The Time-Course of Changes in Muscle Mass, Architecture and Power During 6 Weeks of Plyometric Training

Purpose: To investigate the time-course of changes in knee-extensors muscle mass, architecture and function in response to plyometric training (PLT) performed on a novel training device, the Tramp-Trainer. This machine consists in a trampoline connected to an inclined sledge which allows the performance of repeated jumps while the subject is sitting on a chair. Methods: Eight healthy males (173.6 \ub1 4.7 cm, 69.7 \ub1 13.5 kg, 25.3 \ub1 4.6 years) underwent 6 weeks of bilateral PLT on the tramp-trainer machine. Training was performed three times per week (between 120 and 150 bounces per session). Knee-extensor maximum voluntary torque (MVT) and power, quadriceps femoris (QF) volume (VOL), cross-sectional area from the 20% to the 60% of femur length and CSAmean, together with vastus lateralis (VL) architecture (fascicle length, Lf, and pennation angle, PA) were assessed after 2, 4, and 6 weeks of PLT. Results: All results are presented as changes versus baseline values. MVT increased by 17.8% (week 2, p < 0.001) and 22.2% (week 4, p < 0.01), respectively, and declined to 13.3% (p < 0.05) at week 6 of PLT. Power increased by 18.2% (week 4, p < 0.05) and 19.7% (week 6, p < 0.05). QF VOL increased by 4.7% (week 4, p < 0.05) and 5.8% (week 6, p < 0.01); VL VOL increased by 5.2%, (p < 0.05), 8.2%, (p < 0.01), and 9.6% (p < 0.05) at weeks 2, 4, and 6, respectively. An increase in Lf was detected already at wk 2 (2.2%, p < 0.05), with further increase at 4 and 6 weeks of PLT (4 and 4.4%, respectively, p < 0.01). PA increased by 5.8% (p < 0.05) at week 6. Significant positive correlations were found between CSAmean and Power (R2 = 0.46, p < 0.001) and between QF VOL and Power (R2 = 0.44, p < 0.024). Conclusions: PLT induced rapid increases in muscle volume, fascicle length, pennation angle, torque and power in healthy younger adults. Notably, changes in VL VOL and Lf were detectable already after 2 weeks, followed by increases in knee extensors VOL and power from week 4 of PLT. Since the increase in CSAmean and QF VOL cannot fully explain the increment in muscle power, it is likely that other factors (such as adaptations in neural drive or tendon mechanical properties) may have contributed to such fucntional changes

Positive energy balance is associated with accelerated muscle atrophy and increased erythrocyte glutathione turnover during 5 wk of bed rest

Background: Physical inactivity is often associated with positive energy balance and fat gain. Objective: We aimed to assess whether energy intake in excess of requirement activates systemic inflammation and antioxidant defenses and accelerates muscle atrophy induced by inactivity. Design: Nineteen healthy male volunteers were studied before and at the end of 5 wk of bed rest. Subjects were allowed to spontaneously adapt to decreased energy requirement (study A, n = 10) or were provided with an activity-matched diet (study B, n = 9). Groups with higher (HEB) or lower (LEB) energy balance were identified according to median values of inactivity-induced changes in fat mass (\u394FM, assessed by bioelectrical impedance analysis). Results: In pooled subjects (n = 19; median \u394FM: 1.4 kg), bed rest-mediated decreases in fat-free mass (bioelectrical impedance analysis) and vastus lateralis thickness (ultrasound imaging) were significantly greater (P < 0.03) in HEBAB (-3.8 \ub1 0.4kg and -0.32 \ub1 0.04 cm, respectively) than in LEBab (-2.3 \ub1 0.5 kg and -0.09 \ub1 0.04 cm, respectively) subjects. In study A (median \u394FM: 1.8 kg), bed rest-mediated increases in plasma leptin, C-reactive protein, and myeloperoxidase were greater (P < 0.04) in HEBA than in LEBA subjects. Bed rest-mediated changes of glutathione synthesis rate in eythrocytes (L-[3,3-2H2]cysteine incorporation) were greater (P = 0.03) in HEBA (from 70 \ub1 19 to 164 \ub1 29%/d) than in LEBA (from 103 \ub1 23 to 84 \ub1 27%/d) subjects. Conclusions: Positive energy balance during inactivity is associated with greater muscle atrophy and with activation of systemic inflammation and of antioxidant defenses. Optimizing caloric intake may be a useful strategy for mitigating muscle loss during period of chronic inactivity

Human muscle fascicle behavior in agonist and antagonist isometric contractions

Introduction: The aim of this study was to compare, at a given level of electromyographic (EMG) activity, the behavior of dorsiflexor and plantarflexor muscles as assessed via their architecture (pennation angle and fiber length) during agonist or antagonist isometric contractions. Methods: Realtime ultrasonography and EMG activity of gastrocnemius medialis (GM) and tibialis anterior (TA) muscles were obtained while young males performed ramp isometric contractions in dorsiand plantarflexion. Results: For both muscles, at a similar level of EMG activity, fiber length was longer, and pennation angle was smaller, during antagonist than during agonist contractions. Conclusions: These results indicate that, at similar levels of EMG activity, GM and TA muscles elicit a higher mechanical output while acting as an antagonist. These findings have important implications for muscle function testing. They show that estimation of antagonistic force using the common method based on the EMG/net torque relationship yields underestimated values

ANTAGONIST FORCES ARE UNDERESTIMATED WHEN ASSESSED USING EMG-TORQUE RELATIONSHIP

Introduction Antagonist force production cannot be calculated directly in vivo and is usually estimated by using the relationship between surface EMG activity and exerted torque of the antagonist muscles, while they act as agonists (Maganaris et al., 1998; Mademli et al., 2004; Kellis et al., 1997). An implicit assumption of this method is that during an isometric contraction, the relationship between the level of EMG activity and the mechanical output is the same when a muscle is acting either as an agonist or as an antagonist. If this were the case, one would expect changes in EMG to match changes in architecture (Hodges et al., 2003) in both conditions. Therefore, the aim of this study was to investigate whether the behaviour of Gastrocnemius Medialis muscle (GM) - as assessed by its architecture - would be identical during isometric agonist and antagonist contractions at equal level of EMG activity. Methods Torque, architecture (pennation angle and fiber length) and EMG activity of GM were obtained while 8 young healthy males performed ramp isometric contractions in dorsi-flexion (DF) and plantar-flexion (PF) up to maximal voluntary contractions (MVC). Results At a given EMG activity, GM fiber length was significantly shorter while performing a sub-maximal PF contraction than during DF MVC (-18%; p < 0.001). Similarly, pennation angle during sub-maximal PF was significantly larger than during DF MVC (+28 %; p = 0.014). Discussion At a given level of GM EMG activity,architectural parameters were significantly different when the muscle acted as agonist or antagonist: fiber length was longer, and pennation angle was smaller during antagonist than during agonist isometric contractions. These findings indicate that GM elicits a higher mechanical output while acting as an antagonist when EMG activity is matched. This means that estimation of antagonistic force using the common method based on the EMG/net torque relationship yields underestimated values. References Hodges PW, Pengel LH, Herbert RD, Gandevia SC. (2003). Muscle Nerve;27(6):682-692 Kellis E, Baltzopoulos V. (1997). Eur J Appl Physiol Occup Physiol;76(3):253- 259 Mademli L, Arampatzis A, Morey-Klapsing G, Bruggemann GP. (2004). J Electromyogr Kinesiol;14(5):591-597 Maganaris CN, Baltzopoulos V, Sargeant AJ. (1998). Exp Physiol;83(6):843-85

The lower economy and efficiency of walking in older adults

Healthy septuagenarians with no gait impairment have an elevated cost of walking which is not explained by an elevation in whole body mechanical work. Increased antagonist muscle co-activation (possibly an adaptation to ensure adequate joint stability) may offer partial explanation of the elevated cost of walking

Prevalence of sarcopenia and impact of resistive exercise in a fully independent elderly population

Sarcopenia, the age-associated loss of muscle mass (Narici&Maffulli, 2010) is a main determinant of functional impairment and physical disability in old age. However, the prevalence of sarcopenia amongst fully independent individuals and its reversibility in response to resistive training (RT) are scarcely known. Hence, this study aimed at establishing (i) the prevalence of sarcopenia in fully independent older individuals and (ii) the efficacy of a 12-week RT programme in reversing sarcopenia and its associated muscle weakness. METHODS 26 participants (14 men and 12 women), aged 65-83 yrs, were recruited for this study and underwent 12-week of RT, (3 times/week, 3 sets,14-16 reps), on a leg press machine. Pre- and post-training measurements included: Skeletal Muscle Index (SMI, by bioelectrical impedance); Gait speed (GS) over 4 m; Stair climbing power (SCP); Muscle Architecure of vastus lateralis muscle (pennation angle (Ɵ) and muscle thickness (MT) measured by ultrasonography); 1RM on the leg press. Data were analyzed with descriptive statistics and paired Student’s t-test. RESULTS Before training the prevalence of type I sarcopenia was 61.5% and of type II was 38.5% (classified according to Janssen, 2002). Considering the changes in functional performance, 77% participants (20/26) were responders, while 23% of the participants were non-responders (6 out of 26). For the responders, SMI increased by 2.5% (29.5±4.7 vs 30.3±4.5 %, p50% of a population of fully independent older individuals (65+ yrs), and that significant improvements in muscle mass, strength are afforded by resistive training. It is noteworthy that these structural and functional gains are associated with a net improvement in key activities of daily living such as stair climbing

Comparison between whole body vibration and static resistance training in postmenopausal women : long-term effects on quadriceps muscle volume and power

Introduction. Reductions in muscle mass, force and peak power occurring with aging markedly affect the quality of life of elderly people, particularly regarding the performance of daily activities such as walking, stair negotiation and standing up. However, resistance training has been shown to play a useful role in counteracting these impairments. Recently, Whole Body Vibration (WBV) exercise has been promoted as an alternative and feasible method to enhance strength and muscle performance. Although WBV seems to acutely increase muscle strength and power, its long-term efficacy on muscle structural and functional properties is still controversial and strictly controlled studies are lacking in literature (Rehn et al. 2007). Whether WBV is effective in combating sarcopenia and muscle weakness in old age is thus unknown. Aim of the study. The aim of this research was to compare the long-term effects of a pure vibration training regime with an exercise protocol based on the same type of resistance training without vibration in order to identify the possible differences due to the vibration itself. Because elderly women are known to be at greater risk of losing functional independence than elderly men (Skelton et al. 1994), this study was performed in a population of post-menopausal women. Material and methods. Eleven postmenopausal, recreationally active women, were assigned either to a vibration training group (VT, n=7, mean \ub1 S.D: age 67.7\ub16.3 years, BMI 23.2\ub12) or to a control training group (CT, n=4, mean \ub1 S.D: age 68.2\ub18.8 years, BMI 30.7\ub15.6). The VT underwent static isometric training on a vibration platform (Galileo Fitness \ua9, Novotec Maschinen GmbH, Germany) 3 times per week for 8 weeks. Each session consisted of four sets of ten isometric semi-squats lasting ten seconds (80\ub0 of knee flexion) on the vibration platform at 30 Hz (amplitude: 0\u20135.2 mm), with ten seconds rest off the platform between each repetition. The CT undertook the same protocol but without vibration. During the workout all participants wore a weighted vest corresponding to 60% of one repetition maximum (1 RM), assessed weekly with a leg extension machine, in order to increase the intensity of the exercise. Quadriceps muscle volume (MV) assessed by magnetic resonance imaging, relative peak power (RP), peak power per muscle volume (PV) and height (JH) assessed during counter-movement jumps performed on a force platform (Leonardo \ua9, Novotec Medical, Pforzheim, Germany), were measured before and after the training periods. Results. Between pre- and post-training VT and CT showed a non significant increase in MV by 3.3 and 4.9%, and in RP by 3.9 and 3.8% respectively (p>0.05). PV did not change in VT and slightly decreased (-2%) in CT in a non significant manner (p>0.05). JH did not show any change. Furthermore, no significant differences were found between the two training groups (p>0.05). Conclusion. The results of this study suggest that whole body vibration, associated with strength training, does not produce greater gains in muscle volume and power than strength training alone. We cannot exclude that with a training period longer than the present one (8 weeks) or targeting an elderly population of older age, greater benefits may be seen. A noteworthy and positive observation is that none of the elderly participants found WBV uncomfortable. Keywords: vibration, training, postmenopausal, muscle volume References Rehn B, Lidstr\uf6m J, Skoglund J, Lindstr\uf6m B. Effects on leg muscular performance from whole-body vibration exercise: a systematic review. Scand J Med Sci Sports 2007; 17: 2\u201311 Skelton DA, Greig CA, Davies JM, Young A. Strength, power and related functional ability of healthy people aged 65\u201389 years. Age Aging 1994; 23: 371\u2013