Glycemic control and hunger during recovery from high- and moderate-intensity Nordic skiing in well-trained skiers.

BACKGROUND: The aim of this paper was to study the effects of Nordic ski training on post-exercise blood glucose (BG) regulation. METHODS: Twenty-one (male N.=10; female N.=11) competitive college Nordic skiers (age 19.14±1.3 yrs; body fat percentage 14.9±6.2) completed two ski training conditions (high intensity [HI] and easy volume [MOD]) and one resting control (CON) condition on separate days. At rest on the control day and upon completion of ski training, a 75 g oral glucose tolerance test (OGTT) was administered. BG was measured prior to the OGTT and at 20-minute intervals for 80 minutes of passive rest. Hunger was assessed prior to the OGTT and at 40 and 80 minutes of rest via Visual Analog Scale. Data were analyzed using a two-way ANOVA with repeated measures and one-way ANOVA (SPSS v. 19). RESULTS: Significant time effects were present for BG. BG area under the curve (AUC) was significantly smaller (P<0.05) following HI (8825±149 arbitrary units [a.u.]) vs. CON (9493±168 a.u.), but not different from MOD (9087±227 a.u.). MOD AUC tended to be smaller than CON (P=0.064). Mean CON hunger was lower than MOD (P<0.05) and tended to be lower than HI (P=0.064). CONCLUSIONS: High-intensity Nordic skiing appears to enhance glycemic control when provided with an OGTT following acute exercise. The role that active muscle volume plays in this response should be investigated.

Influence of menstrual cycle on indices of contraction-induced muscle damage.

Limited evidence suggests women exhibit a dampened response to contraction-induced muscle damage (CIMD). The purpose of this study was to examine if differences in symptoms of CIMD exist when induced in the menstrual cycle follicular or luteal phase. Sixteen resistance exercise trained women between the ages of 18-37 completed 75 eccentric-biased extension exercises with their nondominant arm. Creatine kinase (CK), elbow joint angles, arm volume, strength, and soreness were measured over 7 days. Estrogen was higher (p < 0.001) in the luteal group. The high estrogen group (luteal) had an overall greater strength decrement and higher CK concentration at 96 hours. Significant time effects were present for CK, elbow extension, elbow flexion, arm volume, and soreness. With the exception of strength and CK, signs and symptoms of CIMD were independent of menstrual cycle phase. Estrogen concentration in women may have limited effects on symptoms associated with muscle damage, but further research in this area is warranted.

Prophylactic ankle taping: influence on treadmill-running kinematics and running economy.

Prophylactic ankle taping (PAT) is commonly used in sport. Prophylactic ankle taping may restrict ankle motion, which would affect the kinetic chain and alter gait. The purpose of this study was to examine the effects of PAT on lower extremity (LE) kinematics and running economy during treadmill running. Twelve recreational runners (9 women, 3 men; M ± SD age = 31.33 ± 8.04 years, height = 1.67 ± 0.81 m, mass = 61.84 ± 9.38 kg) completed two 20-minute running sessions (PAT and no tape: control [CON]) at a self-selected pace. Before each run, reflective markers were placed along the right side of the body. Sagittal plane kinematic data (60 Hz) were captured 4 times, and expired gases were measured for 2-minute after each video capture during both trials. Stride frequency, stride length, LE kinematic variables at initial contact and end contact (EC) were calculated. Cardiorespiratory variables and heart rate were also measured. Running economy was normalized to oxygen uptake per unit body mass per kilometer (milliliter per kilogram per kilometer) as running speeds varied. At EC, the PAT hip angle significantly decreased (p = 0.01) by 3.82°, whereas CON decreased by 0.85°. The range of motion tended to decrease over the 20-minute run (p = 0.08). Heart rate significantly increased over time (6.7%) but was not different between conditions. Prophylactic ankle taping did not significantly affect the physiological measures associated with the metabolic cost of treadmill running or the other kinematic variables. These findings suggest that the hip angle continued to decrease during the PAT condition at push-off in recreational runners without impacting the metabolic cost of transport.

The effects of a downhill running bout on running economy.

This study investigated whether downhill (DH) running (10-min @ 214.4 m·min(-1) and -10% grade) would elicit acute and delayed effects on running economy (RE) upon completion of DH running (RE2) and daily over 72 h (RE3, RE4, RE5). Fifteen runners (8 female, 7 male) completed the protocol. RE was measured during level running performed at 70% VO2peak. A baseline RE test (RE1) was used for comparison. Muscle soreness was significantly elevated at RE3 and RE4 vs. RE1. Oxygen uptake was significantly elevated at RE2 relative to RE3, RE4 and RE5 but was not different from RE1. Heart rate was similarly elevated at RE2. Measures of ankle, knee and hip joint angles at heel strike and toe off were not affected at any time-point in a subset of subjects (N = 6). A short DH running bout did not elicit significant delayed adverse effects on oxygen uptake or gait parameters relative to baseline.

Blood lactate concentration at the maximal lactate steady state is not dependent on endurance capacity in healthy recreationally trained individuals.

The aim of the study was to investigate the independent relationship between maximal lactate steady state (MLSS), blood lactate concentration [La] and exercise performance as reported frequently. Sixty-two subjects with a wide range of endurance performance (MLSS power output 199 ± 55 W; range: 100-302 W) were tested on an electronically braked cycle ergometer. One-min incremental exercise tests were conducted to determine maximal variables as well as the respiratory compensation point (RCP) and the second lactate turn point (LTP2). Several continuous exercise tests were performed to determine the MLSS. Subjects were divided into three clusters of exercise performance. Dietary control was employed throughout all testing. No significant correlation was found between MLSS [La] and power output at MLSS. Additionally, the three clusters of subjects with different endurance performance levels based on power output at MLSS showed no significant difference for MLSS [La]. MLSS [La] was not significantly different between men and women (average of 4.80 ± 1.50 vs. 5.22 ± 1.52 mmol l(-1)). MLSS [La] was significantly related to [La] at RCP, LTP2 and at maximal power. The results of this study support previous findings that MLSS [La] is independent of endurance performance. Additionally, MLSS [La] was not influenced by sex. Correlations found between MLSS [La] and [La] at maximal power and at designated anaerobic thresholds indicate only an association of [La] response during incremental and MLSS exercise when utilizing cycle ergometry.

The influence of parachute-resisted sprinting on running mechanics in collegiate track athletes.

The influence of parachute-resisted sprinting on running mechanics in collegiate track athletes. The aim of this investigation was to compare the acute effects of parachute-resisted (PR) sprinting on selected kinematic variables. Twelve collegiate sprinters (mean age 19.58 ± 1.44 years, mass 69.32 ± 14.38 kg, height 1.71 ± 9.86 m) ran a 40-yd dash under 2 conditions: PR sprint and sprint without a parachute (NC) that were recorded on a video computer system (60 Hz). Sagittal plane kinematics of the right side of the body was digitized to calculate joint angles at initial ground contact (IGC) and end ground contact (EGC), ground contact (GC) time, stride rate (SR), stride length (SL), and the times of the 40-yd dashes. The NC 40-yd dash time was significantly faster than the PR trial (p < 0.05). The shoulder angle at EGC significantly increased from 34.10 to 42.10° during the PR trial (p < 0.05). There were no significant differences in GC time, SR, SL, or the other joint angles between the 2 trials (p > 0.05). This study suggests that PR sprinting does not acutely affect GC time, SR, SL and upper extremity or lower extremity joint angles during weight acceptance (IGC) in collegiate sprinters. However, PR sprinting increased shoulder flexion by 23.5% at push-off and decreased speed by 4.4%. While sprinting with the parachute, the athlete's movement patterns resembled their mechanics during the unloaded condition. This indicates the external load caused by PR did not substantially overload the runner, and only caused a minor change in the shoulder during push-off. This sports-specific training apparatus may provide coaches with another method for training athletes in a sports-specific manner without causing acute changes to running mechanics.

Fluids and hydration in prolonged endurance performance.

Numerous studies have confirmed that performance can be impaired when athletes are dehydrated. Endurance athletes should drink beverages containing carbohydrate and electrolyte during and after training or competition. Carbohydrates (sugars) favor consumption and Na(+) favors retention of water. Drinking during competition is desirable compared with fluid ingestion after or before training or competition only. Athletes seldom replace fluids fully due to sweat loss. Proper hydration during training or competition will enhance performance, avoid ensuing thermal stress, maintain plasma volume, delay fatigue, and prevent injuries associated with dehydration and sweat loss. In contrast, hyperhydration or overdrinking before, during, and after endurance events may cause Na(+) depletion and may lead to hyponatremia. It is imperative that endurance athletes replace sweat loss via fluid intake containing about 4% to 8% of carbohydrate solution and electrolytes during training or competition. It is recommended that athletes drink about 500 mL of fluid solution 1 to 2 h before an event and continue to consume cool or cold drinks in regular intervals to replace fluid loss due to sweat. For intense prolonged exercise lasting longer than 1 h, athletes should consume between 30 and 60 g/h and drink between 600 and 1200 mL/h of a solution containing carbohydrate and Na(+) (0.5 to 0.7 g/L of fluid). Maintaining proper hydration before, during, and after training and competition will help reduce fluid loss, maintain performance, lower submaximal exercise heart rate, maintain plasma volume, and reduce heat stress, heat exhaustion, and possibly heat stroke.

Influence of carbohydrate delivery on the immune response during exercise and recovery from exercise.

Acute, sustained, moderate- to high-intensity exercise has been shown to induce significant alterations in the distribution and function of leukocytes during recovery. In many instances, these changes have been found to reflect a transient impairment of immune function in vitro during recovery from such exercise. Carbohydrate supplementation during exercise has been associated with an attenuation of cortisol production. Because cortisol has been linked to immunosuppression, a growing body of research has examined the influence of carbohydrate supplementation on immune function in response to exercise. New areas along this line of inquiry involve examination of the cytokine response to exercise and the role that carbohydrate may play in regulating the production of proinflammatory cytokines. Inter-relations among the immune response, production of specific cytokines, and cortisol are also examined. The clinical significance of an attenuated immune response when exercising as a result of the administration of supplemental carbohydrate is yet to be determined.

DOMS-associated changes in ankle and knee joint dynamics during running.

PURPOSE: The purpose of this study was to determine whether leg mechanics change due to DOMS by examining ankle and knee joint kinematics and stiffness before and after a down hill run. METHODS: Sagittal plane kinematics were recorded with high-speed (120 Hz) video at a speed representing 75% of VO2peak of nine well-trained male runners before (RE1) and 48 h after (RE2) a 30-min downhill run. From the recorded video, 10-12 consecutive strides were digitized, and the following variables were calculated for each stride: ankle and knee range of motion (ROM), ankle and knee peak angular velocity, ankle and knee stiffness, and leg vertical stiffness. A repeated measures ANOVA was calculated for each variable (alpha = 0.05). RESULTS: Both knee and ankle ROM during stance decreased with DOMS, but otherwise there were few changes in ankle mechanics with DOMS. Knee stiffness tended to increase during the early portion of stance (from initial stance to maximum angular velocity of flexion) with DOMS, immediately followed by a decrease (to maximum knee flexion) in stiffness. Changes in knee stiffness caused vertical leg stiffness to increase for the initial portion of stance with DOMS. CONCLUSION: Knee mechanics changed such that the knee stiffness increased at initial stance, resulting in an increase in vertical leg stiffness. This change in knee stiffness possibly serves as a protective mechanism to prevent further damage or pain in the knee extensor musculature.

The effects of a single bout of downhill running and ensuing delayed onset of muscle soreness on running economy performed 48 h later.

Delayed onset of muscle soreness (DOMS) is a common response to exercise involving significant eccentric loading. Symptoms of DOMS vary widely and may include reduced force generating capacity, significant alterations in biochemical indices of muscle and connective tissue health, alteration of neuromuscular function, and changes in mechanical performance. The purpose of the investigation was to examine the effects of downhill running and ensuing DOMS on running economy and stride mechanics. Nine, well-trained distance runners and triathletes participated in the study. Running economy was measured at three relative intensities [65, 75, and 85% of maximal aerobic capacity ( VO(2peak))] before (RE1) and 48 h after (RE2) a 30-min downhill run (-10%) at 70% VO(2peak). Dependent variables included leg muscle soreness, rate of oxygen consumption ( VO(2)), minute ventilation, respiratory exchange ratio, lactate, heart rate, and stride length. These measurements were entered into a two-factor multivariate analysis of variance (MANOVA). The analysis revealed a significant time effect for all variables and a significant interaction (time x intensity) for lactate. The energy cost of locomotion was elevated at RE2 by an average of 3.2%. This was coupled with a significant reduction in stride length. The change in VO(2) was inversely correlated with the change in stride length ( r= -0.535). Lactate was significantly elevated at RE2 for each run intensity, with a mean increase of 0.61 mmol l(-1). Based on these findings, it is suggested that muscle damage led to changes in stride mechanics and a greater reliance on anaerobic methods of energy production, contributing to the change in running economy during DOMS.