In Cardiac Patients ß-Blockers Attenuate the Decrease in Work Rate during Exercise at a Constant Submaximal Heart Rate.

PURPOSE: Exercise prescription based on fixed heart rate (HR) values is not associated with a specific work rate (WR) during prolonged exercise. This phenomenon has never been evaluated in cardiac patients and might be associated with a slow component of HR kinetics and ß-adrenergic activity. The aims were to quantify, in cardiac patients, the WR decrease at a fixed HR and to test if it would be attenuated by ß-blockers. METHODS: Seventeen patients with coronary artery disease in stable conditions (69 ± 9 yr) were divided into two groups according to the presence (BB) or absence (no-BB) of a therapy with ß-blockers, and performed on a cycle ergometer: an incremental exercise (INCR) and a 15-min "HR CLAMPED " exercise, in which WR was continuously adjusted to maintain a constant HR, corresponding to the gas exchange threshold +15%. HR was determined by the ECG signal, and pulmonary gas exchange was assessed breath-by-breath. RESULTS: During INCR, HR peak was lower in BB versus no-BB ( P < 0.05), whereas no differences were observed for other variables. During HR CLAMPED , the decrease in WR needed to maintain HR constant was less pronounced in BB versus no-BB (-16% ± 10% vs -27 ± 10, P = 0.04) and was accompanied by a decreased V̇O 2 only in no-BB (-13% ± 6%, P < 0.001). CONCLUSIONS: The decrease in WR during a 15-min exercise at a fixed HR (slightly higher than that at gas exchange threshold) was attenuated in BB, suggesting a potential role by ß-adrenergic stimulation. The phenomenon may represent, also in this population, a sign of impaired exercise tolerance and interferes with aerobic exercise prescription.

Effects of 12-week combined training versus high intensity interval training on cardiorespiratory fitness, body composition and fat metabolism in obese male adults.

Background: /Objectives: A weekly combination of a high volume of moderate-intensity continuous training (MICT) with a low volume of high-intensity interval training (HIIT) provides important improvements in body composition and physical capacities in individuals with obesity. However, previous studies did not determine the weekly proportions of HIIT and MICT a priori. This study aimed to investigate changes in body composition, physical capacities and the fat oxidation rate in obese male adults by comparing a combination of MICT and HIIT, called combined training (COMB), with HIIT for a 12-week period. Methods: Thirty-four obese male adults (mean age: 39.4 ± 7.0 y; mean body mass index [BMI] 34.0 ± 4.2 kg m-2) participated in this study (n = 18 for COMB, n = 16 HIIT), attending âˆ¼ 36 training sessions. The COMB group performed 3 repetitions of 2 min at 95% of peak oxygen uptake (V'O2 peak) (e.g., HIIT ≤20%), followed by 30 min at 60% of VO2 peak (e.g., MICT ≥80%). The HIIT group performed 5-7 repetitions of 2 min at 95% of VO2 peak. At baseline (PRE) and at the end of the training period (POST), body composition, VO2 peak, and the fat oxidation rate were measured. The two training programs were equivalent in caloric expenditure. Results: At POST, body mass (BM) and fat mass (FM) decreased by a mean of 3.09 ± 3.21 kg and 3.90 ± 2.40 kg, respectively (P < 0.05), in both groups and V'O2 peak increased in both groups by a mean of 0.47 ± 0.34 L min-1 (P < 0.05). The maximal fat oxidation rate increased similarly in both groups from 0.32 ± 0.05 to 0.36 ± 0.06 g min-1 (P < 0.05). Conclusion: COMB training represents a viable alternative to HIIT to improve anthropometric characteristics, physical capacities and fat oxidation in obese male adults.

Effects of NMES-elicited versus voluntary low-level conditioning contractions on explosive knee extensions.

OBJECTIVES: Electrically-induced or voluntary conditioning-contractions (CC) can be used to affect contractile properties of a subsequent explosive contraction (EC). Here, we aimed at comparing the effect of neuromuscular-electrical-stimulation (NMES) vs voluntary CC performed prior to explosive contractions of the knee extensors. METHODS: A 10 sec NMES CC (100Hz, 1000µs, 10% MVC), or a voluntary contraction (VOL CC) mimicking the NMES CC, preceded an isometric EC of the knee extensors. Explosive contraction was performed with the goal to reach the target (70% MVC) as quickly as possible. RESULTS: All the parameters related with the explosive contractions' muscle-output were similar between protocols (difference ranging from 0.23%, Mean Torque; to 5.8%, Time to Target), except for the Time to Peak Torque, which was lower when preceded by NMES (11.1%, p=0.019). Interestingly, the RTD 0-50 ms_EC was 37.3% higher after the NMES compared with the VOL CC protocol. CONCLUSION: Explosive contraction was potentiated by an NMES CC as compared with a voluntary CC. This may be due to a reduction in descending drive following VOL CC, which has been shown to occur even with low-level voluntary efforts. These findings could be used to improve rehabilitation or training protocols that include conditioning contractions.

Effects of gravitational versus iso-inertial resistance training on leg muscle force and metabolic cost of walking in healthy older adults.

BACKGROUND: The purpose was to compare the effects of 8-week resistance training programs (flywheel iso-inertial [FW] versus traditional gravity-dependent resistance training [GD]) performed twice a week at the same rate of perceived exertion (RPE), on muscle force and power capacities and physical performance in healthy older participants. METHODS: Twenty-four participants were randomly assigned to either FW (male/female ratio: 7/5, age: 67.1±3.8 years) or GD (male/female ratio: 6/6, age 68.3±3.0 years) group. Knee extension maximal isometric voluntary contractions (MVC), lower limb maximal explosive power (MEP), Six-Minute Walking Test (6MWT), Timed Up-and-Go Test (TUG), metabolic cost of walking (CW) and agonist-antagonist co-contraction time (CCT) during walking were evaluated before and after training. RESULTS: absolute MEP and MEP normalized for body mass increased only in FW than GD group (+10.8% vs. +0.31%, P=0.056, respectively; +14.8% vs. +13.9%, P<0.001, respectively). Both training modalities improved MVC to a similar extent (+11.1% in FW vs. +13.4% in GD, P<0.001). Analogously, 6MWT distance increased in FW and GD (+5.2 and +5.5%, P<0.041, respectively). No effects of time and training modality were observed on the other parameters. CONCLUSIONS: The results of this study suggest that when FW and GD are administered at the same RPE with FW performed at higher movement speed in the concentric phase, both the trainings generate similar improvements in muscle strength but only the former can promote greater muscle power enhancements than GD in healthy older adults.

Physical capacities and leisure activities are related with cognitive functions in older adults.

BACKGROUND: This study aimed to evaluate the relationship between physical activity habits, physical performance and cognitive capacity in older adults' population of Italy and Slovenia. METHODS: Anthropometric characteristics and body composition bioelectrical impedance analysis were evaluated in 892 older adults (60-80 y). Aerobic capacity was measured using the 2-km walk test and handgrip and flexibility tests were performed. Physical activity habits and cognitive functions were evaluated by the Global-Physical-Activity-Questionnaires (GPAQ) and by Montreal-Cognitive-Assessment (MoCA) questionnaires, respectively. RESULTS: GPAQ scores were associated with lower BMI (r=-0.096; P=0.005), lower percentage of fat-mass (r=-0.138; P=0.001), better results in the 2-km walk test (r=-0.175; P=0.001) and a higher percentage of fat-free mass (r=0.138; P=0.001). We also evaluated that a higher MoCA Score correlates with age (r=-0.208; P=0.001), 2-km walk test (r=-0.166; P=0.001), waist-hip ratio (r=-0.200; P=0.001), resting heart-rate (r=-0.087; P=0.025) and heart-rate at the end of 2-km walk test (r=0.189; P=0.001). CONCLUSIONS: Older adults with a higher level of daily physical activity showed reduction in fat-mass and BMI, and higher aerobic fitness; these characteristics have a protection effect on cognitive function.

Peripheral Alterations Affect the Loss in Force after a Treadmill Downhill Run.

Downhill running has an important effect on performance in trail running competitions, but it is less studied than uphill running. The purpose of this study was to investigate the cardiorespiratory response during 15 min of downhill running (DR) and to evaluate the neuromuscular consequences in a group of trail runners. Before and after a 15-min DR trial (slope: -25%) at ~60% of maximal oxygen consumption (V̇O2max), we evaluated maximal voluntary contraction torque (MVCt) and muscle contractility in a group of seventeen trail running athletes. Additionally, during the DR trial, we measured V̇O2 and heart rate (HR). V̇O2 and HR increased as a function of time, reaching +19.8 ± 15.9% (p < 0.001; ES: 0.49, medium) and +15.3 ± 9.9% (p < 0.001; ES: 0.55, large), respectively, in the last minute of DR. Post-exercise, the MVCt decreased (-22.2 ± 12.0%; p < 0.001; ES = 0.55, large) with respect to the pre-exercise value. All the parameters related to muscle contractility were impaired after DR: the torque evoked by a potentiated high frequency doublet decreased (-28.5 ± 12.7%; p < 0.001; ES: 0.61, large), as did the torque response from the single-pulse stimulation (St, -41.6 ± 13.6%; p < 0.001; ES: 0.70, large) and the M-wave (-11.8 ± 12.1%; p < 0.001; ES: 0.22, small). We found that after 15 min of DR, athletes had a decreased MVCt, which was ascribed mainly to peripheral rather than central alterations. Additionally, during low-intensity DR exercise, muscle fatigue and exercise-induced muscle damage may contribute to the development of O2 and HR drift.

Effects of NMES pulse width and intensity on muscle mechanical output and oxygen extraction in able-bodied and paraplegic individuals.

PURPOSE: Neuromuscular Electrical Stimulation (NMES) is commonly used in neuromuscular rehabilitation protocols, and its parameters selection substantially affects the characteristics of muscle activation. Here, we investigated the effects of short pulse width (200 µs) and higher intensity (short-high) NMES or long pulse width (1000 µs) and lower intensity (long-low) NMES on muscle mechanical output and fractional oxygen extraction. Muscle contractions were elicited with 100 Hz stimulation frequency, and the initial torque output was matched by adjusting stimulation intensity. METHODS: Fourteen able-bodied and six spinal cord-injured (SCI) individuals participated in the study. The NMES protocol (75 isometric contractions, 1-s on-3-s off) targeting the knee extensors was performed with long-low or short-high NMES applied over the midline between anterior superior iliac spine and patella protrusion in two different days. Muscle work was estimated by torque-time integral, contractile properties by rate of torque development and half-relaxation time, and vastus lateralis fractional oxygen extraction was assessed by Near-Infrared Spectroscopy (NIRS). RESULTS: Torque-time integral elicited by the two NMES paradigms was similar throughout the stimulation protocol, with differences ranging between 1.4% (p = 0.877; able-bodied, mid-part of the protocol) and 9.9% (p = 0.147; SCI, mid-part of the protocol). Contractile properties were also comparable in the two NMES paradigms. However, long-low NMES resulted in higher fractional oxygen extraction in able-bodied (+ 36%; p = 0.006). CONCLUSION: Long-low and short-high NMES recruited quadriceps femoris motor units that demonstrated similar contractile and fatigability properties. However, long-low NMES conceivably resulted in the preferential recruitment of vastus lateralis muscle fibers as detected by NIRS.

Neuromuscular Fatigue of Cycling Exercise in Hypoxia.

INTRODUCTION: The understanding of fatigue in hypoxia is limited due to: lack of control in arterial saturation, different exercise intensities and hypoxia levels, lag time between exercise cessation and fatigue evaluation. We aimed at evaluating fatigue during cycling and immediately after exhaustion (EXH) in normoxia, moderate and severe hypoxia at relative and absolute intensities. METHODS: Thirteen subjects completed three sessions in normoxia, moderate, and severe hypoxia with intensity based on percentage of normoxic maximal power output (NOR, MODABS, SEVABS) plus two sessions where intensity was based on the corresponding environmental condition (MODREL, SEVREL). Arterial saturation was clamped at 85% and 70% in moderate and severe hypoxia, respectively. Before, during cycling, and at EXH, maximum voluntary contraction (MVC), peripheral fatigue (high-frequency doublet [Db100], twitch [Pt]), and central fatigue (cortical voluntary activation [VATMS]) were evaluated without delay using an innovative ergometer. RESULTS: Time to EXH declined not only with hypoxia level at absolute but also relative intensities compared to NOR. At isotime, MVC, Pt, and Db100 were similarly depreciated in NOR, MODREL, and SEVREL. At EXH, there was a similar reduction among conditions in MVC (-26% to -31%), Db100 (-25% to -35%) and VATMS (-9% to -13%). However, Pt was less decreased in SEVREL compared with NOR (-33% ± 17% vs -46% ± 16%). CONCLUSIONS: The shorter time to EXH in relative hypoxia and yet lower peripheral fatigue and similar central fatigue compared with normoxia suggests that hypoxia per se may affect brain areas not directly implicated in quadriceps motor function.

Metabolic and muscular factors limiting aerobic exercise in obese subjects.

PURPOSE: The aim of the present study was to understand the role of central (cardiovascular O2 delivery) and peripheral factors (muscle level) in limiting the maximal aerobic performance in obese (OB) subjects. METHODS: Fifteen OB (mean age ± SD 25 ± 7 years; BMI 43 ± 7 kg/m2) and 13 lean sedentary subjects (CTRL, age 27 ± 7 years; BMI 22 ± 3 kg/m2) participated in this study. Oxygen uptake (VO2), hearth rate (HR) and cardiac output (CO) were measured during cycle ergometer (CE) and knee extension (KE) incremental tests. Maximal voluntary contractions (MVCs) of knee extensor muscles were performed before and immediately after the two tests. RESULTS: VO2peak, HR peak and CO peak were significantly higher in CE than KE (+ 126%, + 33% and + 46%, respectively, p < 0.001), both in OB and CTRL subjects, without differences between the two subgroups. Maximal work rate was lower in OB than CTRL (191 ± 38 vs 226 ± 39 W, p < 0.05) in CE, while it was similar between the two subgroups in KE. Although CE and KE determined a reduction of MVC in both subgroups, MVC resulted less decreased after CE than KE exercises (- 14 vs - 32%, p < 0.001) in OB, while MVC decrements were similar after the two exercises in CTRL (- 26% vs - 30%, p > 0.05, for CE and KE, respectively). CONCLUSIONS: The lower muscle fatigue observed in OB after CE compared to KE test suggests that central factors could be the most important limiting factor during cycling in OB.

Short-Term Effects of Rolling Massage on Energy Cost of Running and Power of the Lower Limbs.

PURPOSE: Self-myofascial release (SMFR) is a type of self-massage that is becoming popular among athletes. However, SMFR's effects on running performance have not yet been investigated. The aim of this study was to evaluate the effects of SMFR on the cost of running (Cr). In addition, the authors evaluated the effects of SMFR on lower-limb muscle power. METHODS: Cr and lower-limb muscle power during squat jump (SJ) and countermovement jump (CMJ) were measured before (PRE), immediately after (POST), and 3 h after (POST 3h) an SMFR protocol (experimental condition). In the control-condition testing session, the same measurements were performed without undergoing the SMFR protocol. Experimental and control conditions were tested in a randomized order. RESULTS: Cr at POST trended to increase compared with PRE (+6.2% [8.3%], P = .052), whereas at POST 3h, Cr was restored to PRE values (+0.28% [9.5%], P = .950). In the experimental condition, no significant effect of time was observed for maximal power exerted during SJ. By contrast, maximal power exerted during CMJ at POST and at POST 3h was significantly higher than that observed at PRE (+7.9% [6.3%], P = .002 and +10.0% [8.7%], P = .004, respectively). The rate of force development measured during CMJ also increased after SMFR, reaching statistical significance at 200 ms from force onset at POST 3h (+38.9%, P = .024). CONCLUSIONS: An acute use of foam rollers for SMFR performed immediately prior to running may negatively affect endurance running performance, but its use should be added before explosive motor performances that include stretch-shortening cycles.

Effects of 14 days of bed rest and following physical training on metabolic cost, mechanical work, and efficiency during walking in older and young healthy males.

In this study, we investigated: i) the effects of bed rest and a subsequent physical training program on metabolic cost (Cw), mechanical work and efficiency during walking in older and young men; ii) the mechanisms underlying the higher Cw observed in older than young men.Twenty-three healthy male subjects (N = 16 older adults, age 59.6±3.4 years; N = 7 young, age: 23.1±2.9 years) participated in this study. The subjects underwent 14 days of bed rest followed by two weeks of physical training (6 sessions). Cw, mechanical work, efficiency, and co-contraction time of proximal muscles (vastus lateralis and biceps femoris) and distal muscles (gastrocnemius medialis and tibialis anterior) were measured during walking at 0.83, 1.11, 1.39, 1.67 m·s-1 before bed rest (pre-BR), after bed rest (post-BR) and after physical training (post-PT).No effects of bed rest and physical training were observed on the analysed parameters in either group. Older men showed higher Cw and lower efficiency at each speed (average +25.1 and -20.5%, P<0.001, respectively) compared to young. Co-contraction time of proximal and distal muscles were higher in older than in young men across the different walking speeds (average +30.0 and +110.3%, P<0.05, respectively).The lack of bed rest and physical training effects on the parameters analyzed in this study may be explained by the healthy status of both young and older men, which could have mitigated the effects of these interventions on walking motor function. On the other hand, the fact that older adults showed greater Cw, overall higher co-contraction time of antagonist lower limb muscles, and lower efficiency compared to the young cohort throughout a wide range of walking speed may suggest that older adults sacrificed economy of walking to improve stability.

Loss of maximal explosive power of lower limbs after 2 weeks of disuse and incomplete recovery after retraining in older adults.

KEY POINTS: Disuse in older adults can critically decrease lower limb muscle power, leading to compromised mobility and overall quality of life. We studied how muscle power and its determinants (muscle mass, single muscle fibre properties and motor control) adapted to 2 weeks of disuse and subsequent 2 weeks of physical training in young and older people. Disuse decreased lower limb muscle power in both groups; however, different adaptations in single muscle fibre properties and co-contraction of leg muscles were observed between young and older individuals. Six physical training sessions performed after disuse promoted the recovery of muscle mass and power. However, they were not sufficient to restore muscle power to pre-disuse values in older individuals, suggesting that further countermeasures are required to counteract the disuse-induced loss of muscle power in older adults. ABSTRACT: Disuse-induced loss of muscle power can be detrimental in older individuals, seriously impairing functional capacity. In this study, we examined the changes in maximal explosive power (MEP) of lower limbs induced by a 14-day disuse (bed-rest, BR) and a subsequent 14-day retraining, to assess whether the impact of disuse was greater in older than in young men, and to analyse the causes of such adaptations. Sixteen older adults (Old: 55-65 years) and seven Young (18-30 years) individuals participated in this study. In a subgroup of eight Old subjects, countermeasures based on cognitive training and protein supplementation were applied. MEP was measured with an explosive ergometer, muscle mass was determined by magnetic resonance, motor control was studied by EMG, and single muscle fibres were analysed in vastus lateralis biopsy samples. MEP was ∼33% lower in Old than in Young individuals, and remained significantly lower (-19%) when normalized by muscle volume. BR significantly affected MEP in Old (-15%) but not in Young. Retraining tended to increase MEP; however, this intervention was not sufficient to restore pre-BR values in Old. Ankle co-contraction increased after BR in Old only, and remained elevated after retraining (+30%). Significant atrophy occurred in slow fibres in Old, and in fast fibres in Young. After retraining, the recovery of muscle fibre thickness was partial. The proposed countermeasures were not sufficient to affect muscle mass and power. The greater impact of disuse and smaller retraining-induced recovery observed in Old highlight the importance of designing suitable rehabilitation protocols for older individuals.