Backseat Inclination Affects the Myoelectric Activation During the Inclined Leg Press Exercise in Recreationally Trained Men.

ABSTRACT: Marchetti, PH, Gomes, WA, Da Silva, JJ, Magalhaes, RA, Teixeira, LFM, and Whiting, WC. Backseat inclination affects the myoelectric activation during the inclined leg press exercise in recreationally trained men. J Strength Cond Res 37(10): e541-e545, 2023-Changes in the angle between the seat and backrest during the inclined leg press (ILP) exercise may influence myoelectric activity. The purpose of this study was to evaluate the myoelectric activity between 2 different angles between the seat and backrest (90° and 125°) during the ILP exercise in recreationally trained men. Fifteen young, resistance-trained men (age: 26.8 ± 5.3 years, height: 173.8 ± 6.6 cm, total body mass: 81.6 ± 7.6 kg) performed 1 set of 10 repetitions at 70% of their body mass during the ILP exercise using 2 different angles between the seat and backrest (ILP90° and ILP125°). Surface electromyography (peak RMS 90 and iEMG) was used to measure the myoelectric activity of the vastus lateralis (VL), biceps femoris (BF), and gluteus maximus (GM). A paired t test was used to measure differences in knee and hip joint displacement, peak RMS 90 , and iEMG between ILP90 and ILP125. The hip angle presented a greater displacement during the ILP125 when compared with ILP90 ( p < 0.001), considering a similar knee joint displacement. For the VL, there was observed greater myoelectric activation (peak RMS 90 and iEMG) during ILP125 when compared with ILP90 ( p < 0.05). For the BF, there was observed greater myoelectric activation (peak RMS 90 and iEMG) during ILP90 when compared with ILP125 ( p < 0.05). However, GM did not present differences between ILP90 and ILP125. In conclusion, the angle between the seat and backrest (ILP90 or ILP125) altered the myoelectric activation of the VL and BF with no difference for the GM.

Different Knee and Ankle Positions Affect Force and Muscle Activation During Prone Leg Curl in Trained Subjects.

ABSTRACT: Marchetti, PH, Magalhaes, RA, Gomes, WA, da Silva, JJ, Stecyk, SD, and Whiting, WC. Different knee and ankle positions affect force and muscle activation during prone leg curl in trained subjects. J Strength Cond Res 35(12): 3322-3326, 2021-Different joint positions for biarticular muscles may affect force and muscular activity during single-joint exercises. The aim of this study was to compare the maximal isometric contractions and muscle activation in 2 different knee and ankle positions during prone leg curl exercise in trained subjects. Fifteen resistance-trained men (27 ± 4 years, 178.80 ± 5.72 cm, 86.87 ± 12.51 kg) were recruited. The peak force (PF) and muscle activation of biceps femoris, gastrocnemius lateralis (GL), and soleus lateralis (SL) were measured during knee flexion at 0 and 90° and maximal dorsiflexion (D) or plantarflexion (P). Three maximal voluntary isometric contractions of 5 seconds were performed for each combination of knee and ankle positions. Two-way repeated-measures analysis of variances were used for all dependent variables. For PF, there was a significant difference between ankle positions (D × P) at 90° (p = 0.009) and knee positions (0 × 90°) for D (p < 0.001) and P (p < 0.001). Peak force was greater with the knee at 0° and the ankle maximally dorsiflexed. For GL, there was a significant difference between ankle (D × P) at 0° (p = 0.002) and knee positions (0 × 90°) for D (p = 0.005). Gastrocnemius lateralis activation was greater with the knee at 90° of flexion and the ankle maximally dorsiflexed. For SL, there was a significant difference between ankle positions (D × P): at 90° (p = 0.001) and at 0° (p = 0.002). Soleus lateralis is more active in plantarflexion irrespective of the knee joint position. Isometric contractions with full knee extension produce more strength regardless of the ankle position; neither the knee position nor the ankle position may influence the activity of the hamstrings.

Kinematic and sEMG Analysis of the Back Squat at Different Intensities With and Without Knee Wraps.

The purposes of this study were to measure the acute effects of knee wraps (KWs) on knee and hip joint kinematics, dynamic muscle activation from the vastus lateralis (VL) and gluteus maximus (GM), and rating of perceived exertion (RPE) during the back squat exercise at 2 different intensities. Fourteen resistance-trained men (age: 24 ± 4 years, height: 176 ± 6 cm, body mass: 81 ± 11 kg, back squat 1 repetition maximum [1RM]: 107 ± 30 kg, 3 ± 1 year of back squat experience) performed 1 set of 3 repetitions under 4 different conditions, to a depth of approximately 90 degrees of knee joint flexion, and in random order: KWs at 60% 1RM (KW60), KWs at 90% 1RM (KW90), without knee wraps (NWs) at 60% 1RM (NW60), and NWs at 90% 1RM (NW90). The dependent variables obtained were vertical and horizontal bar displacement, peak joint angle in the sagittal plane (hip and knee joints), concentric and eccentric muscle activation (by integrated electromyography) from the VL and GM, and RPE. For muscle activity, there were significant decreases in the VL NWs at 60% 1RM (p = 0.013) and a significant increase NWs at 90% 1RM (p = 0.037). There was a significant increase in VL muscle activity at 90% 1RM, when compared with 60% 1RM (KW: p = 0.001, effect size (ES) = 1.51 and NW: p < 00.001, ES = 1.67). There was a decrease in GM muscle activity NWs only at 60% 1RM (p = 0.014). There was a significant increase in GM muscle activity at 90% 1RM, when compared with 60% 1RM (KW: p < 0.001 and NW: p < 0.001). For peak hip joint flexion angle, there was significant decreases between intensities (90% 1RM < 60% 1RM) only to NWs condition (p = 0.009), and there was greater knee flexion NWs for both intensities: 60% 1RM (p < 0.001) and 90% 1RM (p = 0.018). For normalized vertical barbell displacement, there were significant differences between intensities when using KWs (p = 0.022). There were significant differences in RPE between 60 and 90% 1RM for each condition: KWs (p < 0.001) and NWs (p < 0.001). In conclusion, the use of KWs results in decreased muscle activation of the VL at the same intensity (90% 1RM).

The acute effects of unilateral ankle plantar flexors static- stretching on postural sway and gastrocnemius muscle activity during single-leg balance tasks.

The aim of this study was to investigate the acute effects of unilateral ankle plantar flexors static- stretching on surface electromyography (sEMG) and the center of pressure (COP) during a single-leg balance task in both lower limbs. Fourteen young healthy, non-athletic individuals performed unipodal quiet standing for 30s before and after (stretched limb: immediately post-stretch, 10 and 20 minutes and non-stretched limb: immediately post-stretch) a unilateral ankle plantar flexor static- stretching protocol [6 sets of 45s/15s, 70-90% point of discomfort (POD)]. Postural sway was described using the COP area, COP speed (antero-posterior and medio-lateral directions) and COP frequency (antero-posterior and medio-lateral directions). Surface EMG (EMG integral [IEMG] and Median frequency[FM]) was used to describe the muscular activity of gastrocnemius lateralis. Ankle dorsiflexion passive range of motion increased in the stretched limb before and after the static-stretching protocol (mean ± SD: 15.0° ± 6.0 and 21.5° ± 7.0 [p < 0.001]). COP area and IEMG increased in the stretch limb between pre-stretching and immediately post-stretching (p = 0.015 and p = 0.036, respectively). In conclusion, our static- stretching protocol effectively increased passive ankle ROM. The increased ROM appears to increase postural sway and muscle activity; however these finding were only a temporary or transient effect. Key PointsThe postural control can be affected by static- stretching protocol.The lateral gastrocnemius muscle action was increased after the static- stretching protocol.The static- stretching effects remain for less than 10 minutes.

Differences Between Pullover and Pulldown Exercises on Maximal Isometric Force and Myoelectric Activity in Recreationally-Trained Men.

The aim of the present study was to compare the myoelectric activation and peak force (PF) between pullover (PO) and pulldown (PW) exercises in different shoulder joint positions during maximal isometric contractions (0o, 45o, 90o, 135o, and 180°). Fifteen young, healthy, resistance-trained men were recruited. The participants performed three maximal voluntary isometric contractions for each exercise at five shoulder joint positions. The myoelectric activation (iEMG) from pectoralis major (PM); latissimus dorsi (LD); posterior deltoid (PD), and PF were measured. For PF, there were significant main effects for exercise and joint positions (p < 0.001). For iEMG PM, there was significant a main effect for joint positions (p < 0.001). There was a significant interaction between exercises and joint positions (p < 0.001). For iEMG LD, there was a significant main effect for joint positions (p < 0.001). There was no significant interaction between exercises and joint positions. For iEMG PD, there was a significant main effect for joint positions (p < 0.001). There was no significant interaction between exercises and joint positions. For RPE, there were no significant differences between exercises and joint positions. The study concludes that specific shoulder joint positions affect PF production and iEMG during both exercises. RPE was not affected.

Different volumes and intensities of static stretching affect the range of motion and muscle force output in well-trained subjects.

The manipulation of the volume and intensity of static stretching (SS) can affect the range of motion (ROM) and muscle force output. The purpose of this study was to investigate the effect of two different SS protocols with different intensities (50% and 85% POD) and volumes (120-s and 240-s) on ROM, peak force, and muscle activity during maximal isometric leg curl exercise in well-trained participants. Fifteen young males (age:27.5 ± 6.1years, height:175.6 ± 4.7cm, and body mass:81.5 ± 10.4kg, 6 ± 2 years of resistance training experience) performed passive hip flexion with two different SS protocols: six stretches of 40-s, with 15-sec rest between each stretch at 50% of the point of discomfort (POD) and three stretches of 40-s, with 15-sec rest between each stretch at 85%POD. The passive hip flexion ROM, biceps femoris muscle activation (integrated electromyography: IEMG), and knee flexors force were monitored during a 3-s maximal voluntary isometric leg curl exercise. ROM increased between pre- and post-intervention for both SS protocols (50%POD: p = 0.016, Δ% = 4.6% and 85%POD: p < 0.001, Δ% = 11.42%). Peak force decreased between pre- and post-intervention only for 85%POD (p = 0.004, Δ% = 23.6%). There were no significant IEMG differences. In conclusion, both SS protocols increased ROM, however, the high-intensity and short-duration SS protocol decreased peak force.

NO EFFECT OF KINESIOLOGY TAPE ON PASSIVE TENSION, STRENGTH OR QUADRICEPS MUSCLE ACTIVATION OF DURING MAXIMAL VOLUNTARY ISOMETRIC CONTRACTIONS IN RESISTANCE TRAINED MEN.

BACKGROUND: Kinesiology Tape (KT) is widely used in sports rehabilitation and by those performing physical activity, however, there is no consensus in the scientific literature about its effectiveness on performance, strength or muscle activation.Purpose: The purpose of this study was to measure the acute effects of KT in static rest, and during knee extension maximal voluntary isometric contraction (MVIC) performance in resistance trained men.Study Design: Observational, descriptive, comparative. METHODS: Eighteen young, healthy, trained males (age: 25 ± 6 years, height: 176.0 ± 5 cm, and mass: 81.8 ± 8.0 kg) volunteered to participate. Initially, they were in a relaxed sitting position of 90 degrees knee flexion with their limb supported by the machine lever arm to measure passive tension of the tissues of the knee joint. Then, they performed three MVIC trials of five seconds each with a three-minute rest between trials, in four randomized experimental conditions, with 10-min rest between conditions: (a) control, no taping; (b) Knee Sleeve; (c) KT; and (d) sham. During all MVICs, peak force, impulse, and muscle activation of the vastus lateralis (integrated electromyography [IEMG] and median frequency) were measured. RESULTS: Repeated measures ANOVAs revealed no statistical differences between conditions for passive tension (p > 0.05), peak force (p > 0.05), impulse (p > 0.05), IEMG (p > 0.05), or median frequency (p > 0.05). CONCLUSION: KT does not influence passive tension during static position at 90 degrees of knee flexion. KT does not affect quadriceps activation or force production during a maximal voluntary isometric contraction in the same position. LEVEL OF EVIDENCE: 3a.