose: The power production is force-velocity related. We hypothesized that speed based training of lower limb using half-squat can lead to absolute and relative power improvement in concentric movement, with a same external load.

Methods: One group of 19 soccer players (age 24.4 yr, SD = 3.7 yr) participated in a pretest-posttest power training protocol, consistent in 2 training sessions per week during 10 weeks, targeted to work the leg power by performing half-squat with fixed external load (M = 71.7; SD = 5.4), at 65% of 1RM. Measurements of power (absolute -W-, and relative -W/kg-), force (N) and velocity (m/s) (mean and peak) were made from a concentric movement of a half-squat exercise with a fixed external load.

Results: The training protocol increased relative power (M = 47.5, SD = 47.5; p < .001) and absolute power (M = 169.2; SD = 95.5; p < .001). Also, number of repetitions (M = 2.9; SD = 2.4; p < .01), force (M = 66.6; SD = 36.7; p < .001) and velocity (M = .1; SD = .1; p < .001) were increased. However, only improved velocity was related to changes in absolute (r = .939; p < .001) and relative (r = .757; p < .001) power.

Conclusion: The speed based training, combined with moderate to high external load can lead to an improvement of absolute and relative power in concentric phases of half-squat in soccer players. This could be important for improving the performance of the players in the field.

Influence of the intensity of squat exercises on the subsequent jump performance (Fukutani et al., 2014)

Jump performance can be enhanced after performing squat exercises, and this is thought to be due to the phenomenon of postactivation potentiation (PAP). However, the influence of the intensity of squat exercises on jump performance enhancement and its association to PAP have not been elucidated. Thus, we examined the influence of the intensity of squat exercises on the subsequent jump performance and the magnitude of PAP. Eight weight lifters (age, 19.8 +/- 1.3 years; height, 1.67 +/- 0.07 m; body mass, 77.1 +/- 14.8 kg) were recruited as subjects. The intensity of squat exercises was set in two conditions: Heavy condition (HC) (45% 1 repetition maximum [1RM] x 5 repetitions [reps], 60% 1RM x 5 reps, 75% 1RM x 3 reps, and 90% 1RM x 3 reps) and Moderate condition (MC) (45% 1RM x 5 reps, 60% 1RM x 5 reps, and 75% 1RM x 3 reps). Before and after the squat exercises, the subjects performed counter-movement jumps three times. In addition, a twitch contraction was concurrently elicited before and after the squat exercises. In both conditions, twitch torque and jump height recorded after the squat exercises increased significantly compared with those recorded beforehand. The extents of increase in both twitch torque and jump height were significantly larger in HC than in MC. We conclude therefore that a high-intensity squat exercise is better than a moderate-intensity squat exercise as a warm-up modality for enhancing subsequent jump performance.