Lower Neuromuscular Activation Research Articles

Impact of resistance training status on trunk muscle activation in a fatiguing set of heavy back squats

PurposeIn this study we measured neural activation (EMG) in four trunk stabilizer muscles and vastus lateralis (VL) in trained and novice participants during a set of squat repetitions to volitional fatigue at 85% 1RM.MethodsForty males were recruited into two groups, novice (NG: n = 21) and experienced (EG: n = 19), according to relative squat 1RM. Participants were tested twice to: (1) determine squat 1RM, and (2) complete a single set of repetitions to volitional fatigue at 85% 1RM. Relative squat 1RM; NG < 140% body mass, EG > 160% body mass. Neuromuscular activation was measured by EMG for the following: rectus abdominus (RA), external oblique (EO), lumbar sacral erector spinae (LSES), upper lumbar erector spinae (ULES) and VL in eccentric and concentric phase. Completed repetitions, RPE and EMG in repetition 1 and at 20, 40, 60, 80 and 100% of completed repetitions were analysed.ResultsNo group differences were found between number repetitions completed and RPE in repetitions to volitional fatigue at 85% 1RM. Neuromuscular activation increased significantly in all muscle groups in eccentric and concentric phase apart from RA in the eccentric phase. Trunk neuromuscular activation was higher in NG compared to EG and this was significant in EO, LSES and ULES in eccentric phase and LSES in the concentric phase. VL activation increased in both phases with no group differences.ConclusionTrunk neuromuscular activation increases in a fatiguing set of heavy squats regardless of training status. Increased back squat strength through training results in lower neuromuscular activation despite greater absolute external squat loads.

Acute Neuromuscular Activity in Selected Injury Prevention Exercises with App-Based versus Personal On-Site Instruction: A Randomized Cross-Sectional Study.

Introduction A significant step towards sport-related injury prevention is the introduction of easily accessible smartphone applications (apps). However, it is unknown whether this type of app-based instruction facilitates similar acute neuromuscular and biomechanical characteristics of the preventive exercises as achieved when instructed on-site by an expert. Thus, the aim was to evaluate acute neuromuscular characteristics observed during a single bout of selected lower extremity injury preventive exercises instructed by an on-screen app versus on-site individual instruction provided by a physiotherapist. Methods In a cross-sectional study design, 47 female football and handball players were randomly assigned to receive app instruction (APP group) or on-site instruction provided by a physiotherapist (PHY group) while performing five lower extremity injury preventive exercises. The exercises performed comprised (1) one-legged balance on Airex, (2) vertical drop jump, (3) one-legged horizontal jump onto floor, (4) one-legged horizontal jump onto Airex, and (5) two-hand Kettlebell Swing. Primary outcome was hamstring (biceps femoris and semitendinosus) muscle activity. Secondary outcomes were quadriceps (vastus lateralis and medialis) muscle activity, as well as hip and knee joint angles. Muscle activity was monitored by surface electromyography (EMG) and normalized to the peak amplitude obtained during a maximal voluntary isometric contraction (MVC). Hip and knee joint angles were recorded by a 3D motion analysis system. A linear mixed model was used to evaluate the differences between experimental conditions for each outcome variable. Results Medial hamstring (semitendinosus) muscle activity was significantly higher during one-legged jump onto Airex (17 percentage points (95% CI 7 to 27)) and Kettlebell Swing (19 percentage points (95% CI 2 to 36)) in the PHY group than the APP group. Likewise, the PHY group demonstrated 18 percentage points (95% CI 1 to 35) and 19 percentage points (95% CI 0 to 38), greater lateral quadriceps muscle (vastus lateralis) activity during one-legged jump onto floor and one-legged jump onto Airex, respectively, compared with that of the APP group. Conclusions Complex exercises, i.e., Kettlebell Swing and one-legged jump onto Airex, are characterized by lower neuromuscular activity when using app-based instructions compared with on-site instruction provided by a physiotherapist. However, the effectiveness of app-based instruction versus on-site individual instruction in injury prevention interventions remains to be investigated in future longitudinally studies.

Exercise performance and neuromuscular activity at a fixed level of RPE following manipulation of peripheral physiological status

PURPOSE: to analyse the effect of manipulation of peripheral physiological status on performance and neuromuscular activity during cycling at a fixed level of RPE. METHODS: following familiarisation trials, seven well trained individuals completed two exercise trials following ingestion of 0.2g.kg-1 NaHCO3 or a CaCO3 placebo which were performed in a randomised and blind manner. During exercise participants were required to cycle at exercise intensity equivalent to their perception of an RPE of 16 on the Category Ratio Scale. Blood pH was measured pre- and post-exercise, and power output, EMG activity in the active musculature, and heart rate were recorded continuously throughout exercise. Exercise was terminated when power output fell below 80% of the average recorded over the first 3 minutes of each trial. RESULTS: pre-exercise pH was higher following NaHCO3 ingestion, but post-exercise values did not differ between NaHCO3 and placebo trials. Exercise duration was 21% longer following NaHCO3 than the placebo, but no significant differences were found in power output or heart rate between trials at any point. EMG activity was higher throughout NaHCO3 trials. CONCLUSIONS: the findings of this study suggest that NaHCO3 ingestion enhanced exercise duration by allowing an increased volume of exercise to be performed prior to individuals reaching individual critical threshold values for pH. Lower neuromuscular activity despite a similar power output following NaHCO3 suggests that perceptions of effort may be based on absolute work rates rather than afferent physiological feedback, and that the work rate is achieved through regulation of efferent neural drive.