title: Lactate Threshold: Land versus Water Treadmill Running
Creators: name: Garner, Ron T.
Publisher: name: Utah State University
Year: 2013

description: Aquatic treadmill running has become increasingly popular for rehabilitation and training purposes due to decreased joint impact on the lower extremities, which is beneficial for special populations such as the injured, elderly, arthritic, and obese (Greene et al., 2009; Hall, Grant, Blake, Taylor, & Garbutt, 2004). Accordingly, researchers have compared key differences such as heart rate (HR), oxygen consumption (VO2), respiratory exchange ratio (RER), stride frequency, and rating of perceived exertion (RPE) between land and water running at maximal and submaximal efforts (Brubaker, Ozemek, Gonzalez, Wiley, & Collins, 2011; Rife, Myrer, Feland, Hunter, & Fellingham, 2010; Rutledge, Silvers, Browder, & Dolny, 2007; Silvers, Rutledge, & Dolny, 2007). As the benefits of aquatic treadmill running continue to be unveiled, there is an interest for healthy individuals to use the system to supplement training while limiting joint stress.
Rutledge et al. (2007) revealed VO2 values at 6.5, 7.5 and 8.5 mph on an aquatic treadmill with no jet resistance to be 33.97 ± 4.0, 37.96 ± 4.0, and 43.6 ± 4.0 mL•kg-1•min-1, respectively. Watson et al. (2012) also revealed VO2 values on an aquatic treadmill at 4.5, 6.0, and 7.5 mph with no jet resistance to be 20.58 ± 3.36, 29.27 ± 3.89, and 35.77 ± 4.02 mL•kg-1•min-1, respectively. These articles demonstrate the linear relationship that exists with increasing workloads with concomitant increases in VO2 with aquatic treadmill running. As metabolic demands increase, a reliance on anaerobic metabolism ensues and the work rate at which lactate begins to accumulate in the blood is called the lactate threshold (LT) (Stainsby & Brooks, 1990). The importance of determining LT is supported by a large body of evidence to predict aerobic endurance capacity (Faude, Kindermann, & Meyer, 2009). As such, researchers have employed great efforts to predict LT via field tests to determine the correct training intensity for endurance athletes (McGehee, Tanner, & Houmard, 2005).
An early study of LT revealed a strong relationship (r ≥ .91) between treadmill velocity at the onset of plasma lactate accumulation and running performance at distances ranging from 3.2 km to 42 km (Farrell, Wilmore, Coyle, Billing, and Costill, 1979). In other words, a faster sustainable work rate prior to a lactate accumulation or threshold will increase performance.
Comparisons for lactate concentrations during deep water and land treadmill running have been examined previously. Frangolias and Rhodes (1996) reviewed that during submaximal intensities of deep water versus land running, at the same relative VO2 water exercise resulted in a lower HR with higher blood lactate, RER, and RPE. These same authors previously reported that at maximal efforts on land versus deep water running, there was no statistical difference between lactate concentrations 30 s and 5 min post-exercise (Frangolias & Rhodes, 1995). However, not all water immersion running studies support similar peak lactate values (Frangolias & Rhodes, 1996; Svedenhag & Seger, 1992).
In a shallow water pool, a study by Town and Bradley (1991) revealed no statistical differences between land and water running for peak lactate values. However, lactate concentration in the water was 80% of that from land exercise. The authors stated that the “push-off” phase, which enabled ground contact, elicited similar running technique to land treadmills and could be partially responsible for similar physiological responses to land.
In recent years the availability of aquatic treadmills allows for a more favorable comparison of land and water running due to the implication of the “push-off” phase as discussed by Town and Bradley. Silvers et al. (2007) revealed no statistical difference between peak lactate concentrations in VO2peak tests run on land versus aquatic treadmills. Zobell (2009) examined a comparison of LT between land and aquatic treadmill running which showed higher lactate levels in the water compared to land. However, no clear answers have developed as to a comparison of the LT on land vs. aquatic treadmill running. Therefore, the purpose of this study was to determine the LT while running on a land and an aquatic treadmill and compare to see if the intensities are equivalent.