Effect of stride frequency on thermoregulatory responses during endurance running in distance runners

Changing stride frequency may influence oxygen uptake and heart rate during running as a function of running economy and central command. This study investigated the influence of stride frequency manipulation on thermoregulatory responses during endurance running. Seven healthy endurance runners ran on a treadmill at a velocity of 15 km/h for 60 min in a controlled environmental chamber (ambient temperature 27 °C and relative humidity 50%), and stride frequency was manipulated. Stride frequency was intermittently manipulated by increasing and decreasing frequency by 10% from the pre-determined preferred frequency. These periods of increase or decrease were separated by free frequency running in the order of free stride frequency, stride frequency manipulation (increase or decrease), free stride frequency, and stride frequency manipulation (increase or decrease) for 15 min each. The increased and decreased stride frequencies were 110% and 91% of the free running frequency, respectively (196±6, 162±5, and 178±5 steps/min, respectively, P<0.01). Compared to the control, stride frequency manipulation did not affect rectal temperature, heart rate, or the rate of perceived exhaustion during running. Whole-body sweat loss increased significantly when stride frequency was manipulated (1.48±0.11 and 1.57±0.11 kg for control and manipulated stride frequencies, respectively, P<0.05), but stride frequency had a small effect on sweat loss overall (Cohen's d=0.31). A higher mean skin temperature was also observed under mixed frequency conditions compared to that in the control (P<0.05). While the precise mechanisms underlying these changes remain unknown (e.g. running economy or central command), our results suggest that manipulation of stride frequency does not have a large effect on sweat loss or other physiological variables, but does increase mean skin temperature during endurance running.     

Effects of a concurrent strength and endurance training on running performance and running economy in recreational marathon runners

The purpose of this study was to investigate the effects of a concurrent strength and endurance training program on running performance and running economy of middle-aged runners during their marathon preparation. Twenty-two (8 women and 14 men) recreational runners (mean ± SD: age 40.0 ± 11.7 years; body mass index 22.6 ± 2.1 kg·m?2) were separated into 2 groups (n = 11; combined endurance running and strength training program [ES]: 9 men, 2 women and endurance running [E]: 7 men, and 4 women). Both completed an 8-week intervention period that consisted of either endurance training (E: 276 ± 108 minute running per week) or a combined endurance and strength training program (ES: 240 ± 121-minute running plus 2 strength training sessions per week [120 minutes]). Strength training was focused on trunk (strength endurance program) and leg muscles (high-intensity program). Before and after the intervention, subjects completed an incremental treadmill run and maximal isometric strength tests. The initial values for VO2peak (ES: 52.0 ± 6.1 vs. E: 51.1 ± 7.5 ml·kg?1·min?1) and anaerobic threshold (ES: 3.5 ± 0.4 vs. E: 3.4 ± 0.5 m·s?1) were identical in both groups. A significant time × intervention effect was found for maximal isometric force of knee extension (ES: from 4.6 ± 1.4 to 6.2 ± 1.0 N·kg?1, p < 0.01), whereas no changes in body mass occurred. No significant differences between the groups and no significant interaction (time × intervention) were found for VO2 (absolute and relative to VO2peak) at defined marathon running velocities (2.4 and 2.8 m·s?1) and submaximal blood lactate thresholds (2.0, 3.0, and 4.0 mmol·L?1). Stride length and stride frequency also remained unchanged. The results suggest no benefits of an 8-week concurrent strength training for running economy and coordination of recreational marathon runners despite a clear improvement in leg strength, maybe because of an insufficient sample size or a short intervention period.     

Effect of endurance training on oxygen uptake kinetics during treadmill running.

The purpose of this study was to examine the effect of endurance training on oxygen uptake (VO(2)) kinetics during moderate [below the lactate threshold (LT)] and heavy (above LT) treadmill running. Twenty-three healthy physical education students undertook 6 wk of endurance training that involved continuous and interval running training 3-5 days per week for 20-30 min per session. Before and after the training program, the subjects performed an incremental treadmill test to exhaustion for determination of the LT and the VO(2 max) and a series of 6-min square-wave transitions from rest to running speeds calculated to require 80% of the LT and 50% of the difference between LT and maximal VO(2). The training program caused small (3-4%) but significant increases in LT and maximal VO(2) (P<0.05). The VO(2) kinetics for moderate exercise were not significantly affected by training. For heavy exercise, the time constant and amplitude of the fast component were not significantly affected by training, but the amplitude of the VO(2) slow component was significantly reduced from 321+/-32 to 217+/-23 ml/min (P<0.05). The reduction in the slow component was not significantly correlated to the reduction in blood lactate concentration (r = 0. 39). Although the reduction in the slow component was significantly related to the reduction in minute ventilation (r = 0.46; P<0.05), it was calculated that only 9-14% of the slow component could be attributed to the change in minute ventilation. We conclude that the VO(2) slow component during treadmill running can be attenuated with a short-term program of endurance running training.     

Energy conservation attenuates the loss of skeletal muscle excitability during intense contractions

High-frequency stimulation of skeletal muscle has long been associated with ionic perturbations, resulting in the loss of membrane excitability, which may prevent action potential propagation and result in skeletal muscle fatigue. Associated with intense skeletal muscle contractions are large changes in muscle metabolites. However, the role of metabolites in the loss of muscle excitability is not clear. The metabolic state of isolated rat extensor digitorum longus muscles at 30 degrees C was manipulated by decreasing energy expenditure and thereby allowed investigation of the effects of energy conservation on skeletal muscle excitability. Muscle ATP utilization was reduced using a combination of the cross-bridge cycling blocker N-benzyl-p-toluene sulfonamide (BTS) and the SR Ca2+ release channel blocker Na-dantrolene, which reduce activity of the myosin ATPase and SR Ca2+-ATPase. Compared with control muscles, the resting metabolites ATP, phosphocreatine, creatine, and lactate, as well as the resting muscle excitability as measured by M-waves, were unaffected by treatment with BTS plus dantrolene. Following 20 or 30 s of continuous 60-Hz stimulation, BTS-plus-dantrolene-treated muscles showed a 25% lower ATP utilization compared with control muscles. Furthermore, the ability of muscles to maintain excitability during high-frequency stimulation was significantly improved in BTS-plus-dantrolene-treated muscles, indicating a strong link between metabolites, energetic state, and the excitability of the muscle.     

The effect of stride length on the dynamics of barefoot and shod running

A number of interventions and technique changes have been proposed to attempt to improve performance and reduce the number of running related injuries. Running shoes, barefoot running and alterations in spatio-temporal parameters (stride frequency and stride length) have been associated with significant kinematic and kinetic changes, which may have implications for performance and injury prevention. However, because footwear interventions have been shown to also affect spatio-temporal parameters, there is uncertainty regarding the origin of the kinematic and kinetic alterations. Therefore, the purpose of this study was to independently evaluate the effects of shoes and changes in stride length on lower extremity kinetics. Eleven individuals ran over-ground at stride lengths ±5 and 10% of their preferred stride length, in both the barefoot and shod condition. Three-dimensional motion capture and force plate data were captured synchronously and used to compute lower extremity joint moments. We found a significant main effect of stride length on anterior–posterior and vertical GRFs, and sagittal plane knee and ankle moments in both barefoot and shod running. When subjects ran at identical stride lengths in the barefoot and shod conditions we did not observe differences for any of the kinetic variables that were measured. These findings suggest that barefoot running triggers a decrease in stride length, which could lead to a decrease in GRFs and sagittal plane joint moments. When evaluating barefoot running as a potential option to reduce injury, it is important to consider the associated change in stride length.     

Potential for strength and endurance training to amplify endurance performance

The impact of adding heavy-resistance training to increase leg-muscle strength was studied in eight cycling- and running-trained subjects who were already at a steady-state level of performance. Strength training was performed 3 days/wk for 10 wk, whereas endurance training remained constant during this phase. After 10 wk, leg strength was increased by an average of 30%, but thigh girth and biopsied vastus lateralis muscle fiber areas (fast and slow twitch) and citrate synthase activities were unchanged. Maximal O2 uptake (VO2max) was also unchanged by heavy-resistance training during cycling (55 ml.kg-1.min-1) and treadmill running (60 ml.kg-1.min-1); however, short-term endurance (4-8 min) was increased by 11 and 13% (P less than 0.05) during cycling and running, respectively. Long-term cycling to exhaustion at 80% VO2max increased from 71 to 85 min (P less than 0.05) after the addition of strength training, whereas long-term running (10 km times) results were inconclusive. These data do not demonstrate any negative performance effects of adding heavy-resistance training to ongoing endurance-training regimens. They indicate that certain types of endurance performance, particularly those requiring fast-twitch fiber recruitment, can be improved by strength-training supplementation.     

Interaction between concurrent strength and endurance training

To assess the effects of concurrent strength (S) and endurance (E) training on S and E development, one group (4 young men and 4 young women) trained one leg for S and the other leg for S and E (S+E). A second group (4 men, 4 women) trained one leg for E and the other leg for E and S (E+S). E training consisted of five 3-min bouts on a cycle ergometer at a power output corresponding to that requiring 90-100% of oxygen uptake during maximal exercise (VO2 max). S training consisted of six sets of 15-20 repetitions with the heaviest possible weight on a leg press (combined hip and knee extension) weight machine. Training was done 3 days/wk for 22 wk. Needle biopsy samples from vastus lateralis were taken before and after training and were examined for histochemical, biochemical, and ultrastructural adaptations. The nominal S and E training programs were "hybrids", having more similarities as training stimuli than differences; thus S made increases (P less than 0.05) similar to those of S+E in E-related measures of VO2max (S, S+E: 8%, 8%), repetitions with the pretraining maximal single leg press lift [1 repetition maximum (RM)] (27%, 24%), and percent of slow-twitch fibers (15%, 8%); and S made significant, although smaller, increases in repetitions with 80% 1 RM (81%, 152%) and citrate synthase (CS) activity (22%, 51%). Similarly, E increased knee extensor area [computed tomography (CT) scans] as much as E+S (14%, 21%) and made significant, although smaller, increases in leg press 1 RM (20%, 34%) and thigh girth (3.4%, 4.8%). When a presumably stronger stimulus for an adaptation was added to a weaker one, some additive effects occurred (i.e., increases in 1 RM and thigh girth that were greater in E+S than E; increases in CS activity and repetitions with 80% 1 RM that were greater in S+E than S). When a weaker, although effective, stimulus was added to a stronger one, addition generally did not occur. Concurrent S and E training did not interfere with S or E development in comparison to S or E training alone.     

Metabolic, catecholamine, and endurance responses to caffeine during intense exercise

Jackman, M., P. Wendling, D. Friars, and T. E. Graham.Metabolic, catecholamine, and endurance responses to caffeine during intense exercise. J. Appl.Physiol. 81(4): 1658-1663, 1996.This studyexamined the possible effects of caffeine ingestion on muscle metabolism and endurance during brief intense exercise. We tested 14 subjects after they ingested placebo or caffeine (6 mg/kg) with anexercise protocol in which they cycled for 2 min, rested 6 min, cycled2 min, rested 6 min, and then cycled to voluntary exhaustion. In eachexercise the intensity required the subject's maximalO₂ consumption. Eight subjects hadmuscle and venous blood samples taken before and after each exerciseperiod. The caffeine ingestion resulted in a significant increase inendurance (4.12 ± 0.36 and 4.93 ± 0.60 min for placebo andcaffeine, respectively) and resulted in a significant increase inplasma epinephrine concentration throughout the protocol but not innorepinephrine concentration. During the first two exercise bouts, thepower and work output were not different; blood lactate concentrationswere not affected significantly by caffeine ingestion, but during theexercise bouts muscle lactate concentration was significantly increasedby caffeine. The net decrease in muscle glycogen was not differentbetween treatments at any point in the protocol, and even at the time of fatigue there was at least 50% of the original glycogenconcentration remaining. The data demonstrated that caffeine ingestioncan be an effective ergogenic aid for exercise that is as brief as4-6 min. However, the mechanism is not associated with muscleglycogen sparing. It is possible that caffeine is exerting actionsdirectly on the active muscle and/or the neural processes thatare involved in the activity.

     

Ten-day endurance training attenuates the hyperosmotic suppression of cutaneous vasodilation during exercise but not sweating.

It is well known that hyperosmolality suppresses thermoregulatory responses and that plasma osmolality (P(osmol)) increases with exercise intensity. We examined whether the decreased esophageal temperature thresholds for cutaneous vasodilation (TH(FVC)) and sweating (TH(SR)) after 10-day endurance training (ET) are caused by either attenuated increase in P(osmol) at a given exercise intensity or blunted sensitivity of hyperosmotic suppression. Nine young male volunteers exercised on a cycle ergometer at 60% peak oxygen consumption rate (V(O2 peak)) for 1 h/day for 10 days at 30 degrees C. Before and after ET, thermoregulatory responses were measured during 20-min exercise at pretraining 70% V(O2 peak) in the same environment as during ET under isoosmotic or hyperosmotic conditions. Hyperosmolality by approximately 10 mosmol/kgH2O was attained by acute hypertonic saline infusion. After ET, V(O2 peak) and blood volume (BV) both increased by approximately 4% (P < 0.05), followed by a decrease in TH(FVC) (P < 0.05) but not by that in TH(SR). Although there was no significant decrease in P(osmol) at the thresholds after ET, the sensitivity of increase in TH(FVC) at a given increase in P(osmol) [deltaTH(FVC)/deltaP(osmol), degrees C x (mosmol/kgH2O)(-1)], determined by hypertonic infusion, was reduced to 0.021 +/- 0.005 from 0.039 +/- 0.004 before ET (P < 0.05). The individual reductions in deltaTH(FVC)/deltaP(osmol) after ET were highly correlated with their increases in BV around TH(FVC) (r = -0.89, P < 0.005). In contrast, there was no alteration in the sensitivity of the hyperosmotic suppression of sweating after ET. Thus the downward shift of TH(FVC) after ET was partially explained by the blunted sensitivity to hyperosmolality, which occurred in proportion to the increase in BV.     

Calcaneus length determines running economy: implications for endurance running performance in modern humans and Neandertals

The endurance running (ER) hypothesis suggests that distance running played an important role in the evolution of the genus Homo. Most researchers have focused on ER performance in modern humans, or on reconstructing ER performance in Homo erectus, however, few studies have examined ER capabilities in other members of the genus Homo. Here, we examine skeletal correlates of ER performance in modern humans in order to evaluate the energetics of running in Neandertals and early Homo sapiens. Recent research suggests that running economy (the energy cost of running at a given speed) is strongly related to the length of the Achilles tendon moment arm. Shorter moment arms allow for greater storage and release of elastic strain energy, reducing energy costs. Here, we show that a skeletal correlate of Achilles tendon moment arm length, the length of the calcaneal tuber, does not correlate with walking economy, but correlates significantly with running economy and explains a high proportion of the variance (80%) in cost between individuals. Neandertals had relatively longer calcaneal tubers than modern humans, which would have increased their energy costs of running. Calcaneal tuber lengths in early H. sapiens do not significantly differ from those of extant modern humans, suggesting Neandertal ER economy was reduced relative to contemporaneous anatomically modern humans. Endurance running is generally thought to be beneficial for gaining access to meat in hot environments, where hominins could have used pursuit hunting to run prey taxa into hyperthermia. We hypothesize that ER performance may have been reduced in Neandertals because they lived in cold climates.     

Influence of exercise order on maximum strength and muscle volume in nonlinear periodized resistance training

The purpose of this study was to examine the influence of exercise order on strength and muscle volume (MV) after 12 weeks of nonlinear periodized resistance training. The participants were randomly assigned into 3 groups. One group began performing large muscle group exercises and progressed to small muscle group exercises (LG-SM), whereas another group started with small muscle group exercises and advanced to large muscle group exercises (SM-LG). The exercise order for LG-SM was bench press (BP), machine lat pull-down (LPD), triceps extension (TE), and biceps curl (BC). The order for the SM-LG was BC, TE, LPD, and BP. The third group did not exercise and served as a control group (CG). Training frequency was 2 sessions per week with at least 72 hours of rest between sessions. Muscle volume was assessed at baseline and after 6 weeks and 12 weeks of training by ultrasound techniques. One repetition maximum strength for all exercises was assessed at baseline and after 12 weeks of training. Effect size data demonstrated that differences in strength and MV were exhibited based on exercise order. Both training groups demonstrated greater strength improvements than the CG, but only BP strength increased to a greater magnitude in the LG-SM group as compared with the SM-LG. In all other strength measures (LPD, TE, and BC), the SM-LG group showed significantly greater strength increases. Triceps MV increased in the SM-LG group; however, biceps MV did not differ significantly between the training groups. In conclusion, if an exercise is important for the training goals of a program, then it should be placed at the beginning of the training session, regardless of whether or not it is a large muscle group exercise or a small muscle group exercise.     

Effects of Swiss-ball core strength training on strength, endurance, flexibility, and balance in sedentary women

The purpose of this study was to investigate the effects of Swiss-ball core strength training on trunk extensor (abdominal)/flexor (lower back) and lower limb extensor (quadriceps)/flexor (hamstring) muscular strength, abdominal, lower back and leg endurance, flexibility and dynamic balance in sedentary women (n = 21; age = 34 ± 8.09; height = 1.63 ± 6.91 cm; weight = 64 ± 8.69 kg) trained for 45 minutes, 3 d·wk-1 for 12 weeks. Results of multivariate analysis revealed significant difference (p ≤ 0.05) between pre and postmeasures of 60 and 90° s trunk flexion/extension, 60 and 240° s-1 lower limb flexion/extension (Biodex Isokinetic Dynamometer), abdominal endurance (curl-up test), lower back muscular endurance (modified Sorensen test), lower limb endurance (repetitive squat test), lower back flexibility (sit and reach test), and dynamic balance (functional reach test). The results support the fact that Swiss-ball core strength training exercises can be used to provide improvement in the aforementioned measures in sedentary women. In conclusion, this study provides practical implications for sedentary individuals, physiotherapists, strength and conditioning specialists who can benefit from core strength training with Swiss balls.     

Early phase changes by concurrent endurance and strength training

To compare regimens of concurrent strength and endurance training, 26 male basketball players were matched for stature, body composition, and physical activity level. Subjects completed different training programs for 7 weeks, 4 days per week. Groups were as follows: (a) the strength group (S; n = 7) did strength training; (b) the endurance group (E; n = 7) did endurance training; (c) the strength and endurance group (S + E; n = 7) combined strength and endurance training; and (d) the control group (C; n = 5) had no training. The S + E group showed greater gains in Vo(2)max than the E group did (12.9% vs. 6.8%), whereas the S group showed a decline (8.8%). Gains were noted in strength and vertical jump performance for the S + E and S groups. The S + E group had better posttraining anaerobic power than the S group did (6.2% vs. 2.9%). No strength, power, or anaerobic power gains were present for the E and C groups. We conclude that concurrent endurance and strength training is more effective in terms of improving athletic performance than are endurance and strength training apart.     

Glycogen utilization in rat respiratory muscles during intense running

Glycogen concentration in the adult rat diaphragm and intercostal muscles has been examined following heavy treadmill exercise to determine the recruitment strategy and the significance of glycogen as a substrate to satisfy the elevated energy requirements accompanying hyperpnea. Short-term continuous running at 60 m/min and a 12 degree grade resulted in a reduction (p less than 0.05) in the concentration of glycogen (39%) in the costal region of the rat diaphragm. Similarly, glycogen concentration was significantly reduced (p less than 0.05) with this exercise protocol in all respiratory muscles studied, with the exception of the sternal region of the diaphragm. With the less intense running protocols, glycogen degradation continued to be pronounced (p less than 0.05) in the majority of the respiratory muscles sampled. The significance of muscle glycogen as a substrate for energy metabolism in the respiratory muscles was not affected by the procedure used to prepare the animal for tissue sampling (Somnitol, diethyl ether, decapitation). Examination of selected locomotor muscles revealed extensive glycogen loss in muscles composed of essentially slow oxidative fibres (soleus), fast oxidative glycolytic fibres (vastus lateralis red), and fast glycolytic fibres (vastus lateralis white). It is concluded that during heavy exercise in the rat, recruitment of motor units occurs in all regions of the diaphragm and in the intercostal muscles. At least for the costal region of the diaphragm and as evidenced by the modest (two- to four-fold) but significant (p less than 0.05) increases in lactate concentration, the increased ATP requirements in these muscles are met to a large degree by increases in aerobic metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduced training intensities and loss of aerobic power, endurance, and cardiac growth

Twelve subjects participated in an exercise program of cycling and running 40 min/day, 6 days/wk. After 10 wk, they continued to train with either a one-third or two-thirds reduction in work rates for an additional 15 wk. Frequency and duration for the additional training remained the same as during the 10 wk of training. The average increases in maximum O2 uptake (VO2 max) were between 11 and 20% when measured during cycling and treadmill running after 10 wk of training. VO2 max was not maintained at the 6-day/wk training levels with a one-third reduction in training intensity but was still higher than pretraining levels. With a two-thirds reduction in intensity, VO2 max declined to an even greater extent than with the one-third reduction. Short-term endurance (approximately 5 min) was maintained in the one-third reduced group but was markedly reduced in the two-thirds reduced group. Long-term endurance was decreased significantly from training by 21% in the one-third reduced group (184-145 min) and by 30% in the two-thirds reduced group (202-141 min). Calculated left ventricular mass, obtained from echocardiographic measurements, increased approximately 15% after training but returned to control levels after reduced training in both groups. These results demonstrate that training intensity is an essential requirement for maintaining the increased aerobic power and cardiac enlargement with reduced training.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of linear vs. daily undulatory periodized resistance training on maximal and submaximal strength gains

The objective of this study was to verify the effect of 2 periodized resistance training (RT) methods on the evolution of 1-repetition maximum (1RM) and 8RM loads. Twenty resistance trained men were randomly assigned to 2 training groups: linear periodization (LP) group and daily undulating periodization (DUP) group. The subjects were tested at baseline and after 12 weeks for 1RM and 8RM loads in leg press (LEG) and bench press (BP) exercises. The training program was performed in alternated sessions for upper (session A: chest, shoulder and triceps) and lower body (session B: leg, back and biceps). The 12-week periodized training was applied only in the tested exercises, and in the other exercises, 3 sets of 6-8RM were performed. Both groups exhibited significant increases in 1RM loads on LEG and BP, but no statistically significant difference between groups was observed. The same occurred in 8RM loads on LEG and BP. However, DUP group presented superior effect size (ES) in 1RM and 8RM loads for LEG and BP exercises when compared to the LP group. In conclusion, periodized RT can be an efficient method for increasing the strength and muscular endurance in trained individuals. Although there was no statistically significant difference between periodization models, DUP promoted superior ES gains in muscular maximal and submaximal strength.     

Sex and stride length impact leg stiffness and ground reaction forces when running with body borne load

This study quantified leg stiffness and vGRF measures for males and females using different stride lengths to run with four body borne loads (20, 25, 30, and 35 kg). Thirty-six participants (20 males and 16 females) ran at 4.0 m/s using either: their preferred stride length (PSL), or strides 15% longer (LSL) and shorter (SSL) than PSL. Leg stiffness and vGRF measures, including peak vGRF, impact peak and loading rate, were submitted to a RM ANOVA to test the main effect and interactions of load, stride length, and sex. Leg stiffness was greater with the 30 kg (p = 0.016) and 35 kg (p < 0.001) compared to the 20 kg load, but decreased as stride lengthened from SSL to PSL (p < 0.001) and PSL to LSL (p < 0.001). Males exhibited greater leg stiffness than females with SSL (p = 0.029). Yet, males decreased leg stiffness with each increase in stride length (p < 0.001; p < 0.001), while females only decreased leg stiffness between PSL and LSL (p = 0.014). Peak vGRF was greater with the addition of body borne load (p < 0.001) and increase in stride length (p < 0.001). Both impact peak and loading rate were greater with the 30 kg (p = 0.034; p = 0.043) and 35 kg (p = 0.004; p = 0.015) compared to the 20 kg load, and increased as stride lengthened from SSL to PSL (p = 0.001; p = 0.004) and PSL to LSL (p < 0.001; p < 0.001). Running with body borne load may elevate injury risk by increasing leg stiffness and vGRFs. Injury risk may further increase when using longer strides to run with body borne load.