Strength exercises are usually characterized by high energy demand and restricted blood flow during time under tension (TUT). Thus, due to the hypoxic environment experienced by the exercising muscle, anaerobic energy metabolism plays an important role during resistance exercise. As a result, lactate production is increased in the working muscles, especially in type II muscle fibers, and consequently blood lactate concentration [La] increases. [La] depends on production, transportation, metabolism, and elimination of lactate and is commonly used to estimate lactate production/elimination in muscle (Beneke et al., 2011; Dotan, 2012). Although measurements of [La] were performed in investigations of hormonal responses to strength training (Kraemer and Ratamess, 2005; Lin et al., 2001; Vingren et al., 2008), neither transportation nor metabolism of lactate have been specifically investigated. However, [La] has been documented to assess metabolic demands resultant from different exercise protocols (Skidmore et al., 2012), i.e. various additional loads (Buitrago et al., 2012a; Kang et al., 2005; Thornton and Potteiger, 2002), movement velocities (Buitrago et al., 2012b; Gentil et al., 2006; Hunter et al., 2003), exercise volumes (1-set vs. multiple-sets) (Haddock and Wilkin, 2006), rest intervals (Ahtiainen et al., 2005; Denton and Cronin, 2006; Ratamess et al., 2007), and exercise order (Bellezza et al., 2009). Special conditions in the muscle lead to a specific metabolic situation during resistance exercises as intramuscular pressure exceed blood pressure and, as a consequence, blood flow is interrupted (Longhurst and Stebbins, 1997; Miles et al., 1987; Walloe and Wesche, 1988). As the muscle to blood lactate gradient, and therefore lactate transportation, is influenced by blood flow, it can be expected that different transportation rates occur during and between exercises in the course of an exercise protocol. We hypothesized that [La] would only slightly increase or stagnate during an exercise session and the increase in between the sets would decrease over the course of exercise.
Until now, no investigation has focused on how [La] develops in the course of resistance exercise with respect to different volume or exercise structure. However, such information would give an indication of the duration and level of metabolic stress experienced by the muscles and would provide information regarding the physiological processes of production, transportation, metabolism and elimination of lactate. Therefore, the aim of this study was to measure [La] over the course of multiple set resistance exercise protocols. Furthermore, we aimed to compare the time course of [La] accumulation in different muscle groups. We hypothesized that alterations in [La] would depend on muscle volume, and that [La] would not rise linearly, in the progression of a 3 set resistance exercise session, due to a suppressed ability of muscle to clear lactate during exercise.
Ten male healthy subjects (22.6 [+ or -] 2.0 years, height: 1.80 [+ or -] 0.05 m, weight: 73.5 [+ or -] 9.3 kg) with at least two years of strength training experience participated in the study. Participants were informed about the design and possible risks of the study and gave written informed consent to participate in this study. The investigations were done in accordance with the declaration of Helsinki and the Ethical Committee of the University.
Prior to the main experiments, subjects were familiarized with the experimental testing procedures and 10 repetition maximum (RM) was determined for Leg Extension (LE) and Arm Curl (AC) exercises (10 RM LE2: 103 [+ or -] 12kg; LE1: 51 [+ or -] 6kg; AC2: 66 [+ or -] 13kg; AC1: 33 [+ or -] 7kg). The 10 RM was determined as described by Baechle and Earle (2008). Velocity and range of motion (ROM) in all testing procedures were standardized by Biofeedback (Biofeedback 2.3.1, digimax): 2 seconds for concentric and eccentric phase each and 90[degrees] to 170[degrees] knee joints for LE exercise and from 170[degrees]-90[degrees] in elbow joints for the AC exercise. For the protocols where only one leg or one arm was exercised, half of the weight that was determined for both arms or legs was assigned. After determination of the 10 RM, it was tested again, to ensure that exhaustion occurred at the completion of 10 repetitions. Previous studies showed, that this kind of testing is a reliable method to determine additional load for training (Abernethy et al., 1995; Brown and Weir, 2001). Subjects performed four exercise protocols in a randomly chosen order: Leg Extension with one leg (LE1), Leg Extension with both legs (LE2), Arm Curl with one arm (AC1), Arm Curl with both arms (AC2). Each protocol consisted of 3 sets with the same muscle group with a 3 min rest period between each set. Before each protocol a warm up, consisting of 10 repetitions at 30% 10RM was performed. Sets were performed...