Muscle Activation and Torso Movement during Exercise using Novel Fiberglass Resistance Poles

Background: A novel form of functional training utilizes flexible fiberglass poles for resistance. Similar to elastic bands, as the poles flex, resistance increases. To date, no studies have examined activation patterns associated with such implements. Objective: This study examined muscle activation and torso rotation using different pole resistance intensities during a “push-pull” rotational core exercise. Methods: Twenty-one subjects (16 women, 5 men; age=20.4±1.3y) completed 6 trials of 10 repetitions each of a standing push and pull movement with 3 different pole tensions (very light, light, moderate). Muscle activation (electromyography) for the anterior and posterior deltoid, abdominal oblique, and paraspinal muscles were recorded. Concentric contractions during the push phase (PUSH) and the pull load (PULL) phases were recoded, and percent maximal voluntary contraction (%MVC) was computed. Markers on the acromion process and a vertically mounted camera were used to record torso rotation during each push and pull. ANOVA for each muscle and PUSH and PULL was used for comparisons across pole intensity. Results: Significant main effects for torso rotation were seen, with rotation with the very light pole (Push= 61.9 ± 9.20, Pull= 64.8 ± 14.00) significantly greater than moderate (Push= 52.0 ± 12.80, Pull= 54.9 ± 10.10). EMG data were highly variable, with no differences in muscle activation detected across pole resistance loads. Conclusion: Variability of the EMG data prevent clear resolution of activation patterns. However, torso rotation is limited with heavier pole resistance since increased pole flex also increases resistance.

Accentuated Eccentric Loading is Superior to Traditional Loading for Improving Acute Countermovement Jump Performance in Adult, Resistance-Trained Males

Clinical Scenario: Traditional loading (TL) is a common technique to employ when engaging in countermovement jumps (CMJ). Accentuated eccentric loading (AEL) is a newer modality that is being explored for acute CMJ performance. Focused Clinical Question: In adult, resistance-trained males, will AEL have a superior impact on acute CMJ performance compared to TL? Summary of Key Findings: The literature was searched for studies that examined the influence of AEL on acute CMJ performance compared to a TL protocol. TL was defined as any loading condition that utilized an equivalent resistance during both the eccentric and concentric contractions. Three studies met the inclusion and exclusion criteria, and were identified and included in the critically appraised topic. Each of the 3 studies found that various AEL conditions were either equal to or better than TL when examining subsequent CMJ performance. In no specific CMJ outcome measure was TL deemed to have a greater impact than AEL. Clinical Bottom Line: AEL provides more favorable acute CMJ performance than TL in adult, resistance-trained males. Strength of Recommendation: Consistent findings from 2 randomized crossover studies and one repeated-measured design investigation suggest level 2b evidence to support AEL as an ideal protocol for acute CMJ performance.

Eccentric Exercise Is Powerful but Can Be Painful

Your muscles can contract in different ways: when you walk upstairs, the muscles at the fronts of your thighs shorten (concentric contraction), whereas when you walk downstairs, they lengthen (eccentric contraction). Concentric contractions require more oxygen and thus make you burn more calories. Eccentric contractions are easier but break parts of the muscle and make you feel sore for several days. If you repeat eccentric exercises, however, your muscles will probably get bigger and stronger than they would by repeating concentric contractions. Most physical activities (like running and jumping) include both concentric and eccentric phases. Scientists have designed tools to study each type of muscle contraction, such as eccentric cycling, which uses a bike on which you must resist the pedals as they are driven backward by an engine.

Electromyographic Comparison of Flywheel Inertial Leg Curl and Nordic Hamstring Exercise Among Soccer Players

Purpose: The Nordic hamstring exercise (NHE) has been shown to considerably reduce hamstring injuries among soccer players. However, as the load in the NHE is the person’s own bodyweight, it is a very heavy exercise and difficult to individualize. The flywheel inertial leg curl (FLC) could be an alternative since the eccentric overload is based on the amount of work produced in the concentric movement. Therefore, the primary aim of this study was to compare the activation in the hamstrings at long muscle lengths in the NHE and the FLC in amateur soccer players. Methods: Fifteen male amateur soccer players performed 5 repetitions in each exercise in a randomized and counterbalanced order. The concentric and eccentric movements were divided into lower and upper phases. Surface EMG was measured distally, proximally, and in the middle, at both muscles. Results: In the lower phase in the eccentric movement, there were no significant differences between the 2 exercises (P = .101–.826). In the lower concentric movement, the FLC led to higher activation in all parts of both the biceps femoris (31%–52%, P < .001) and the semitendinosus (20%–35%, P = .001–.023). Conclusion: Both exercises activated the hamstrings similarly at long muscle lengths during eccentric contractions (Nordic hamstring, nonsignificantly higher). However, when performing concentric contractions, the FLC induced higher activations. Therefore, the FLC could be a useful alternative to the NHE and particularly suitable for weaker athletes before progressing to NHE.

Quadriceps activation during maximal isometric and isokinetic contractions: The minimal real difference and its implications

BACKGROUND: A method of measurement of voluntary activation (VA, percent of full muscle recruitment) during isometric and isokinetic concentric contractions of the quadriceps femoris (QF) at 60∘/s and 120∘/s was previously validated. OBJECTIVE: This study aimed to quantify the test-retest minimal real difference (MRD) of VA during isometric (ISOM) and isokinetic concentric contractions of QF (100∘/s, ISOK) in a sample of healthy individuals. METHODS: VA was measured through the interpolated twitch technique. Pairs of electrical stimuli were delivered to the QF at 40∘ of knee flexion during maximal voluntary contractions. Twenty-five healthy participants (20–38 years, 12 women, 13 men) completed two testing sessions with a 14-day interval. VA values were linearized through logit transformation (VAl). The MRD was estimated from intraclass correlation coefficients (model 2.1). RESULTS: The VA (median, range) was 84.20% (38.2–99.9%) in ISOM and 94.22% (33.8-100%) in ISOK. MRD was 0.78 and 1.12 logit for ISOM and ISOK, respectively. As an example, in terms of percent VA these values correspond to a change from 76% to 95% and from 79% to 98% in ISOM and in ISOK, respectively. CONCLUSIONS: The provided MRD values allow to detect significant individual changes in VA, as expected after training and rehabilitation programs.

Effects of trunk extensor eccentric exercise on lipid profile and glycaemic response

ObjectivesA number of previous studies reported physiological responses and adaptations after eccentric muscle contraction of limb muscles. In contrast, no study has determined physiological response after eccentric contraction of trunk muscles. The purpose of the present study was to compare the functional and metabolic changes after eccentric or concentric exercises of trunk extensor muscles.MethodsIn this randomised, crossover study, 10 men performed a single bout of 50 maximal voluntary concentric and eccentric contractions of the trunk extensor with an interval of 2 weeks between bouts. The activities of the paraspinal muscles were recorded during concentric and eccentric contractions. Muscle soreness, muscle function, blood lipid profiles and glycaemic responses were measured before, immediately after and at 24, 48, 72 and 96 hours after each bout.ResultsThe lumbar multifidus and iliocostalis lumborum activities during eccentric contractions were significantly higher than those during concentric contractions (p<0.05). The maximal strength and muscle endurance of the trunk extensor were not decreased even after the eccentric contractions. Compared with concentric contractions, muscle soreness was significantly increased at 24, 48, 72 and 96 hours after eccentric contractions (p<0.05). The TG, TC and LDL-C were significantly lower at 48, 72 and 96 hours after eccentric contractions (p<0.05), while blood glucose levels and HOMA-IR were significantly greater at 48 and 72 hours after eccentric contractions (p<0.05).ConclusionThis study indicated that eccentric contractions of the trunk extensor had positive effects on the lipid profile and the glycaemic response.

Muscle Recruitment Pattern of The Hamstring Muscles in Hip Extension and Knee Flexion Exercises

We aimed to compare dynamic exercise performance between hip extension exercises with different knee angles and between knee flexion exercises with different hip angles, and to investigate the recruitment pattern of the hamstrings in each exercise. Seven men performed 4 isokinetic exercises (3 maximal concentric contractions at 30°/s (peak torque) and 30 maximal concentric contractions at 180°/s (total work)): hip extension with the knee fully extended (HEke) and with the knee flexed at 90° (HEkf) and knee flexion with the hip fully extended (KFhe) and with the hip flexed at 90° (KFhf). The recruitment pattern of the hamstrings was evaluated in each exercise using magnetic resonance imaging (T2 calculation). The HEke condition showed significantly greater peak torque than the HEkf condition (p < 0.05). The KFhf condition had significantly greater peak torque and total work values than the KFhe condition (p < 0.05). Although the biceps femoris long head, semitendinosus, and semimembranosus had significantly increased post-exercise T2 values in the HEke (p < 0.05), KFhe, and KFhf conditions (p < 0.01), the T2 increase values were significantly greater under the KFhf than the HEke condition (p < 0.05). The semitendinosus showed a significantly greater T2 increase value than other muscles under both KFhe and KFhf conditions (p < 0.05). Performance of hip extension and knee flexion exercises increases when the hamstring muscles are in a lengthened condition. The hamstring muscles (particularly the semitendinosus) are more involved in knee flexion than in hip extension.

Effect of Pause Versus Rebound Techniques on Neuromuscular and Functional Performance After a Prolonged Velocity-Based Training

Purpose: A variation of the traditional squat (SQ) rebound technique (REBOUND) including a momentary pause ∼2 seconds (PAUSE) between eccentric and concentric phases has been proposed. Although there is a consensus about the lower acute effects on performance of this PAUSE variant compared with traditional REBOUND technique, no information exists about the differences in longitudinal adaptations of these SQ executions. Methods: A total of 26 men were randomly assigned into the PAUSE (n = 13) or REBOUND (n = 13) groups and completed a 10-week velocity-based training using the SQ exercise, only differing in the technique. Neuromuscular adaptations were assessed by the changes in the 1-repetition maximum strength and mean propulsive velocity achieved against the absolute loads (in kilograms) common to pretest and posttest. Functional performance was evaluated by the following tests: countermovement jump, Wingate, and sprint time at 0 to 10, 10 to 20, and 0 to 20 m. Results: Whereas both groups showed significant increases in most of the neuromuscular tests (P < .05), the PAUSE (effect size [ES] = 0.76–1.12) presented greater enhancements than REBOUND (ES = 0.45–0.92). Although not significant, improvements in Wingate and sprint time at 0 to 10 and 0 to 20 m were higher for PAUSE (ES = 0.31–0.46) compared with REBOUND (ES = 0.10–0.29). Conversely, changes on countermovement jump and sprint time at 10 to 20 m were superior for REBOUND (ES = 0.17–0.88) than for PAUSE (ES = 0.09–0.75). Conclusion: Imposing a pause between eccentric and concentric phases in the SQ exercise could be an interesting strategy to increase neuromuscular and functional adaptations in sport actions that mainly depend on concentric contractions. Moreover, sport abilities highly dependent on the stretch-shortening cycle could benefit from the REBOUND or a combination of the 2 techniques.