The effect of muscular endurance on running economy.
ABSTRACT The purpose of this study was to examine the relationship between fatigue-induced changes in running economy (RE) and muscular strength endurance (MSE). Ten well-trained male runners completed 2 runs of the same energy expenditure at 20%Δ VO(2) below LT. In the middle of the experimental condition (high intensity exercise [HIE]), there was a 4-minute block at sVO(2)max. The aim of the 4-minute block was to increase RE through fatigue, without inducing exhaustion. The MSE of hip extensors (HEs) and knee flexors (KFs) was assessed by 2 20-second eccentric bouts on an isokinetic dynamometer at 180°·s(-1). The RE increased after HIE compared to the control condition. Partial correlations found the increase in RE was strongly related with KF MSE (r = -0.709-0.798; p = 0.03-0.01). Greater MSE appeared to confer a fatigue resistant effect, resulting in a smaller increase in RE. The underlying mechanism of the fatigue resistant effect remains to be elucidated. Conditioning work focusing on augmenting eccentric muscular endurance of the legs may offer beneficial adaptations that promote fatigue resistance.
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ABSTRACT: Running economy (RE) represents a complex interplay of physiological and biomechanical factors that is typically defined as the energy demand for a given velocity of submaximal running and expressed as the submaximal oxygen uptake (VO2) at a given running velocity. This review considered a wide range of acute and chronic interventions that have been investigated with respect to improving economy by augmenting one or more components of the metabolic, cardiorespiratory, biomechanical or neuromuscular systems. Improvements in RE have traditionally been achieved through endurance training. Endurance training in runners leads to a wide range of physiological responses, and it is very likely that these characteristics of running training will influence RE. Training history and training volume have been suggested to be important factors in improving RE, while uphill and level-ground high-intensity interval training represent frequently prescribed forms of training that may elicit further enhancements in economy. More recently, research has demonstrated short-term resistance and plyometric training has resulted in enhanced RE. This improvement in RE has been hypothesized to be a result of enhanced neuromuscular characteristics. Altitude acclimatization results in both central and peripheral adaptations that improve oxygen delivery and utilization, mechanisms that potentially could improve RE. Other strategies, such as stretching should not be discounted as a training modality in order to prevent injuries; however, it appears that there is an optimal degree of flexibility and stiffness required to maximize RE. Several nutritional interventions have also received attention for their effects on reducing oxygen demand during exercise, most notably dietary nitrates and caffeine. It is clear that a range of training and passive interventions may improve RE, and researchers should concentrate their investigative efforts on more fully understanding the types and mechanisms that affect RE and the practicality and extent to which RE can be improved outside the laboratory.Sports Medicine 08/2014; DOI:10.1007/s40279-014-0246-y · 5.32 Impact Factor
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ABSTRACT: Abstract Vertical and leg stiffness are related to running speed. In endurance running, the ability to maintain stiffness might be more important than the absolute stiffness magnitude. The purpose of this study was to examine changes in vertical and leg stiffness during an exhaustive. Six sub-elite runners (24.2, s = 4.2 years; 1.81, s = 0.03 m; 73.4, s = 4.4 kg) participated in this study. They performed preliminary tests to determine lactate threshold, lactate turnpoint, [Formula: see text]O2max, s[Formula: see text]O2max and a series of isokinetic endurance tests. During the run to exhaustion runners were videoed (50 Hz) to determine contact and flight times, from which leg (Kleg) and vertical (Kvert) stiffness were calculated. During the run Kleg showed a significant decrease [P = 0.030, effect size statistics (ES) = 0.74], however, the decrease in Kvert was non-significant and of a small magnitude (P = 0.051, ES = 0.32). The distance covered during the run was correlated with ΔKleg (r = -0.868) but not ΔKvert (r = 0.684). ΔKleg was very strongly related to Δ ground contact time (r = -0.937) and Δ step length (r = -0.957). The Δ ground contact time had a near perfect relationship with Δ step length (r = 0.995). Isokinetic measures were not significantly correlated with either ΔKleg. The ability to maintain a short ground contact time appears to be a key determinant of maintaining performance during a run to exhaustion. Minimising this is important for maintaining Kleg. Kleg was not significantly related to isokinetic measures.01/2014; DOI:10.1080/17461391.2013.876102
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ABSTRACT: Sundby, ØH, Gorelick, M. Relationship between functional hamstring:quadriceps ratios and running economy in highly trained and recreational female runnersThe purpose of this study was to investigate the relationship between running economy (RE), functional hamstring:quadriceps peak torque ratios (f-H:Q) and flexibility among female runners. Seven highly trained female (HT) runners (age of 25.7 ± 4.7 yrs, VO2peak of 62.0 ± 4.8 mL·kg·min) and eleven recreational (REC) female runners (age of 28.8 ± 5.6 yrs, VO2peak of 49.2 ± 4.6 mL·kg·min) were measured for maximal aerobic power (VO2peak), RE, heart rate, respiratory exchange ratio (RER), f-H:Q (Hecc:Qcon and Hcon:Qecc), and sit-and-reach hamstring/trunk flexibility. On two separate days, RE was measured on a treadmill at 1% grade at two velocities (160.9 m·min and 201.2 m·min) for 6-min each, and isokinetic knee strength was measured at three angular velocities (60°·sec, 120°·sec, and 180°·sec) for both concentric and eccentric muscle actions. The unpaired t-tests showed a consistent trend towards higher f-H:Q ratios at all angular velocities among the HT runners. HT runners had significantly higher Hecc:Qcon at 120°·sec (p ≤ 0.05) and 180°·sec (p ≤ 0.05). Whole group correlations demonstrated a significant correlation between Hcon:Qecc at 180°·sec and RE (mL·kg·km) at 201.2 m·min (R = -0.48, p ≤ 0.05). No significant relationships were found between flexibility, or hamstring and quadriceps peak torque (N·m) and RE (p > 0.05). This cross-sectional analysis suggests that higher f-H:Q torque ratios, and not muscle strength per se, are associated with a lower metabolic cost of running. Therefore, runners should consider implementing hamstring exercises to improve their f-H:Q ratios.The Journal of Strength and Conditioning Research 01/2014; DOI:10.1519/JSC.0000000000000376 · 1.86 Impact Factor