title: Influence of variable resistance loading on subsequent free weight maximal back squat performance.
abstract: 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.
authors.affiliation: 1School of Sport, Exercise and Human Performance, University of Derby, Buxton, United Kingdom; 2Centre for Exercise and Sports Science Research, School of Exercise and Health Sciences, Edith Cowan University, Joondalup, Western Australia; 3Department of Physical Education and Sport Science, University of Thessaly, Greece; and 4Sport, Exercise and Life Sciences, The University of Northampton, Northampton, United Kingdom.
authors.forename: Minas A
authors.initials: MA
authors.lastname: Mina
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Blazevich
authors.forename: Giannis
authors.initials: G
authors.lastname: Giakas
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Kay
mesh_terms: D000293:Adolescent; D000328:Adult; D006801:Humans; D008297:Male; D055815:Young Adult; D054874:Athletic Performance / Q000502:physiology; D001696:Biomechanical Phenomena; D018592:Cross-Over Studies; D004576:Electromyography; D005080:Exercise Test; D007719:Knee Joint / Q000502:physiology; D052097:Quadriceps Muscle / Q000502:physiology; D063996:Warm-Up Exercise / Q000502:physiology; D014891:Weight Lifting / Q000502:physiology