M A Mina

Influence of variable resistance loading on subsequent free weight maximal back squat performance.

Abstract Mina, MA, Blazevich, AJ, Giakas, G, and Kay, AD. Influence of variable resistance loading on subsequent free weight maximal back squat performance. J Strength Cond Res 28(10): 2988–2995, 2014—The purpose of the study was to determine the potentiating effects of variable resistance (VR) exercise during a warm-up on subsequent free-weight resistance (FWR) maximal squat performance. In the first session, 16 recreationally active men (age = 26.0 ± 7.8 years; height = 1.7 ± 0.2 m; mass = 82.6 ± 12.7 kg) were familiarized with the experimental protocols and tested for 1 repetition maximum (1RM) squat lift. The subjects then visited the laboratory on 2 further occasions under either control or experimental conditions. During these conditions, 2 sets of 3 repetitions of either FWR (control) or VR (experimental) squat lifts at 85% of 1RM were performed; during the experimental condition, 35% of the load was generated from band tension. After a 5-minute rest, 1RM, 3D knee joint kinematics, and vastus medialis, vastus lateralis, rectus femoris, and semitendinosus electromyogram (EMG) signals were recorded simultaneously. No subject increased 1RM after FWR, however, 13 of 16 (81%) subjects increased 1RM after VR (mean = 7.7%; p < 0.01). Lower peak and mean eccentric (16–19%; p ⩽ 0.05) and concentric (12–21%; p ⩽ 0.05) knee angular velocities were observed during the 1RM following VR when compared with FWR, however, no differences in knee flexion angle (1.8°; p > 0.05) or EMG amplitudes (mean = 5.9%; p > 0.05) occurred. Preconditioning using VR significantly increased 1RM without detectable changes in knee extensor muscle activity or knee flexion angle, although eccentric and concentric velocities were reduced. Thus, VR seems to potentiate the neuromuscular system to enhance subsequent maximal lifting performance. Athletes could thus use VR during warm-up routines to maximize squat performance.

A sled push stimulus potentiates subsequent 20-m sprint performance

OBJECTIVES The objective of this study was to examine the potentiating effects of performing a single sprint-style sled push on subsequent unresisted 20m sprint performance. DESIGN Randomized crossover design. METHODS Following a familiarization session, twenty rugby league players performed maximal unresisted 20m sprints before and 15s, 4, 8 and 12min after a single sled push stimulus loaded with either 75 or 125% body mass. The two sled push conditions were performed in a randomized order over a one-week period. The fastest sprint time recorded before each sled push was compared to that recorded at each time point after to determine the post-activation potentiation (PAP) effect. RESULTS After the 75% body mass sled push, sprint time was 0.26±1.03% slower at the 15s time point (effect size [ES]=0.07) but faster at the 4 (-0.95±2.00%; ES=-0.22), 8 (-1.80±1.43%; ES=-0.42) and 12 (-1.54±1.54%; ES=-0.36)min time points. Sprint time was slower at all the time points after the 125% body mass sled (1.36±2.36%-2.59±2.90%; ESs=0.34-0.64). CONCLUSIONS Twenty-meter sprint performance is potentiated 4-12min following a sled push loaded with 75% body mass while it is impaired after a 125% body mass sled. These results are of great importance for coaches seeking to potentiate sprint performance with the sled push exercise.

Chain-loaded variable resistance warm-up improves free-weight maximal back squat performance

Abstract The acute influence of chain-loaded variable resistance exercise on subsequent free-weight one-repetition maximum (1-RM) back squat performance was examined in 16 recreationally active men. The participants performed either a free-weight resistance (FWR) or chain-loaded resistance (CLR) back squat warm-up at 85% 1-RM on two separate occasions. After a 5-min rest, the participants attempted a free-weight 1-RM back squat; if successful, subsequent 5% load additions were made until participants failed to complete the lift. During the 1-RM trials, 3D knee joint kinematics and knee extensor and flexor electromyograms (EMG) were recorded simultaneously. Significantly greater 1-RM (6.2 ± 5.0%; p < .01) and mean eccentric knee extensor EMG (32.2 ± 6.7%; p < .01) were found after the CLR warm-up compared to the FWR condition. However, no difference (p > .05) was found in concentric EMG, eccentric or concentric knee angular velocity, or peak knee flexion angle. Performing a CLR warm-up enhanced subsequent free-weight 1-RM performance without changes in knee flexion angle or eccentric and concentric knee angular velocities; thus a real 1-RM increase was achieved as the mechanics of the lift were not altered. These results are indicative of a potentiating effect of CLR in a warm-up, which may benefit athletes in tasks where high-level strength is required.

Stretch imposed on active muscle elicits positive adaptations in strain risk factors and exercise-induced muscle damage

Stretching highly‐contracted plantar flexor muscles (isokinetic eccentric contractions) results in beneficial adaptations in muscle strain risk factors; however its effects in other muscle groups, and on architectural characteristics and exercise‐induced muscle damage (EIMD), are unknown.

Postactivation potentiation of horizontal jump performance across multiple sets of a contrast protocol.

Abstract Seitz, LB, Mina, MA, and Haff, GG. Postactivation potentiation of horizontal jump performance across multiple sets of a contrast protocol. J Strength Cond Res 30(10): 2733–2740, 2016—This study determined whether a postactivation potentiation (PAP) effect could be elicited across multiple sets of a contrast PAP protocol. Fourteen rugby league players performed a contrast PAP protocol comprising 4 sets of 2 paused box squats accommodated with bands alternated with 2 standing broad jumps. The rest period between the squats and the jumps and between the sets was 90 seconds. A control protocol with standing broad jumps only was performed on a separate session. A standing broad jump was performed ∼2 minutes before each protocol and served as a baseline measurement. Standing broad jump distance was significantly greater (4.0 ± 3.4% to 5.7 ± 4.7%) than baseline during the 4 sets of the contrast PAP protocol with the changes being medium in the first, second, and fourth sets (effect size [ES]: 0.58, 0.67, and 0.69, respectively) and large for the third set (ES: 0.81). Conversely, no PAP effect was observed in the control protocol. Additionally, the stronger players displayed a larger PAP effect during each of the 4 sets of the contrast PAP protocol (Cohens d: 0.28–1.68) and a larger mean effect across these 4 sets (Cohens d: 1.29). Horizontal jump performance is potentiated after only 90 seconds of rest after an accommodating exercise, and this PAP effect can be elicited across 4 sets. Additionally, the PAP response is largely mediated by the individuals strength level. These results are of great importance for coaches seeking to incorporate PAP complexes involving horizontal jumps in their training programs.