Kinetic Responses to External Cues Are Specific to Both the Type of Cue and Type of Exercise in Adolescent Athletes.

ABSTRACT: Barillas, SR, Oliver, JL, Lloyd, RS, and Pedley, J. Kinetic responses to external cues are specific to both the type of cue and type of exercise in adolescent athletes. J Strength Cond Res 37(3): 597-605, 2023-The purpose of this study was to examine how external cues influence kinetics during isometric and dynamic tasks in adolescent athletes. Fifteen adolescent male soccer players performed an isometric midthigh pull (IMTP), unloaded and loaded squat jumps (SJs) (15 and 30% of body mass), countermovement jump (CMJ), and drop jump (DJ) using a neutral or external force-specific or velocity-specific cues. Cue type had limited effects on outcomes in the IMTP or SJs, with mostly trivial ( g < 0.20), nonsignificant differences ( p > 0.05) across kinetic variables. In the CMJ and DJ, a force cue significantly ( p < 0.05) increased jump height ( g = 0.43 & 0.52) compared with a velocity cue, but in the DJ, a force cue significantly increased jump height ( g = 0.52) compared with both a neutral and velocity cue. However, a velocity cue significantly ( p < 0.05) reduced ground contact time ( g = 0.73-1.52) and time to peak force ( g = 0.50-1.29) in both the CMJ and DJ when compared with a force and neutral cue and increased force and power-related measures ( g = 0.33-1.12) in the CMJ and DJ when compared with a force cue. In adolescent athletes, the type of external cue had limited effects on kinetic measures in an IMTP and SJ but differential effects on both a CMJ and DJ, suggesting cues have more effect with increasing movement velocity. Consequently, practitioners working with adolescent athletes should consider both the type of exercise and the desired outcome when providing external cues.

External Cueing Influences Drop Jump Performance in Trained Young Soccer Players.

ABSTRACT: Oliver, JL, Barillas, SR, Lloyd, RS, Moore, I, and Pedley, J. External cueing influences drop jump performance in trained young soccer players. J Strength Cond Res 35(6): 1700-1706, 2021-Drop jump (DJ) characteristics provide insight on power production and injury risk. The purpose of this study was to investigate the effect of external cueing on DJ characteristics in young male soccer players. Fourteen academy soccer players performed DJs with 4 different conditions, control (CONT), contact cue (CC), height cue (HC), and quiet cue (QC). Performance measures were reactive strength index (RSI), jump height, ground contact time (GCT), and take-off impulse, with injury risk reflected by impact peak, impact timing, and landing impulse. Contact cue showed a very large significant reduction in GCT (effect size [ES] > 2.0, p < 0.05), and moderate to large increase in RSI, landing impulse, and push-off impulse (ES 0.70-1.55, p < 0.05) compared with all other conditions. Contact cue also moderately increased impact peak when compared with HC and QC (ES ≥ 0.78, p < 0.05). Height cue led to a significant increase in jump height that was moderately greater than other external cues (ES ≥ 0.87, p < 0.05), but with only a small nonsignificant increase compared (ES 0.54, p > 0.05) with CONT. The data showed that all cues provided a specific response; CC reduced GCT and increased RSI, HC increased jump height, and QC reduced outcomes associated with injury risk. Height cue may be advantageous for young soccer players with a low training age because it shows a small to moderate increase in jump height without increasing injury risk. Young players may need to be safely progressed to be able to use a CC to facilitate high reactive strength without being exposed to undue injury risk.

Effects of Starting Stance on Base Running Sprint Speed in Softball Players.

Speed is a crucial aspect in softball, and can be the difference between winning and losing. Base stealing is a method used to produce runs. There has been debate over which starting position is the most advantageous to maximize acceleration and speed to reach the next base the fastest. The purpose of this study was to examine the effect of different starting stances on acceleration and speed phases in collegiate softball players. Seventeen healthy NCAA Division I women's softball players (age = 19.9 ± 1.3yrs, height = 167.0 ± 5.4cm, mass = 74.8 ± 14.1kg) volunteered to participate. Three maximum 45 ft sprints, with one minute rest, were performed (with splits at 15, 30 and 45ft) for each of three starting stances (front foot on the base, back foot on the base, and cross over stance). A 1×3 repeated measures ANOVA for total time demonstrated that front foot on the base was significantly faster (2.51 ± 0.18s) than back foot on the base (2.70 ± 0.19s) and the cross over step (2.66 ± 0.23s). For all three splits, front foot on the base was also significantly faster (0.96 ± 0.07s, 0.81 ± 0.06s, and 0.73 ± 0.06s) than back foot on the base (1.10 ± 0.13s, 0.84 ± 0.05s, and 0.75 ± 0.43s) and cross over step (1.04 ± 0.09s, 0.84 ± 0.06s, and 0.75 ± 0.07s). The decrease in time for front foot on the base was probably the result of using the base to push against, like a sprinter's block, to produce greater horizontal force to accelerate faster and reach a greater top speed. Coaches should teach their softball athletes to stand with their front foot on the base when base running.

Repeated Plyometric Exercise Attenuates Blood Glucose in Healthy Adults.

Plyometric exercise is popular in commercial exercise programs aiming to maximize energy expenditure for weight loss. However, the effect of plyometric exercise on blood glucose is unknown. The purpose of this study was to investigate the effect of relatively high intensity plyometric exercise on blood glucose. Thirteen subjects (6 females age= 21.8 ± 1.0 yrs.; height= 163.7 ± 7.8 cm; mass= 60.8 ± 6.7 kg and 7 males age= 22.0 ± 2.6 yrs.; height= 182.3 ± 3.6 cm; mass= 87.4 ± 12.5 kg) volunteered to participate. Subjects completed two random conditions on two separate days, consisting of either five sets of 10 maximal effort countermovement squat jumps (SJ) with 50 seconds' rest between sets or quiet sitting (SIT) for the time equated to the SJ duration (~4min). Immediately after each condition, subjects drank 75g of anhydrous glucose (CHO) in 100ml of water. Blood glucose measurements were taken via finger prick pre and immediately post SJ or SIT, and 5, 15, 30, and 60 min post. A 2×6 (condition × time) ANOVA revealed a significant interaction where SJ blood glucose was lower at 15 (114.0 ± 14.6 mg/dl) and 30 (142.1 ± 22.5 mg/dl) min compared to SIT (15min 130.8 ± 14.0 mg/dl and 30min 159.3 ± 21.0 mg/dl). The current plyometric protocol attenuated CHO-induced blood glucose at 15 and 30 min. This may be due to increased physiological stress applied to the muscles, thus increasing muscular glucose uptake.

Determination of Vertical Jump as a Measure of Neuromuscular Readiness and Fatigue.

Watkins, CM, Barillas, SR, Wong, MA, Archer, DC, Dobbs, IJ, Lockie, RG, Coburn, JW, Tran, TT, and Brown, LE. Determination of vertical jump as a measure of neuromuscular readiness and fatigue. J Strength Cond Res 31(12): 3305-3310, 2017-Coaches closely monitor training loads and periodize sessions throughout the season to create optimal adaptations at the proper time. However, only monitoring training loads ignores the innate physiological stress each athlete feels individually. Vertical jump (VJ) is widely used as a measure of lower-body power, and has been used in postmatch studies to demonstrate fatigue levels. However, no pretraining monitoring by VJ performance has been previously studied. Therefore, the purpose of this study was to determine the sensitivity of VJ as a measure of readiness and fatigue on a daily sessional basis. Ten healthy resistance-trained males (mass = 91.60 ± 13.24 kg; height = 179.70 ± 9.23 cm; age = 25.40 ± 1.51 years) and 7 females (mass = 65.36 ± 12.29 kg; height = 162.36 ± 5.75 cm; age = 25.00 ± 2.71 years) volunteered to participate. Vertical jump and BRUNEL Mood Assessment (BAM) were measured 4 times: pre-workout 1, post-workout 1, pre-workout 2, and post-workout 2. Workout intensity was identical for both workouts, consisting of 4 sets of 5 repetitions for hang cleans, and 4 sets of 6 repetitions for push presses at 85% 1 repetition maximum (1RM), followed by 4 sets to failure of back squats (BSs), Romanian deadlift, and leg press at 80% 1RM. The major finding was that VJ height decrement (-8.05 ± 9.65 cm) at pre-workout 2 was correlated (r = 0.648) with BS volume decrement (-27.56 ± 24.56%) between workouts. This is important for coaches to proactively understand the current fatigue levels of their athletes and their readiness to resistance training.

Sled Towing Acutely Decreases Acceleration Sprint Time.

Wong, MA, Dobbs, IJ, Watkins, C, Barillas, SR, Lin, A, Archer, DC, Lockie, RG, Coburn, JW, and Brown, LE. Sled towing acutely decreases acceleration sprint time. J Strength Cond Res 31(11): 3046-3051, 2017-Sled towing is a common form of overload training in sports to develop muscular strength for sprinting. This type of training leads to acute and chronic outcomes. Acute training potentially leads to postactivation potentiation (PAP), which is when subsequent muscle performance is enhanced after a preload stimulus. The purpose of this study was to determine differences between rest intervals after sled towing on acute sprint speed. Twenty healthy recreationally trained men (age = 22.3 ± 2.4 years, height = 176.95 ± 5.46 cm, mass = 83.19 ± 11.31 kg) who were currently active in a field sport twice a week for the last 6 months volunteered to participate. A maximal 30-meter (m) baseline (BL) body mass (BM) sprint was performed (with splits at 5, 10, 20, and 30 m) followed by 5 visits where participants sprinted 30 m towing a sled at 30% BM then rested for 2, 4, 6, 8, or 12 minutes. They were instructed to stand still during rest times. After the rest interval, they performed a maximal 30-m post-test BM sprint. Analysis of variance (ANOVA) revealed that post sled tow BM sprint times (4.47 ± 0.21 seconds) were less than BL times (4.55 ± 0.18 seconds) on an individualized rest interval basis. A follow-up 2 × 4 ANOVA showed that this decrease occurred only in the acceleration phase over the first 5 m (BL = 1.13 ± 0.08 seconds vs. Best = 1.08 ± 0.08 seconds), which may be the result of PAP and the complex relationship between fatigue and potentiation relative to the intensity of the sled tow and the rest interval. Therefore, coaches should test their athletes on an individual basis to determine optimal rest time after a 30-m 30% BM sled tow to enhance acute sprint speed.

Bench Press Upper-Body Muscle Activation Between Stable and Unstable Loads.

The bench press is one of the most commonly used upper-body exercises in training and is performed with many different variations, including unstable loads (ULs). Although there is much research on use of an unstable surface, there is little to none on the use of an UL. The purpose of this study was to investigate muscle activation during the bench press while using a stable load (SL) vs. UL. Twenty resistance-trained men (age = 24.1 ± 2 years; ht = 177.5 ± 5.8 cm; mass = 88.7 ± 13.7 kg) completed 2 experimental conditions (SL and UL) at 2 different intensities (60 and 80% one repetition maximum). Unstable load was achieved by hanging 16 kg kettlebells by elastic bands from the end of the bar. All trial lifts were set to a 2-second cadence with a slight pause at the bottom. Subjects had electrodes attached to 5 muscles (pectoralis major, anterior deltoid, medial deltoid, triceps brachii, and latissimus dorsi) and performed 3 isometric bench press trials to normalize electromyographic data. All 5 muscles demonstrated significantly greater activation at 80% compared with 60% load and during concentric compared with eccentric actions. These results suggest that upper body muscle activation is not different in the bench press between UL and SL. Therefore, coaches should use their preference when designing training programs.