Lower-extremity muscle activity during aquatic and land treadmill running at the same speeds.

CONTEXT: Muscle activation during aquatic treadmill (ATM) running has not been examined, despite similar investigations for other modes of aquatic locomotion and increased interest in ATM running. OBJECTIVES: The objectives of this study were to compare normalized (percentage of maximal voluntary contraction; %MVC), absolute duration (aDUR), and total (tACT) lower-extremity muscle activity during land treadmill (TM) and ATM running at the same speeds. DESIGN: Exploratory, quasi-experimental, crossover design. SETTING: Athletic training facility. PARTICIPANTS: 12 healthy recreational runners (age = 25.8 ± 5 y, height = 178.4 ± 8.2 cm, mass = 71.5 ± 11.5 kg, running experience = 8.2 ± 5.3 y) volunteered for participation. INTERVENTION: All participants performed TM and ATM running at 174.4, 201.2, and 228.0 m/min while surface electromyographic data were collected from the vastus medialis, rectus femoris, gastrocnemius, tibialis anterior, and biceps femoris. MAIN OUTCOME MEASURES: For each muscle, a 2 × 3 repeated-measures ANOVA was used to analyze the main effects and environment-speed interaction (P ≤ .05) of each dependent variable: %MVC, aDUR, and tACT. RESULTS: Compared with TM, ATM elicited significantly reduced %MVC (-44.0%) but increased aDUR (+213.1%) and tACT (+41.9%) in the vastus medialis, increased %MVC (+48.7%) and aDUR (+128.1%) in the rectus femoris during swing phase, reduced %MVC (-26.9%) and tACT (-40.1%) in the gastrocnemius, increased aDUR (+33.1%) and tACT (+35.7%) in the tibialis anterior, and increased aDUR (+41.3%) and tACT (+29.2%) in the biceps femoris. At faster running speeds, there were significant increases in tibialis anterior %MVC (+8.6-15.2%) and tACT (+12.7-17.0%) and rectus femoris %MVC (12.1-26.6%; swing phase). CONCLUSION: No significant environment-speed interaction effects suggested that observed muscle-activity differences between ATM and TM were due to environmental variation, ie, buoyancy (presumed to decrease %MVC) and drag forces (presumed to increase aDUR and tACT) in the water.

Comparison and reproducibility of sEMG during manual muscle testing on land and in water.

The objectives of this study were to: (1) compare the sEMG recordings from maximal voluntary contractions (MVC), and (2) examine the reproducibility of sEMG recordings from MVCs for selected lower extremity muscles derived from manual muscle testing (MMT) on dry land, and in water prior to and following aquatic treadmill running. Twelve healthy recreational male runners participated. The selected muscles were: M. quadriceps-vastus medialis (VM) and rectus femoris (RF), M. biceps femoris (BF), M. tibialis anterior (TA) and the M. gastrocnemius caput mediale (GAS) of the right leg. The MVC testing conditions were: dry land, underwater prior to (Water 1) and following an aquatic exercise trial (Water 2). For each muscle, a one-way analysis of variance with repeated measures was used to compare MVC scores between testing conditions, and the intra-class correlation coefficient (ICC) and typical error (CV%) were calculated to determine the reproducibility and precision of MVC scores, respectively, between conditions. For all muscles, no significant differences were observed between land and water MVC scores (p=0.88-0.97), and high reliability (ICC=0.96-0.98) and precision (CV%=7.4-12.6%) were observed between MVC conditions. Under MMT conditions it appears that comparable MVC sEMG values were achieved on land and in water and the integrity of the EMG recordings were maintained during water immersion. Future studies using sEMG waterproofing procedures should conduct MVC testing in water for data normalization and perform post-exercise verification of sEMG signal integrity.

Peak cardiorespiratory responses during aquatic and land treadmill exercise.

PURPOSE: Aquatic treadmill exercise has traditionally been used for aerobic training during rehabilitation; however, its ability to elicit comparable cardiorespiratory stress compared with land exercise is unclear. The purpose of this study was to investigate the cardiorespiratory (CR) responses elicited during maximal-effort protocols using an aquatic treadmill (ATM) and a land treadmill (TM). METHODS: Twenty-three college runners participated in two continuous, incremental peak oxygen consumption protocols (ATM and TM) until volitional exhaustion. For the ATM protocol, subjects were submerged in 28 degrees C water to the xiphoid process. ATM speed was increased incrementally to 206.8+/-23.1 m.min, and water jet resistance was increased 10% every minute thereafter. For the TM protocol, speed was increased to 205.3+/-22.3 m.min, and grade was increased 2% every minute thereafter. Rest between sessions was at least 48 h. Oxygen consumption (VO2), heart rate (HR), minute ventilation (VE), tidal volume (VT), breathing frequency (f), and respiratory exchange ratio (RER) were measured continuously, with peak values used for analysis. Rating of perceived exertion (RPE) was recorded immediately after each test, and blood lactate (LA) was measured 3 min afterward. RESULTS: VE and f were significantly greater in ATM versus TM; however, VO2, HR, VT, RER, LA, RPE, speed, and exercise times were similar for both protocols. CONCLUSIONS: Despite differences in VE and f, it seems that the fluid resistance created by water and jets in an ATM elicits peak CR responses comparable with those seen with inclined TM. These findings suggest that ATM running may be as effective as TM running for aerobic conditioning in fit individuals.