Altersbedingte änderungen in kontraktilen Eigenschaften der plantar Flexor Muskeln bei physisch aktiven Frauen

Twitch contractile properties of the plantar flexor muscles were compared between the groups of women of the 3rd, 5th, 6th and 8th decade participating in regular recreational physical activity. An isometric twitch was evoked by supramaximal electrical stimulation of the tibial nerve in the popliteal fossa by a rectangular pulse of 1 millisecond duration. A significant decrease was found in the twitch peak force, the maximal rates of force development and relaxation from the 6th decade onwards. A significant prolongation in twitch contraction time was observed from the 5th decade onwards. The 3rd decade group showed a significant postactivation potentiation, while the three older groups did not. No significant age-related changes were observed in the isometric twitch peak force and voluntary strength ratio, and the twitch half-relaxation time in women participating in regular recreational physical activity. It was concluded that the marked decrease in twitch force-potentiation and prolongation of the contraction time of the plantar flexor muscles in physically active women seem to begin after 40 years of age, while a reduction in the maximal voluntary and twitch force-generating capacity, and twitch contraction kinetics occurs after 50 years of age.Uvod Cilj ovog istraživanja bio je izmjeriti učinak starenja na trzajna kontraktilna svojstva skeletnih mišića kod žena uključenih u redovitu rekreacijsku tjelesnu aktivnost. Mjereni su mišići potkoljenice, plantarni fleksori stopala, koji su važni za držanje tijela i kretanje, a aktivni su u mnogobrojnim radnim i sportskim aktivnostima. Metode Ukupno je 49 žena pristalo sudjelovati u ovom istraživanju. Raspoređene su u 4 dobne skupine: skupina u 3. desetljeću života (u dobi od 20 do 25 godina, n=13), skupina u 5. desetljeću života (u dobi od 40 do 49 godina, n=12), skupina u 6. desetljeću života (u dobi od 50 do 59 godina, n=11) i skupina u 8. desetljeću života (u dobi od 70 do 77 godina, n=13). Sve su mlađe ispitanice bile fizički zdrave studentice uključene u redovitu tjelovježbu dva do tri puta tjedno u skupinama odbojke, košarke ili aerobike. Ispitanice srednje dobi vježbale su u skupinama odbojke ili aerobike dva puta tjedno, a starije ispitanice također su vježbale u skupinama aerobike dva puta tjedno. Tijekom mjerenja, ispitanice su sjedile na posebno dizajniranoj stolici, s dominantnom nogom savijenom u koljenom zglobu pod kutom od 90° i smještenom unutar metalnog okvira. Da bi se utvrdila kontraktilna svojstva mišića plantarnih fleksora tijekom izometričkog trzaja, parom samoljepljivih elektroda podraživali smo stražnji tibijalni živac. Katoda je postavljena iznad tibijalnog živca u poplitealnoj jami, a anoda je postavljena ispod stražnje medijalne strane natkoljenice. Izolirani voltažni stimulator bio je izvor supramaksimalnih pravokutnih podražaja od 1 ms. Nakon bilježenja mišićne kontrakcije u mirovanju, ispitanice su dobile uputu da 5 sekundi zadrže mišić u maksimalnoj voljnoj kontrakciji (MVC), a zatim da ga opuste. Drugi (potencirani) trzajni podražaj nastupio je unutar 1 s nakon početka relaksacije. Izračunate su sljedeće karakteristike izometričkog trzaja: vršna sila trzaja (PT) – najveća vrijednost izometričke sile, vrijeme kontrakcije (CT) – vrijeme do vršne sile trzaja, poluvrijeme relaksacije (HRT) – vrijeme polovičnog opadanja vršne sile trzaja, maksimalna brzina razvoja sile (RFD) – prva derivacija razvoja sile (dF/dt) i maksimalna brzina relaksacije (RR) kao prva derivacija opadanja sile (-dF/dt). Postotak porasta potencirane vršne sile trzaja (PT) u odnosu na vrijednost u mirovanju uzet je kao pokazatelj postaktivacijske potencijacije (PAP). Vršna sila trzaja u mirovanju izražena je kao omjer s izometričkom voljnom jakosti. Rezultati Prosječna vrijednost vršne sile trzaja u skupini žena u 3. desetljeću života bila je veća (p<0.05) od prosječnih vrijednosti u skupinama žena u 6. i 8. desetljeću. Skupina u 5. desetljeću pokazala je veću (p<0.05) vršnu silu trzaja od skupine u 8. desetljeću. Razlike u vršnoj sili trzaja između dvije mlađe i dvije starije skupine nisu bile značajne. Među skupinama nisu uočene značajne razlike u omjeru između vršne sile trzaja i voljne jakosti. Uočeno je produljenje vremena kontrakcije (CT) izometričkog trzaja s porastom dobi. Prosječna vrijednost vremena kontrakcije (CT) trzaja u najmlađoj skupini bila je manja (p<0.05) od vrijednosti triju starijih skupina. Razlike u CT trzaja između skupina u 5., 6. i 8. desetljeću nisu bile značajne. Nije bilo značajnih razlika među izmjerenim dobnim skupinama u prosječnim vrijednostima poluvremena relaksacije (HRT) trzaja. Vrijednosti maksimalne RFD i RR izometričkog trzaja smanjile su se s dobi. Vrijednost aritmetičke sredine maksimalne brzine razvoja sile trzaja (RFD) u skupini u 3. desetljeću bila je veća (p<0.05) od vrijednosti u skupinama žena u 6. i 8. desetljeću. Razlike u maksimalnoj RFD trzaja između dviju mlađih i dviju starijih skupina nisu bile značajne. Prosječna vrijednost maksimalne brzine relaksacije (RR) trzaja u skupini u 8. desetljeću bila je manja (p<0.05) od vrijednosti u dvije mlađe skupine. Maksimalna RR trzaja u skupini u 3. desetljeću bila je veća (p<0.05) u usporedbi s vrijednosti skupine u 6. desetljeću. Razlike u maksimalnoj RR trzaja između dvije mlađe skupine i dvije starije skupine nisu bile značajne. Nisu uočene značajne razlike u RR trzaja u usporedbi skupina u 6. i 5. desetljeću. Postaktivacijska potencijacija (PAP) bila je značajno izražena (p<0.05) samo u najmlađoj skupini, dok za tri starije skupine postaktivacijska potencijacija nije bila značajna. Skupina u 3. desetljeću imala je veće vrijednosti (p<0.05) PAP od skupine u 8. desetljeću, dok razlike u PAP između skupina u 3., 5. i 6. desetljeću nisu bile značajne. Vrijednost PAP u skupini u 8. desetljeću nije se značajno razlikovala od vrijednosti PAP u skupinama u 5. i 6. desetljeću. Rasprava i zaključak Ovo je istraživanje pokazalo da je značajno, s dobi povezano opadanje izometričkog maksimalnog voljnog i električno izazvanog kapaciteta stvaranja sile trzaja, kao i opadanje kinetike trzajne kontrakcije, ocijenjeno brzinama razvoja sile i relaksacije mišića plantarnih fleksora stopala, kod žena uključenih u redovitu tjelesnu aktivnost započelo nakon 50. godine. Suprotno prijašnjim istraživanjima, nisu uočene značajne promjene povezane s dobi u omjeru između vršne sile trzaja i voljne jakosti ni u poluvremenu relaksacije trzaja kod žena uključenih u redovitu rekreacijsku tjelesnu aktivnost. Mehanizmi odgovorni za trzajnu potencijaciju nakon kratke izometričke maksimalne voljne kontrakcije značajno su pod utjecajem starenja. Opadanje kapaciteta trzajne potencijacije i produljenje vremena kontrakcije mišića plantarnih fleksora stopala kod tjelesno aktivnih žena započelo je nakon 40. godine.Einzelkontraktile Eigenschaften von M. triceps surae wurden zwischen den Frauengruppen der 3., 5., 6. und 8. Lebensdekade, die regelmäßig physisch aktiv waren, verglichen. Die isometrische Einzelkontraktion wurde mit supramaximaler elektrischer Stimulation des N. tibialis in der Fossa Poplitea bei Rechteckim-pulse von 1 ms Dauerhaftigkeit erreicht. Der wesentliche Fall der Einzelkontraktion bei Maximalkraft im maximalen Kraftgradient und im Relaxiongradient wurde ab 6. Dekade und die Erscheinung der Kontrak-tionszeitverlängerung ab 5. Dekade gefunden. Bei der Gruppe der 3. Dekade erschien die wesentliche post-aktive Potensierung, bei den 3 älteren Gruppen wurde diese Erscheinung nicht gefunden. Bei körperlich aktiven Frauen wurden keine wesentlichen Alterserscheinungen sowohl bei maximaler Kraft der Einzelkon-traktionen und bei willkürlicher Kraft als auch bei Einzelkontraktion in der Halbentspannungszeit gefunden. Zusammengefasst ergibt sich daraus, dass der wesentliche Fall bei der Fähigkeit des Kraftgenerierens und die Verlängerung der Kontraktionszeit bei physisch aktiven Frauen nach dem 40. Lebensjahr erschienen, wobei der Fall der willkürlichen maximalen Kraft und bei der postaktiven Potensierung der Einzelkontrak-tion erst nach dem 50. Lebensjahr erscheint

Using the split squat to potentiate bilateral and unilateral jump performance

The purpose of this study was to examine if a split squat conditioning exercise with no or light loads could potentiate unilateral and bilateral jump performance. Twelve semi-professional rugby players (age: 22.3 +/- 1.4 years; height: 1.84 +/- 0.05 m, mass: 92.4 +/- 9.6 kg) from the English National League 1 performed a series of unilateral and bilateral countermovement jumps (CMJ) and broad jumps (BJ) over the course of two testing days. Both testing days involved performing baseline jumps before completing two sets of ten repetitions of a split squat, this completed with either bodyweight (testing session 1) or a 30kg weighted vest (testing session 2). A five-minute recovery period was permitted both following the warm up and following the completion of the split squat exercise. Significantly larger bilateral jump scores were reported following completion of the bodyweight split squat: CMJ (p = 0.001, ES = 0.44, [mean difference 2.517]), BJ (p = 0.001, ES = 0.37, [mean difference 3.817]), and the weighted vest split squat; CMJ (p = 0.001, ES = 0.8, [mean difference 4.383]), BJ (p = 0.001, ES = 0.68, [mean difference 6.817]). The findings of this study demonstrate that no or light loads of a split squat conditioning exercise are able to potentiate bilateral jump performance in semi-professional rugby players without the need for expensive weight room equipment. As such, this may provide coaches with a viable option of enhancing bilateral jump performance as part of a warm up or on-field conditioning practice

Asymmetries in explosive strength following anterior cruciate ligament reconstruction

Background: Despite its apparent functional importance, there is a general lack of data regarding the time-related changes in explosive strength and the corresponding side-to-side asymmetries in individuals recovering from an ACL reconstruction (ACLR). The present study was designed to assess changes in the maximum and explosive strength of the quadriceps and hamstring muscles in athletes recovering from an ACLR. Methods: Twenty male athletes with an ACL injury completed a standard isometric testing protocol pre-ACLR, four and six months post-ACLR. In addition to the maximum strength (F-max), the explosive strength of quadriceps and hamstrings was assessed through four variables derived from the slope of the force-time curves over various time intervals (REDmax, RED50, RFD150 and RED250). Side-to-side asymmetries were calculated relative to post-ACLR measures of the uninvolved leg ("standard" asymmetries), and relative to pre-ACLR value of the uninvolved leg ("real" asymmetries). Results: Pre-ACLR asymmetries in quadriceps RFD (average 26%) were already larger than in F-max (14%) (p lt 0.05). Six months post-ACLR real asymmetries in RFD variables (33-39%) were larger than the corresponding standard asymmetries (26-28%; p lt 0.01). Average asymmetries in hamstrings' RFD and F-max were 10%, 25% and 15% for pre-ACLR and two post-ACLR sessions, respectively (all p gt 0.05). Conclusions: In addition to the maximum strength, the indices of explosive strength should also be included in monitoring recovery of muscle function following an ACLR. Furthermore, pre-injury/reconstruction values should be used for the post-ACLR side-to-side comparisons, providing a more valid criterion regarding the muscle recovery and readiness for a return to sports

Between-day reliability of electromechanical delay of selected neck muscles during performance of maximal isometric efforts

<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to assess the between-day reliability of the electromechanical delay (EMD) of selected neck muscles during the performance of maximal isometric contractions in five different directions.</p> <p>Methods</p> <p>Twenty-one physically active males participated in two testing sessions separated by seven to eight days. Using a custom-made fixed frame dynamometer, cervical force and surface electromyography (EMG) were recorded bilaterally from the splenius capitis, upper trapezius and sternocleidomastoid muscles during the performance of efforts in extension, flexion, left and right lateral bending, and protraction. The EMD was extracted using the Teager-Kaiser Energy Operator. Reliability indices calculated for each muscle in each testing direction were: the difference in scores between the two testing sessions and corresponding 95% confidence intervals, the standard error of measurement (SEM) and intra-class correlation coefficients (ICC).</p> <p>Results</p> <p>EMD values showed no evidence of systematic difference between the two testing sessions across all muscles and testing directions. The SEM for extension, flexion and lateral bending efforts ranged between 2.5 ms to 4.8 ms, indicating a good level of measurement precision. For protraction, SEM values were higher and considered to be imprecise for research and clinical purposes. ICC values for all muscles across all testing directions ranged from 0.23 to 0.79.</p> <p>Conclusion</p> <p>EMD of selected neck muscles can be measured with sufficient precision for the assessment of neck muscle function in an athletic population in the majority of directions tested.</p

Antisense PMO cocktails effectively skip dystrophin exons 45-55 in myotubes transdifferentiated from DMD patient fibroblasts

Antisense-mediated exon skipping has made significant progress as a therapeutic platform in recent years, especially in the case of Duchenne muscular dystrophy (DMD). Despite FDA approval of eteplirsen-the first-ever antisense drug clinically marketed for DMD-exon skipping therapy still faces the significant hurdles of limited applicability and unknown truncated protein function. In-frame exon skipping of dystrophin exons 45-55 represents a significant approach to treating DMD, as a large proportion of patients harbor mutations within this "hotspot" region. Additionally, patients harboring dystrophin exons 45-55 deletion mutations are reported to have exceptionally mild to asymptomatic phenotypes. Here, we demonstrate that a cocktail of phosphorodiamidate morpholino oligomers can effectively skip dystrophin exons 45-55 in vitro in myotubes transdifferentiated from DMD patient fibroblast cells. This is the first report of substantive exons 45-55 skipping in DMD patient cells. These findings help validate the use of transdifferentiated patient fibroblast cells as a suitable cell model for dystrophin exon skipping assays and further emphasize the feasibility of dystrophin exons 45-55 skipping in patients

Exercise therapy for prevention of falls in people with Parkinson's disease: A protocol for a randomised controlled trial and economic evaluation

<p>Abstract</p> <p>Background</p> <p>People with Parkinson's disease are twice as likely to be recurrent fallers compared to other older people. As these falls have devastating consequences, there is an urgent need to identify and test innovative interventions with the potential to reduce falls in people with Parkinson's disease. The main objective of this randomised controlled trial is to determine whether fall rates can be reduced in people with Parkinson's disease using exercise targeting three potentially remediable risk factors for falls (reduced balance, reduced leg muscle strength and freezing of gait). In addition we will establish the cost effectiveness of the exercise program from the health provider's perspective.</p> <p>Methods/Design</p> <p>230 community-dwelling participants with idiopathic Parkinson's disease will be recruited. Eligible participants will also have a history of falls or be identified as being at risk of falls on assessment. Participants will be randomly allocated to a usual-care control group or an intervention group which will undertake weight-bearing balance and strengthening exercises and use cueing strategies to address freezing of gait. The intervention group will choose between the home-based or support group-based mode of the program. Participants in both groups will receive standardized falls prevention advice. The primary outcome measure will be fall rates. Participants will record falls and medical interventions in a diary for the duration of the 6-month intervention period. Secondary measures include the Parkinson's Disease Falls Risk Score, maximal leg muscle strength, standing balance, the Short Physical Performance Battery, freezing of gait, health and well being, habitual physical activity and positive and negative affect schedule.</p> <p>Discussion</p> <p>No adequately powered studies have investigated exercise interventions aimed at reducing falls in people with Parkinson's disease. This trial will determine the effectiveness of the exercise intervention in reducing falls and its cost effectiveness. This pragmatic program, if found to be effective, has the potential to be implemented within existing community services.</p> <p>Trial registration</p> <p>The protocol for this study is registered with the Australian New Zealand Clinical Trials Registry (ACTRN12608000303347).</p

Changes in muscle contractile characteristics and jump height following 24 days of unilateral lower limb suspension

We measured changes in maximal voluntary and electrically evoked torque and rate of torque development because of limb unloading. We investigated whether these changes during single joint isometric muscle contractions were related to changes in jump performance involving dynamic muscle contractions and several joints. Six healthy male subjects (21 ± 1 years) underwent 3 weeks of unilateral lower limb suspension (ULLS) of the right limb. Plantar flexor and knee extensor maximal voluntary contraction (MVC) torque and maximal rate of torque development (MRTD), voluntary activation, and maximal triplet torque (thigh; 3 pulses at 300 Hz) were measured next to squat jump height before and after ULLS. MVC of plantar flexors and knee extensors (MVCke) and triplet torque decreased by 12% (P = 0.012), 21% (P = 0.001) and 11% (P = 0.016), respectively. Voluntary activation did not change (P = 0.192). Absolute MRTD during voluntary contractions decreased for plantar flexors (by 17%, P = 0.027) but not for knee extensors (P = 0.154). Absolute triplet MRTD decreased by 17% (P = 0.048). The reduction in MRTD disappeared following normalization to MVC. Jump height with the previously unloaded leg decreased significantly by 28%. No significant relationships were found between any muscle variable and jump height (r < 0.48), but decreases in torque were (triplet, r = 0.83, P = 0.04) or tended to be (MVCke r = 0.71, P = 0.11) related to decreases in jump height. Thus, reductions in isometric muscle torque following 3 weeks of limb unloading were significantly related to decreases in the more complex jump task, although torque in itself (without intervention) was not related to jump performance