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- Norrbrand, Lena
(författare)
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Acute and early chronic responses to resistance exercise using flywheel or weights
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Resistance exercise using weights typically offers constant external load during coupled shortening (concentric) and lengthening (eccentric) muscle actions in sets of consecutive repetitions until failure. However, the constant external load and the inherent capability of skeletal muscle to produce greater force in the eccentric compared with the concentric action, would infer that most actions are executed with incomplete motor unit involvement. In contrast, use of the inertia of flywheels to generate resistance allows for maximal voluntary force to be produced throughout the concentric action, and for brief episodes of greater eccentric than concentric loading, i.e. “eccentric overload”. Thus, it was hypothesized that acute flywheel resistance exercise would induce greater motor unit and muscle use, and subsequent fatigue, compared with traditional weight stack/free weight resistance exercise. Furthermore, it was hypothesized that flywheel training would induce more robust neuromuscular adaptations compared with training using weights. A total of 43 trained and untrained men were investigated in these studies.Knee extensor muscle activation, fatigue response and muscle use were assessed during exercises by recording electromyographic signals and by means of functional magnetic resonance imaging, respectively. Flywheel resistance exercise provoked maximal or near maximal muscle activation from the first repetition, induced robust fatigue, and prompted more substantial motor unit and muscle use than weight stack/free weight resistance exercise in both novice and resistance trained men. Both prior to and following five weeks of unilateral knee extension training, the eccentric muscle activation was greater with flywheel than weight stack training. Furthermore, weight stack training generated greater increases of dynamic strength and neural adaptations, while flywheel training generated more prominent hypertrophy of individual quadriceps muscles and greater improvement of maximal isometric strength. Hence, due to the preferential metabolic cost of the concentric rather than eccentric actions, the maximal activation through the entire range of the concentric action within each repetition of a set during flywheel resistance exercise probably evoked the marked fatigue, and prompted more substantial muscle use than resistance exercise using weights. Furthermore, while any cause‐effect relationship remains to be determined, results of the pesent study suggest that brief episodes of “eccentric overload” amplify muscular adaptations following concentriceccentric resistance training.
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| 2. |
- Norrbrand, Lena, et al.
(författare)
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Flywheel resistance training calls for greater eccentric muscle activation than weight training
- 2010
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Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 110:5, s. 997-1005
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Tidskriftsartikel (refereegranskat)abstract
- Changes in muscle activation and performance were studied in healthy men in response to 5 weeks of resistance training with or without "eccentric overload". Subjects, assigned to either weight stack (grp WS; n = 8) or iso-inertial "eccentric overload" flywheel (grp FW; n = 9) knee extensor resistance training, completed 12 sessions of four sets of seven concentric-eccentric actions. Pre- and post-measurements comprised maximal voluntary contraction (MVC), rate of force development (RFD) and training mode-specific force. Root mean square electromyographic (EMG(RMS)) activity of mm. vastus lateralis and medialis was assessed during MVC and used to normalize EMG(RMS) for training mode-specific concentric (EMG(CON)) and eccentric (EMG(ECC)) actions at 90°, 120° and 150° knee joint angles. Grp FW showed greater (p < 0.05) overall normalized angle-specific EMG(ECC) of vastii muscles compared with grp WS. Grp FW showed near maximal normalized EMG(CON) both pre- and post-training. EMG(CON) for Grp WS was near maximal only post-training. While RFD was unchanged following training (p > 0.05), MVC and training-specific strength increased (p < 0.05) in both groups. We believe the higher EMG(ECC) activity noted with FW exercise compared to standard weight lifting could be attributed to its unique iso-inertial loading features. Hence, the resulting greater mechanical stress may explain the robust muscle hypertrophy reported earlier in response to flywheel resistance training.
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| 3. |
- Norrbrand, Lena, 1971-, et al.
(författare)
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Quadriceps muscle use in the flywheel and barbell squat
- 2011
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Ingår i: Aviation, Space and Environmental Medicine. - Alexandria, VA : Aerospace Medical Association. - 0095-6562 .- 1943-4448. ; 82:1, s. 13-19
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Tidskriftsartikel (refereegranskat)abstract
- Background: Resistance exercise has been proposed as an aid to counteract quadriceps muscle atrophy in astronauts during extended missions in Orbit. While space authorities have advocated the squat exercise should be prescribed, no exercise system suitable for in-flight use has been validated with regard to quadriceps muscle use. We compared muscle involvement in the terrestrial “gold standard” squat using free weights and a non-gravity dependent flywheel resistance exercise device aimed at use in space. Methods: Ten strength-trained men performed five sets of 10 repetitions using the Barbell Squat (BS; 10 repetition maximum) or Flywheel Squat (FS; each repetition maximal), respectively. Functional magnetic resonance imaging (MRI) and surface electromyography (EMG) techniques assessed quadriceps muscle use. Exercise-induced contrast shift of MR images was measured by means of transverse relaxation time (T2). EMG root mean square (RMS) was measured during concentric (CON) and eccentric (ECC) actions and normalized to EMG RMS determined during maximal voluntary contraction. Results: The quadriceps muscle group showed greater exercise-induced T2 increase following FS compared with BS. Among individual muscles, the rectus femoris displayed greater T2 increase with FS (+24±14%) than BS (+8±4%). Normalized quadriceps EMG showed no difference across exercise modes. Discussion: Collectively, the results of this study suggest that quadriceps muscle use in the squat is comparable, if not greater, with flywheel compared with free weight resistance exercise. Data appears to provide support for use of flywheel squat resistance exercise as a countermeasures adjunct during spaceflight.
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| 4. |
- Norrbrand, Lena, et al.
(författare)
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Resistance training using eccentric overload induces early adaptations in skeletal muscle size
- 2008
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Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 102:3, s. 271-281
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Tidskriftsartikel (refereegranskat)abstract
- Fifteen healthy men performed a 5-week training program comprising four sets of seven unilateral, coupled concentric-eccentric knee extensions 2-3 times weekly. While eight men were assigned to training using a weight stack (WS) machine, seven men trained using a flywheel (FW) device, which inherently provides variable resistance and allows for eccentric overload. The design of these apparatuses ensured similar knee extensor muscle use and range of motion. Before and after training, maximal isometric force (MVC) was measured in tasks non-specific to the training modes. Volume of all individual quadriceps muscles was determined by magnetic resonance imaging. Performance across the 12 exercise sessions was measured using the inherent features of the devices. Whereas MVC increased (P < 0.05) at all angles measured in FW, such a change was less consistent in WS. There was a marked increase (P < 0.05) in task-specific performance (i.e., load lifted) in WS. Average work showed a non-significant 8.7% increase in FW. Quadriceps muscle volume increased (P < 0.025) in both groups after training. Although the more than twofold greater hypertrophy evident in FW (6.2%) was not statistically greater than that shown in WS (3.0%), all four individual quadriceps muscles of FW showed increased (P < 0.025) volume whereas in WS only m. rectus femoris was increased (P < 0.025). Collectively the results of this study suggest more robust muscular adaptations following flywheel than weight stack resistance exercise supporting the idea that eccentric overload offers a potent stimuli essential to optimize the benefits of resistance exercise.
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| 5. |
- Pozzo, Marco, et al.
(författare)
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Muscle-fiber conduction velocity during concentric and eccentric actions on a flywheel exercise device
- 2006
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Ingår i: Muscle and Nerve. - : Wiley. - 0148-639X .- 1097-4598. ; 34:2, s. 169-177
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Tidskriftsartikel (refereegranskat)abstract
- A gravity-independent flywheel exercise device (FWED) has been proven effective as a countermeasure to loss of strength and muscle atrophy induced by simulated microgravity. This study assessed musclefiber conduction velocity (CV) and surface EMG instantaneous mean power spectral frequency (iMNF) during brief bouts of fatiguing concentric (CON) and eccentric (ECC) exercise on a FWED in order to identify electromyographic (EMG) variables that can be used to provide objective indications of muscle status when exercising with a FWED. Multichannel surface EMG signals were recorded from vastus lateralis and medialis muscles of nine men during: (1) isometric, 60-s action at 50% of maximum voluntary action (MVC); (2) two isometric, linearly increasing force ramps (0–100% MVC); and (3) dynamic CON/ECC coupled actions on the FWED. Muscle-fiber CV and iMNF were computed over time during the three tasks. During ramps, CV, but not iMNF, increased with force (P 0.001). Conduction velocity and iMNF decreased with the same normalized rate of change in constant-force actions. During CON/ECC actions, the normalized rate of change over time was larger for CV than iMNF (P 0.05). These results suggest that, during fatiguing, dynamic, variable-force tasks, changes in CV cannot be indirectly inferred by EMG spectral analysis. This underlines the importance of measuring both CV and spectral variables for muscle assessment in dynamic tasks.
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