Muscle damage, repeated bout effect and training induced changes by different eccentric training modalities

Eccentric contraction has been proved to be different from concentric contraction. Lengthening contraction can be performed using isotonic , isokinetic or inertial devices. Aim of the thesis is to describe different eccentric contraction modalities studying main phenomenon related to them. Five studies will be presented to analyze muscle damage, repeated bout effect, training and detraining induced changes. Abstract1 Lengthening contraction is well known to induce muscle injury and it confers protection to a subsequent eccentric session, i.e. repeated bout effect. Dynamic negative action can be performed resisting to an external load (e.g.: isotonic) or using isokinetic device. Aim of the study is to measure muscle damage and repeated bout effect induced by both lengthening exercise modalities. Thirty males were randomly assigned to isokinetic(IK) or isotonic(IT) group and they tested at baseline, immediately after and up to 4 days after 60 supra maximal eccentric contractions. CK activity, strength loss and muscle soreness were taken as indirect markers of muscle damage. Same protocol was repeated after 4 weeks. Compared to baseline, IK and IT resulted in augmented injury symptoms after first bout. Compared to first bout, second bout resulted in significantly lower muscle damage both in IK and IT. After first bout, compared to IK, IT showed increased CK activity (+30±13%), higher strength loss(+40±14%) and greater soreness (+34±8%), p<0,05 for all parameters. After second bout, compared to IK, IT showed similar CK activity (+12±4%, n.s.), higher strength loss (+24±4%, p<0,05) and similar soreness (+10%±5%, n.s.). Both IK and IT induced muscle damage after first bout. Second bout resulted in less damage for both IK and IT. IT induced significantly greater damage compared to IK, but it confers more protection after second bout. It is concluded that neural and mechanical factor influenced difference between IK and IT eccentric induce damage. Abstract2 Eccentric (ECC) training has been shown to induce greater effect than concentric training on strength, muscle mass and contra lateral adaptations. The majority of the studies have used isokinetic (IK) devices for investigating the acute and chronic effects of ECC training. However, isotonic (IT) apparatuses are more commonly available in sport setting. Aim of the study was to compare ISOK to ISOT ECC training by assessing the effects on muscle strength and mass. Forty-nine healthy sport science students have been randomly divided in 3 groups: IK, IT, and control group (CG). Both training groups performed 50 ECC repetitions of knee extension at 120% of their maximal strength measured in concentric modality (1RM for IT and peak concentric torque for IK), for a total of 14 times in 7 weeks. Isometric maximal voluntary contraction (MVC), concentric and eccentric strength, 1RM, muscle mass and architectural alterations have been measured pre and post training. Compare to CG, the IK group showed higher 1RM (12%, CI95% 6 to 19%), concentric (15%, 8 to 22%), eccentric (35%, 25 to 45%) and isometric (25%, 18 to 34%) maximal strength (P<0.001). Compare to CG, IT showed higher 1RM (14%, 9 to 20%), concentric (17%, 11 to 24%), eccentric (25%, 16 to 34%) and isometric (22%, 15 to 29%) maximal strength (P<0.001). No differences between ISOK and ISOT were found in 1RM (2%, -3 to 7%), concentric (-2%, -4 to 8%) and isometric (-3%, -8 to 3%) maximal strength. Only eccentric strength was higher in the IK compare to the IT group (8%, 1 to 14%). No differences between groups were found in muscle mass (0.419<P<0.769). Untrained limb improve strength in both training groups. Eccentric training improved muscle peak torque and 1RM in physically active people. Data showed that neural adaptation is the main factor increasing muscle strength, while muscle mass apparently was not strictly related to it. IK and IT showed similar training effects. This study displayed that ECC training induced early strength adaptations. Abstract3 Muscle damage is proved to occur after eccentric training. Moreover, it confers protection to a subsequent session, i.e.: repeated bout effect. Aim of the study is evaluate if lengthening contraction enhanced by inertial flywheel squat will cause symptoms of muscle injury and following protection. Twelve healthy amateurs males performed 100 maximal squat repetitions using inertial device. At baseline, after training and up to 4 days after CK blood concentration, Knee extensors strength, muscle soreness and jump performance were measured as markers of muscle damage. Same protocol was repeated after 3 weeks. Compare to baseline, CK and muscle soreness increase respectively up to 3 and 4 days, while strength loss and jump height were affected only post training. The second bout revealed significant markers decrement. Inertial flywheel squat induce classical symptoms of muscle injury, even if strength loss and performance could be positively influenced by neural patterns. Eccentric overload does protect muscle at least up to 3 weeks. Abstract4 Inertial flywheel squat has been proved to increment strength and muscle mass. Aim of the study is to measure transfer in performance, comparing it with a traditional field training. Forty five healthy males underwent to inertial squat (IS) or weighted squat jump (WSJ) or control group. (CG) Before and after 16 sessions of 60 repetition knee extensors and flexors torque, lower limbs lean mass, quadriceps architecture, jump height, 30m dash, 20m shuttle and changing direction ability were tested. Compare to CG, Knee extensors torque increased similarly in IS and WSJ, while only former improved knee flexors strength. Muscle muscle mass and fascicle length augmented more in IS than WSJ, as well as jump. Similar improvements occurred in 20m shuttle and 30m dash, while changing direction ability improved only in WSJ. These data showed that both IS and WSJ are adequate stimuli to improve strength, and they should be used in sport with a great power development Abstract5 Resistance training is classically performed dynamically using both concentric(CONC) and eccentric(ECC) phases (i.e.: CONC+ECC). However, muscle strength and structure gain has been proved superior when E was enhanced. In addition, when performed unilaterally, force has been shown to improve also in untrained limb. Finally after detraining period, adaptations are often retained. Therefore aim of the study is to compare different exercise methods measuring strength, mass and architecture after training and a short detraining. In addition we want to evaluate contra lateral effect and its time course. Sixty women have been randomly divided in CONC, ECC, CONC+ECC or control group (CONTR). Training groups performed 7 weeks of equivolumetric unilateral knee extension, followed by 4 weeks of detraining. Maximal voluntary concentric, eccentric and isometric contraction, 1RM, muscle mass and muscle architecture were measured at baseline, after training and after detraining period. Measurements were performed on both legs. After training, all groups improved concentric, isometric and 1RM compared to baseline, while eccentric torque was greater only in ECC. Muscle mass showed no increment, while fascicle length, fascicle thickness and pennation angle changed dissimilarly in each group. Untrained leg (UT) showed task related strength improvement, without affecting muscle mass, but with changes in muscle architecture. After 4 weeks, strength continued to increase in both in trained and UT, muscle mass was higher only in ECC, while muscle architecture showed further adaptations.