Métodos de entrenamiento de fuerza alternativos para incrementar la activación muscular en ejercicios de empuje

Introducción. Los movimientos en los que se empuja o presiona con los brazos a una resistencia externa constituyen un elemento clásico dentro de los programas de entrenamiento de la fuerza. Tradicionalmente se han empleado ejercicios convencionales con pesos libres y máquinas con los que se conseguía alcanzar intensidades de activación muscular altas. Sin embargo, tratando de incrementar en mayor medida la intensidad en este tipo de ejercicios, durante los últimos años se han comenzado a utilizar nuevos medios y métodos alternativos (por ejemplo utilizando dispositivos de suspensión, resistencia elástica o tratando de activar músculos de forma selectiva). No obstante, es escasa la evidencia científica que avala dichos recursos materiales y métodos alternativos para incrementar la activación muscular en extremidades superiores y tronco al compararlos con métodos más tradicionales. Los objetivos de la presente tesis fueron: 1) Comparar la activación muscular al realizar flexiones suspendidas con cuatro elementos de suspensión diferentes (Artículo I). 2) Evaluar la activación muscular durante diferentes variaciones de flexiones de brazos y comparar su activación con la del press de banca y el press polea en bipedestación, ambos realizados al 50%, 70% y 85% de 1 repetición máxima (RM) (Artículo II). 3) Evaluar la activación muscular en 6RM de press de banca y en 6RM de flexiones de brazos en el suelo realizadas con resistencia elástica añadida y a continuación evaluar las ganancias de fuerza tras utilizar un ejercicio u otro (Artículo III). 4) Evaluar si al focalizarse en el pectoral mayor o el tríceps braquial durante el press de banca se puede incrementar la activación de forma selectiva. Se presta especial atención a la relación entre la intensidad del ejercicio y la magnitud de la activación selectiva (Artículo IV). Métodos. Para investigar el primer objetivo de la tesis (Artículo I), 29 varones, estudiantes universitarios sanos participaron de manera voluntaria realizando 3 flexiones de brazos con cada uno de los 4 dispositivos de suspensión. La velocidad del ejercicio fue controlada utilizando un metrónomo y el orden de los ejercicios fue aleatorio. Los niveles de activación muscular fueron adquiridos utilizando electromiografía (EMG) en la porción larga del tríceps braquial, trapecio porción superior, porción anterior del deltoides, porción clavicular del pectoral mayor, recto anterior del abdomen, recto femoral y erector lumbar espinal. Para investigar el segundo objetivo (Artículo II), 29 varones, estudiantes universitarios y sanos participaron de manera voluntaria realizando 3 repeticiones en todas las condiciones bajo los mismos procedimientos estandarizados. Se analizó la señal de EMG de los músculos recto anterior del abdomen, oblícuo externo, porción esternocostal del pectoral mayor, porción anterior del deltoides, porción larga del tríceps braquial, trapecio porción superior, serrato anterior y la porción posterior del deltoides. Para abordar el tercer objetivo de la presente tesis (Artículo III), 30 estudiantes universitarios con experiencia de entrenamiento de fuerza participaron voluntariamente en un estudio de dos partes. Cada sujeto participó en 16 sesiones diferentes realizadas en el siguiente orden: dos sesiones de familiarización, evaluación de 1RM en el press de banca, dos test de 6RM con evaluación de EMG en la porción esternocostal del pectoral mayor y la porción anterior del deltoides, 10 sesiones de entrenamiento durante 5 semanas (usando las mismas cargas y variables que fueron usadas durante la evaluación EMG), medición de 1RM y 6RM en press de banca. Por último, un total de 18 adultos hombres con experiencia de entrenamiento de fuerza participaron voluntariamente para evaluar el cuarto objetivo de la tesis (Artículo IV). Los sujetos realizaron 3 repeticiones en 3 diferentes condiciones de press de banca (press de banca tradicional y press de banca tratando de utilizar de forma selectiva los músculos pectoral mayor o tríceps braquial) a intensidades del 20%, 40%, 50%, 60% y 80% de 1RM. Se evaluó la señal de EMG de los músculos mencionados. Resultados y conclusiones. En el Artículo I, las flexiones suspendidas con el dispositivo con polea generaron mayor actividad en el tríceps braquial, el trapecio porción superior, el recto femoral y el erector lumbar espinal que el resto de dispositivos de suspensión y que las flexiones tradicionales. El dispositivo con dos anclajes generó mayor activación del pectoral mayor que el resto de dispositivos y las flexiones tradicionales. Sin embargo, las flexiones tradicionales proporcionaron mayor activación muscular de la porción anterior del deltoides que el resto de dispositivos de suspensión, exceptuando el de dos anclajes. Todos los dispositivos de suspensión incrementaron de forma efectiva la activación muscular en el recto anterior del abdomen. En el Artículo II, las flexiones realizadas con resistencia elástica generaron similar activación muscular en los principales movilizadores que el press de banca realizado a alta intensidad, mientras que generaron mayor activación en la musculatura abdominal. Las flexiones suspendidas fueron muy efectivas para estimular la musculatura abdominal. La activación del pectoral mayor, porción anterior del deltoides y serrato anterior fue mayor durante condiciones más estables, mientras que los músculos del abdomen, el tríceps braquial y la porción posterior del deltoides se activaron más durante los ejercicios realizados en situación de inestabilidad. En el Artículo III, 6RM en press de banca y 6RM en flexiones con resistencia elástica generaron comparables valores de EMG durante la sesión de evaluación y también provocaron ganancias de fuerza similares después del periodo de intervención, mientras que el grupo control permaneció igual. Así, cuando los niveles de activación muscular son comparables y los ejercicios de empuje sean biomecánicamente y cinemáticamente similares, las ganancias de fuerza serán similares. En el Artículo IV, sujetos con experiencia de entrenamiento de fuerza fueron capaces de incrementar la activación del tríceps braquial o el pectoral mayor cuando se focalizaban en uno u otro músculo durante el press de banca realizado hasta intensidades del 60% de 1RM. Parece existir un umbral entre 60% y 80% de 1RM. En conclusión, existen cantidad de alternativas a los métodos convencionales para alcanzar niveles altos de actividad muscular (y por tanto ganancias de fuerza). Ello proporciona un mayor grado de variación en ejercicios para incrementar la fuerza muscular de lo que se pensaba.Introduction. Pushing or pressing movements with the arms against external resistance are classic elements of strength training programs. Traditionally, conventional strength exercises using free weights and machines have been used for achieving high intensities of muscle activity. However, new ways and alternative training methods (e.g. by using suspension training devices, elastic resistance or trying to selectively activate muscles) have increased during recent years. Nevertheless, scientific evidence supporting the use of such training methods and devices to achieve high intensities of upper-body muscle activity is scarce. The main purposes of this PhD thesis were: 1. To compare muscle activity during suspended push-ups using different suspension training systems (Paper I). 2. To compare muscle activity during push-up variations with the bench press exercise and the standing cable press exercise both performed at 50%, 70%, and 85% of the 1-repetition maximum (Paper II). 3. To compare muscle activity during 6 repetition maximum (6RM) bench press and added-resistance push-up, and subsequently to evaluate the strength gains after a training period with each of these exercises (Paper III). 4. To evaluate whether focusing on using the pectoralis major and triceps brachii muscles, respectively, during bench press can selectively activate these muscles. We were especially interested in measuring the relationship between exercise intensity and the magnitude of selective activation (Paper IV). Methods. To investigate the first purpose of the thesis (Paper I), 29 fit male university students voluntarily participated performing 3 push-ups each with 4 different suspension systems. Push-up speed was controlled using a metronome. Testing order was randomized. The level of muscle activity was recorded using electromyography (EMG) for the triceps brachii, upper trapezius, anterior deltoid, clavicular pectoralis, rectus abdominis, rectus femoris, and lumbar erector spinae. To investigate the second purpose (Paper II), 29 fit male students voluntarily participated performing 3 repetitions in all conditions under the same standardized procedures. EMG signals were recorded for the rectus abdominis, external oblique, sternocostal head of the pectoralis major, anterior deltoid, long head of the triceps brachii, upper trapezius, anterior serratus and posterior deltoid. To address the third aim of the present thesis (Paper III), 30 university students with resistance training experience voluntarily participated in a two-part study. Each participant took part in 16 sessions in the following order: two familiarization sessions, a 1RM bench press test session, two 6RM tests with EMG data collection on the sternocostal head of the pectoralis major and anterior deltoid, 10 training sessions during 5 weeks (using the same loads and variables that were used during the EMG data collection), a post-1RM bench press estimation session, and lastly a post-6RM bench press estimation session. Finally, to evaluate the fourth purpose of this thesis, 18 resistance-trained adult men voluntarily participated. Subjects performed 3 repetitions on 3 different bench press conditions with intensities of 20%, 40%, 50%, 60% and 80% of 1RM: regular bench press, and bench press focusing on selectively using the pectoralis major and triceps brachii, respectively. EMG signals were recorded for the triceps brachii and pectoralis major muscles. Results and conclusions. In Paper I, the suspended push-up with a pulley system provided greater triceps brachii, upper trapezius, rectus femoris and lumbar erector spinae muscle activity compared with the other suspension systems and the standard push-up. The twoanchor system provided greater pectoralis major activity than the other systems and the standard push-up. However, the standard push-up provided greater anterior deltoid activity than the other suspension systems except the two-anchor system. All the suspension systems effectively enhanced rectus abdominis activity.In Paper II, elastic-resisted push-ups induced similar levels of muscle activity the prime movers as the bench press performed at high load while also providing a greater core activity. Suspended push-ups were highly effective to induce high levels of abdominal muscle activity. Muscle activity of the pectoralis major, anterior deltoid and anterior serratus were higher during more stable pushing conditions, whereas abdominal muscles, triceps brachii, posterior deltoid and upper trapezius were more active during the unstable exercises. In Paper III, the 6RM bench press and the 6RM elastic-resisted push-ups induced comparable levels of muscle activity as assessed by EMG during the baseline session, and provided comparable muscle strength gains after the intervention period, whereas control group remained unchanged. Thus, when the levels of muscle activity are comparable and the kinematics and biomechanics of the push exercises are broadly similar, the gain in muscle strength will be similar. In Paper IV, resistance-trained participants were able to increase triceps brachii or pectoralis major muscle activity during the bench press when focusing on using either of these specific muscle at intensities up to 60% of 1RM. A threshold between 60% and 80% where selective activity no longer was possible appeared to exist. In conclusion, several alternatives to conventional methods for reaching high levels of muscle activity – and thus strength gains – appear to exist. This provides a larger degree of variability for exercises to increase muscle strength than previously thought

Focusing on increasing velocity during heavy resistance knee flexion exercise boosts hamstring muscle activity in chronic stroke patients

Background. Muscle strength is markedly reduced in stroke patients, which has negative implications for functional capacity and work ability. Different types of feedback during strength training exercises may alter neuromuscular activity and functional gains. Objective. To compare levels of muscle activity during conditions of blindfolding and intended high contraction speed with a normal condition of high-intensity knee flexions. Methods. Eighteen patients performed unilateral machine knee flexions with a 10-repetition maximum load. Surface electromyography (EMG) was recorded from the quadrics and hamstring muscles and normalized to maximal EMG (nEMG) of the nonparetic limb. Results. For the paretic leg, the speed condition showed higher values of muscle activity compared with the normal and blindfolded conditions for both biceps femoris and semitendinosus. Likewise, the speed condition showed higher co-contraction values compared with the normal and blindfolded conditions for the vastus lateralis. No differences were observed between exercise conditions for the nonparetic leg. Conclusion. Chronic stroke patients are capable of performing heavy resistance training with intended high speed of contraction. Focusing on speed during the concentric phase elicited higher levels of muscle activity of the hamstrings compared to normal and blindfolded conditions, which may have implications for regaining fast muscle strength in stroke survivors

Association of Stress and Musculoskeletal Pain With Poor Sleep: Cross-Sectional Study Among 3,600 Hospital Workers

Background: While acute stress and pain are part of our inherent survival mechanisms, persistent stress and pain can negatively impact health and well-being. This may also lead to poor sleep and thus a lack of recovery. This study investigated the influence of stress and musculoskeletal pain on sleep quality.Methods: A total of 3,593 Danish hospital workers replied to a questionnaire about work and health. Pain intensity was evaluated using subjective values as an average of 9 body parts. Stress was assessed using the full version of Cohen's Perceived Stress scale. Sleep quality was rated using 3 questions on sleep characteristics. Associations between stress and pain (mutually adjusted predictors) and sleep (outcome) were modeled using binary logistic regression controlling for gender, age, education, BMI and smoking.Results: The risk ratio of moderate stress (compared to no/low stress) on poor sleep was 1.27 (CI 1.26–1.29), whereas the risk ratio of high stress on poor sleep was 1.87 (CI 1.83–1.91). Similarly, for pain, the risk ratio of moderate pain (compared to no/low pain) on poor sleep was 1.18 (95% CI 1.16–1.19), whereas the risk ratio of a high pain score on poor sleep was 1.48 (95% CI 1.44–1.52).Conclusion: This study demonstrates that both stress and musculoskeletal pain are associated with poor sleep among hospital workers. Hospital management should consider implementing strategies for preventing stress and musculoskeletal pain to improve the overall health and workability among hospital workers

Applying a menthol pain reliever prior to strength training reduces chronic low back pain and increases functional capacity in overweight or obese older adult

The combined effect of a muscle strength training program with the previous application of a topical menthol gel on the intensity of chronic low back pain (CLP) and the functional capacity of overweight/obese older women was evaluated. A randomized controlled clinical trial with parallel group comparison was conducted. In Phase 1 (12-weeks), 31 women were randomly assigned: (i) a control group that did not change their habits (CG; n = 11); (ii) group of strength training prior to application of a gel with menthol (RTM; n = 10) and (iii) group that performed the same training prior to application of a placebo gel (RTP; n = 10). After 12 weeks of no training, phase 2 of the study (32-week duration) was run, where the RTM and RTP women were randomly reassigned. It was evaluated before and after each phase: body composition, functional capacity, pain perception and Oswestry disability index. The significance level established for the study was p ≤ .05. Both training groups significantly improved all variables after stages 1 and 2, with significant post-intervention differences but no significant intergroup differences, although RTM obtained better results. The percentage of improvement in pain perception and functional parameters were related to the intervention time without positive effects for CG. In conclusion, the use of menthol gel prior to a muscle strength program reduced pain and enhanced the functional improvements achieved as a result of moderate-high intensity training in older adult women with CLP and overweight or obesity

Is hard physical work in the early working life associated with back pain later in life?:A cross-sectional study among 5700 older workers

Objectives Physically demanding work increases the risk of developing musculoskeletal disorders during working life, with low back pain (LBP) as the most prevalent and debilitating musculoskeletal disorder worldwide. However, a lack of knowledge exists about the role of early working years on musculoskeletal health later in life. This study investigated whether an exposure-response association exists between physical demands in early working life and risk of LBP in later working life. Design Cross-sectional study. Setting, participants and outcome measure In the SeniorWorkingLife study, 5909 wage earners aged =50 years with currently sedentary work replied to a questionnaire survey in 2018 about physical work demands during their first working years (exposure) and current LBP (outcome). Associations between physical work demands in the early working years and current LBP were modelled using general linear models controlling for various confounders, combined with model-Assisted weights based on national registers. Results Hard physical work during early working life was associated with more intense LBP later in life among senior workers with currently sedentary jobs. In the fully adjusted model, workers with â standing/walking work with lifting/carrying' and â heavy or fast work that is physically strenuous' during the first years of working life reported higher LBP intensity than those with sedentary work during their first working years (0.2 (95% CI, 0.0 to 0.4) and 0.6 (95% CI, 0.4 to 0.9), respectively). Conclusion Work involving lifting/carrying or work that is physically strenuous in early life is associated with higher intensity of LBP among older workers with currently sedentary employment. These findings suggest that early working life may have an impact on later working years and underscore the necessity for careful introduction and instruction to the working environment for retaining musculoskeletal health and prolonging working life. Trial registration number NCT03634410

Effect of a brief progressive resistance training program in hospital porters on pain, work ability, and physical function

Background Hospital porters are possibly exposed to the greatest mechanical loads within the hospital environment. However, the evidence about preventive strategies in this population is scarce. Objective To investigate the effect of a workplace-based progressive resistance-training program on musculoskeletal pain among hospital porters. Method A total of 37 hospital porters (27 women, 10 men) participated. Participants allocated to the intervention group performed five brief resistance training sessions/week, for 9 weeks during working hours at the hospital. Intensity was progressively increased. Participants allocated to the control group maintained their usual physical activity. The primary outcome was pain assessed with the patient global impression of pain change scale. Secondary outcome measures were average pain intensity, work ability, use of analgesics, and physical function. Additionally, perceived general changes were evaluated at follow-up: wellness, satisfaction at work, desire to exercise, motivation to eat healthy, energy to be with family and friends, and socialization with colleagues. Results For the primary outcome, the intervention group showed lower general pain (p < 0.0001) and greater wellbeing (p < 0.0001), work satisfaction (p = 0.0048), desire for practicing exercise (p = 0.0007), and energy (p = 0.0474) compared with the control group. Significant between-group interactions were found for work impairment due to diseases (d = -1.2), hips/thighs pain (d = 0.7), ankles/feet pain (d = 0.4), the Biering-Sorensen test (d = -0.6) and the push-ups test (d = -2.3) favoring the intervention group. All between-group differences were clinically important. Conclusion A progressive resistance training program performed at the workplace is feasible and effective in reducing musculoskeletal pain and improving work ability and physical function among hospital porters.This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Escriche-Escuder is supported by a predoctoral grant of the University Teaching Training Programme (FPU) of the Ministry of Science, Innovation and Universities of Spain. Grant number: FPU17/00161

Individuals with chronic ankle instability show altered regional activation of the peroneus longus muscle during ankle eversion

Individuals with chronic ankle instability (CAI) present muscular weakness and potential changes in the activation of the peroneus longus muscle, which likely explains the high recurrence of ankle sprains in this population. However, there is conflicting evidence regarding the role of the peroneus longus activity in CAI, possibly due to the limited spatial resolution of the surface electromyography (sEMG) methods (i.e., bipolar sEMG). Recent studies employing high‐density sEMG (HD‐sEMG) have shown that the peroneus longus presents differences in regional activation, however, it is unknown whether this regional activation is maintained under pathological conditions such as CAI. This study aimed to compare the myoelectric activity, using HD‐sEMG, of each peroneus longus compartment (anterior and posterior) between individuals with and without CAI. Eighteen healthy individuals (No‐CAI group) and 18 individuals with CAI were recruited. In both groups, the center of mass (COM) and the sEMG amplitude at each compartment were recorded during ankle eversion at different force levels. For the posterior compartment, the sEMG amplitude of CAI group was significantly lower than the No‐CAI group (mean difference = 5.6% RMS; 95% CI = 3.4–7.6; p = 0.0001). In addition, it was observed a significant main effect for group (F1,32 = 9.608; p = 0.0040) with an anterior displacement of COM for the CAI group. These findings suggest that CAI alters the regional distribution of muscle activity of the peroneus longus during ankle eversion. In practice, altered regional activation may impact strengthening programs, prevention, and rehabilitation of CAI