Low Body Fat Does Not Influence Recovery after Muscle-Damaging Lower-Limb Plyometrics in Young Male Team Sport Athletes

Aim: This study assessed the in uence of fat mass to fat-free mass ratio (FM:FFM) on recovery from plyometric exercise. Method: After assessment of body composition, 20 male team sport players (age 20.7 1.1 years; body mass 77.1 11.5 kg) were divided into low- (n=10; 0.11 0.03) and normal- (n=10; 0.27 0.09) fat groups based on FM:FFM ratio. Thereafter, participants completed measurements of knee extensor torque at 60 and 240 s 1 , countermovement jump ight time, plasma creatine kinase (CK) activity and perceived muscle soreness (VAS) before and at 0, 24 and 48 h after 10 10 maximal plyometric vertical jumps. Results: Evidence of muscle damage was con rmed by alterations in VAS, peak torque at 60 and 240 s 1 and ight time at 0, 24 and 48 h after plyometric exercise (P<0.05). CK was increased at 0 and 24 h (P<0.05) but returned to baseline values by 48 h. No time by group e ects were observed for any of the dependent variables (P>0.05). Conclusion: The current ndings indicate that while muscle damage was present after plyometric exercise, the magnitude was similar across the two body composition groups. Applied practitioners can allow for a similar recovery time after plyometric exercise in those with low and normal body fat. Keywords:exercise-induced muscle damage; stretch-shortening cycle; fat mass; muscle function 1. Introduction The stretch-shortening cycle underpins the mechanistic basis of plyometric exercise [1] that is widely used to advance athletic performance [2] and forms a natural part of many sporting movements. Indeed, plyometric training can provide a range of performance-related bene ts, including improvements in vertical jump height

normal body fat. Keywords:exercise-induced muscle damage; stretch-shortening cycle; fat mass; muscle function 1. Introduction The stretch-shortening cycle underpins the mechanistic basis of plyometric exercise [1] that is widely used to advance athletic performance [2] and forms a natural part of many sporting movements. Indeed, plyometric training can provide a range of performance-related bene ts, including improvements in vertical jump height [3], sprint performance [4], improved running economy [5] and skill-related actions [6]. A consequence of such training, however, particularly when it is unaccustomed or comprising high volume, is damage to the muscle ultra-structure [7]. The mechanisms of exercise-induced muscle damage (EIMD), which have been discussed extensively elsewhere [8,9], include mechanical (e.g., `popping' sarcomere hypothesis, impairments in excitation-contraction coupling) and metabolic (e.g., alterations in metabolic rate, glycogen depletion) disturbances. Notwithstanding its mechanisms, the symptoms of EIMD include increases in muscle soreness, intramuscular enzymes in the blood, and, of most importance to the athlete, an impaired muscle function that includes reductions in muscle strength and power [9,10]. These symptoms typically peak between 24 and 48 h after the initial bout and are recovered by seven days [9,10]. Although the acute indicators of EIMD are well-documented, little is known about the factors that exacerbate the associated symptoms and the subsequent recovery from this bout. Importantly, J. Funct. Morphol. Kinesiol.2020,5, 79; doi:10.3390 /jfmk5040079 /journal/jfmk

J. Funct. Morphol. Kinesiol.2020,5, 79 2 of 10 the appearance of these symptoms is not synchronous and often highly individualized [11,12]. One factor that might exacerbate symptoms of EIMD is the vertical loading on the muscle caused by the individual's body composition. Whilst lean tissue is functional and contributes to force-generating capacity, adipose tissue does not. Vertical loading is also known to be greater in obese compared to non-obese individuals [13]. It stands that body fat might act as a `vacant' load on the working muscles and has been shown to intensify symptoms after muscle-damaging exercise [14,15]. Hickner and colleagues reported that those with a higher fat-to-fat-free mass ratio (FM:FFM) experienced greater losses in muscular strength after downhill running [14]. Similarly, in the absence of any vertical loading (i.e., during knee extension exercise), Paschalis and colleagues [15] observed a greater magnitude of EIMD in overweight versus underweight females that might be in uenced by cytokine release and insulin resistance from greater adipose tissue [14]. Weak associations have also been reported between FM:FFM ratio and quadricep force loss after prolonged intermittent running in rugby players [16]. However, dissimilar patterns of vertical loading between downhill and intermittent shuttle running coupled with a homogenous group with similar body fat mass might explain these weak associations. Further work using damaging exercise with a greater vertical component (e.g., plyometric exercise) in a more heterogeneous group is therefore warranted. A study of this kind would have clear implications for those using damaging exercise with groups of individuals whose body composition varies. The purpose of this study was to assess the in uence of fat mass, using FM:FFM ratio, and the rate of recovery of indirect markers of exercise-induced muscle damage after plyometric exercise. 2. Materials and Methods 2.1. Participants Twenty recreational male team sport players (10 per group; age 20.7 1.1 years; body mass 77.1 11.5 kg; FM:FFM ratio 0.19 0.10) were recruited for the study. All participants were asymptomatic of illness and injury, and to negate the e ects of a prior bout of EIMD, participants had not performed systematic lower-limb training in the six

Methods 2.1. Participants Twenty recreational male team sport players (10 per group; age 20.7 1.1 years; body mass 77.1 11.5 kg; FM:FFM ratio 0.19 0.10) were recruited for the study. All participants were asymptomatic of illness and injury, and to negate the e ects of a prior bout of EIMD, participants had not performed systematic lower-limb training in the six months beforehand [17]. Participants provided written consent for the study, which was approved by the Ethics Committee of the host institution (SES121301; 26 June 2012). Participants were instructed not to consume any ergogenic supplements (for example, ca eine) on the day of testing and to refrain from exercise, other than that performed as part of the study, throughout their involvement. 2.2. Study Design The study used a repeated measures design in which participants attended the laboratory on four occasions (Figure). On the rst visit participants had their body composition assessed and were habituated to measures of muscle soreness, isokinetic knee extensor strength and maximal countermovement jump. Participants returned to the laboratory three days later for baseline measurements of plasma creatine kinase (CK) activity, muscle soreness, isokinetic extensor strength and maximal countermovement jump. Repeated measurements were conducted at 0, 24 1 and 48 1 h after muscle-damaging plyometric exercise (10 10 countermovement jumps). 2.3. Anthropometric Measurements The BodPod (S/T, Life Measurement Inc., Concord, CA, USA) was used as it is valid and non-invasive method to measure body composition [18], that demonstrates a low technical error and high internal validity [19]. This device employs air displacement plethysmography to measure body volume and subsequently body density. Thereafter, body fat percentage was estimated using the Siri equation from which body fat mass (FM; kg), fat-free mass (FFM; kg) and fat mass: fat free mass (FM:FFM; fat mass divided by fat-free mass) were calculated. Participants were divided into a

J. Funct. Morphol. Kinesiol.2020,5, 79 3 of 10 “low fat” (n=10) and “normal fat” group (n=10) for analysis based upon a median split of FM:FFM ratio. The terms and values “low fat” and “normal fat” are consistent with previous worked [14] and reference population data [20].J. Funct. Morphol. Kinesiol. 2020, 5, x FOR PEER REVIEW 3 of 11 Figure 1. Schematic of study design. 2.3. Anthropometric Measurements The BodPod (S/T, Life Measurement Inc., Concord, CA, USA) was used as it is valid and non- invasive method to measure body composition [18], that demonstrates a low technical error and high internal validity [19]. This device employs air displacement plethysmography to measure body volume and subsequently body density. Thereafter, body fat percentage was estimated using the Siri equation from which body fat mass (FM; kg), fat-free mass (FFM; kg) and fat mass: fat free mass (FM:FFM; fat mass divided by fat-free mass) were calculated. Participants were divided into a “low fat” (n = 10) and “normal fat” group (n = 10) for analysis based upon a median split of FM:FFM ratio. The terms and values “low fat” and “normal fat” are consistent with previous worked [14] and reference population data [20]. 2.4. Assessment of Perceived Muscle Soreness Perceived muscle soreness of the knee extensors was measured using a visual analogue scale (VAS). The VAS is numbered from 0 to 10 (on the concealed reverse side of the scale) where 0 indicates “no soreness on movement” and 10 indicates “muscles are too sore to move”. With feet shoulder width apart and hands on hips, participants descended until their hips were below their knee joint at which point the VAS was held up for them to indicate their rating of perceived soreness on the continuum. This method has been used previously as an indirect marker of muscle damage [21]. 2.5. Assessment of Plasma Creatine Kinase Activity Plasma CK activity was determined from a capillary blood sample of the participant’s preferred finger. A 30 µl sample of whole blood was collected into a heparinised capillary tube and pipetted onto a test strip for analysis (Reflotron,

continuum. This method has been used previously as an indirect marker of muscle damage [21]. 2.5. Assessment of Plasma Creatine Kinase Activity Plasma CK activity was determined from a capillary blood sample of the participant’s preferred finger. A 30 µl sample of whole blood was collected into a heparinised capillary tube and pipetted onto a test strip for analysis (Reflotron, Type 4, Boehringer Mannheim, Mannheim, Germany). The Reflotron employs a photometric process to determine CK activity. This procedure has been used previously to confirm tissue damage after exercise [21]. 2.6. Assessment of Knee Extensor Isokinetic Strength A dynamometer (Biodex, Multi-joint system 3, Biodex Medicial, New York, NY, USA) was used to measure isokinetic strength of the dominant knee extensors at velocities of 60°∙s −1 and 240°∙s −1 . To prevent extraneous body movements, Velcro straps were applied tightly across the chest and thigh. Participants were provided with strong verbal encouragement and real-time feedback via the computer’s monitor. Limb mass was calculated to enable gravitational correction and range of motion was set for each participant. Participants performed five repetitions at each speed, with the slower velocity employed first, to improve reliability, [22] and two minutes rest between sets [23]. The peak (i.e., highest value across the five repetitions) torque values were recorded and used for analysis. Familiarisation and anthropometry Markers of EIMD Plyometric exercise Markers of EIMD Markers of EIMD 72 hrs 24 hrs 24 hrs Markers of EIMD Figure 1.Schematic of study design. 2.4. Assessment of Perceived Muscle Soreness Perceived muscle soreness of the knee extensors was measured using a visual analogue scale (VAS). The VAS is numbered from 0 to 10 (on the concealed reverse side of the scale) where 0 indicates “no soreness on movement” and 10 indicates “muscles are too sore to move”. With feet shoulder width apart and hands on hips, participants descended until their hips were below their knee joint at which point the VAS was held up for them to indicate their rating of perceived soreness on the continuum. This method has been used previously as an indirect marker of muscle damage [21]. 2.5.

“muscles are too sore to move”. With feet shoulder width apart and hands on hips, participants descended until their hips were below their knee joint at which point the VAS was held up for them to indicate their rating of perceived soreness on the continuum. This method has been used previously as an indirect marker of muscle damage [21]. 2.5. Assessment of Plasma Creatine Kinase Activity Plasma CK activity was determined from a capillary blood sample of the participant's preferred nger. A 30 l sample of whole blood was collected into a heparinised capillary tube and pipetted onto a test strip for analysis (Re otron, Type 4, Boehringer Mannheim, Mannheim, Germany). The Re otron employs a photometric process to determine CK activity. This procedure has been used previously to con rm tissue damage after exercise [21]. 2.6. Assessment of Knee Extensor Isokinetic Strength A dynamometer (Biodex, Multi-joint system 3, Biodex Medicial, New York, NY, USA) was used to measure isokinetic strength of the dominant knee extensors at velocities of 60 s 1 and 240 s 1 . To prevent extraneous body movements, Velcro straps were applied tightly across the chest and thigh. Participants were provided with strong verbal encouragement and real-time feedback via the computer's monitor. Limb mass was calculated to enable gravitational correction and range of motion was set for each participant. Participants performed ve repetitions at each speed, with the slower velocity employed rst, to improve reliability, [22] and two minutes rest between sets [23]. The peak (i.e., highest value across the ve repetitions) torque values were recorded and used for analysis. 2.7. Assessment of Maximal Vertical Jump Height Maximal countermovement jump ight time was recorded using an infra-red timing system (Optojump, Microgate S.r.l., Bolzano, Italy). With their hands-on hips, participants squatted down into a self-selected depth before explosively performing the concentric action. Participants performed three maximal countermovement jumps with one-minute rest between each jump. This method has been used previously as an indirect marker of EIMD [24] and is a reliable marker of jump performance [25].

hands-on hips, participants squatted down into a self-selected depth before explosively performing the concentric action. Participants performed three maximal countermovement jumps with one-minute rest between each jump. This method has been used previously as an indirect marker of EIMD [24] and is a reliable marker of jump performance [25].

J. Funct. Morphol. Kinesiol.2020,5, 79 4 of 10 2.8. Muscle-Damaging Protocol The muscle-damaging exercises comprised 10 sets of 10 maximal countermovement jumps with 60 s rest between sets. Upon landing, participants were instructed to assume a 90 angle at the knee joint before the next jump. During the protocol, an infra-red timing system was used to record power output (Optojump, Microgate S.r.l., Bolzano, Italy). At the end of each set, participants were provided with feedback regarding their jump performance to encourage maximal e ort. The same method has successfully induced muscle damage in previous studies [23,26]. 2.9. Statistical Analysis All data collected were analyzed using SPSS (version 24, IBM SPSS Inc, Chicago, IL, USA). Assumptions of normal distribution and homogeneity of variance were checked via Shapiro Wilks and Levene statistics, respectively, and repeatedly found to be satis ed. An independent samplest-test was employed to compare anthropometric characteristics between groups. Thereafter, a two-way (time fat group) repeated measures analysis of variance tested the null hypothesis of no di erence between the two groups. Following a violation of Mauchly's test of Sphericity (P<0.05), the Greenhouse–Geisser correction was used. A post hoc t-test was conducted to locate the di erences between levels of the dependent variables, with a Tukey LSD correction [27]. Finally, e ects sizes (ES) (Cohen's d; di erence between the means divided by the pooled standard deviation) and 90% con dence intervals were calculated to determine the size of the di erences. The following quantitative criteria were used to explain the practical signi cance of the ndings: trivial<0.2, small 0.2–0.6, moderate>0.6–1.2, large> 1.2–2.0, and very large>2.0. Alpha was set at 0.05. 3. Results 3.1. Anthropometric Characteristics There were no di erences between groups for body mass (t= 0.1,P=0.951, ES=0.05 1.73). However, fat-free mass was greater in the low-fat group (t=2.6,P=0.020, ES= 1.13 0.94), whereas the normal-fat group had higher fat mass (t= 3.3,P=0.004, ES=4.50 3.14), body fat percentage (t= 5.6,P<0.001, ES=3.69 1.41) and FM:FFM ratio (t= 4.9,P<0.001, ES=4.24 1.91) than the low-fat group. All anthropometric data are shown in Table. Table 1. Anthropometric characteristics (mean standard deviation) and comparison of

However, fat-free mass was greater in the low-fat group (t=2.6,P=0.020, ES= 1.13 0.94), whereas the normal-fat group had higher fat mass (t= 3.3,P=0.004, ES=4.50 3.14), body fat percentage (t= 5.6,P<0.001, ES=3.69 1.41) and FM:FFM ratio (t= 4.9,P<0.001, ES=4.24 1.91) than the low-fat group. All anthropometric data are shown in Table. Table 1. Anthropometric characteristics (mean standard deviation) and comparison of low- and normal-fat groups. Characteristic Low Fat ( n=10) Normal Fat ( n=10) Body mass (kg) 76.9 6.1 77.2 15.5 Fat mass (kg) 8.0 1.8 16.7 8.2 * Fat-free mass (kg) 68.6 6.6 60.4 7.7 * Body fat (%) 10.6 2.5 20.8 5.1 * FM:FFM ratio 0.12 0.03 0.27 0.09 * * denotes signi cantly di erent between groups (P<0.05). 3.2. Muscle-Damaging Protocol There were no di erences in average ight time during the plyometric jumps between the low-fat (0.49 0.03 s) and normal-fat (0.46 0.06 s) groups (t=1.1,P=0.257, ES=0.73 1.32). 3.3. Plasma Creatine Kinase Activity A main e ect of time was revealed for CK activity after plyometric exercise (F=4.0,P=0.036), for which post hoc analysis revealed increases in plasma CK at 0 (t= 2.8,P=0.011 ES=0.12 0.63) and 24 h (t= 3.2,P=0.005, ES=0.58 0.77) after plyometric exercise (P<0.05). There was no group

J. Funct. Morphol. Kinesiol.2020,5, 79 5 of 10 (F=0.5,P=0.509) or time group interaction (F=0.7,P=0.743) for CK activity. Changes in CK activity are shown in Figure.J. Funct. Morphol. Kinesiol. 2020, 5, x FOR PEER REVIEW 5 of 11 3.2. Muscle-Damaging Protocol There were no differences in average flight time during the plyometric jumps between the low- fat (0.49 ± 0.03 s) and normal-fat (0.46 ± 0.06 s) groups (t = 1.1, P = 0.257, ES = 0.73 ± 1.32). 3.3. Plasma Creatine Kinase Activity A main effect of time was revealed for CK activity after plyometric exercise (F = 4.0, P = 0.036), for which post hoc analysis revealed increases in plasma CK at 0 (t = −2.8, P = 0.011 ES = 0.12 ± 0.63) and 24 h (t = −3.2, P = 0.005, ES = 0.58 ± 0.77) after plyometric exercise (P < 0.05). There was no group (F = 0.5, P = 0.509) or time x group interaction (F = 0.7, P = 0.743) for CK activity. Changes in CK activity are shown in Figure 2. Figure 2. Changes in creatine kinase (mean ± standard deviation) between low- and normal-fat groups at pre, 0, 24 and 48 h after resistance exercise. * denotes significantly different from pre for the whole sample (P < 0.05). 3.4. Perceived Muscle Soreness There was a main effect of time on perceived muscle soreness (F = 15.6, P < 0.001; Figure 3), with post hoc analysis revealing muscle soreness was higher at 0 h (t = −6.9, P < 0.001, ES = 2.13 ± 0.75), 24 h (t = −6.3, P < 0.001, ES = 2.31 ± 0.85) and 48 h (t = −4.4, P < 0.001, ES = 1.87 ± 0.83) after the muscle- damaging protocol (P < 0.05). There was no group (F = 0.1, P = 0.752) or time x group interaction for perceived muscle soreness (F = 1.1, P = 0.354). Figure 2. Changes in creatine kinase (mean standard deviation) between low- and normal-fat groups at pre, 0, 24 and 48 h after resistance exercise. * denotes signi cantly

the muscle- damaging protocol (P < 0.05). There was no group (F = 0.1, P = 0.752) or time x group interaction for perceived muscle soreness (F = 1.1, P = 0.354). Figure 2. Changes in creatine kinase (mean standard deviation) between low- and normal-fat groups at pre, 0, 24 and 48 h after resistance exercise. * denotes signi cantly di erent from pre for the whole sample (P<0.05). 3.4. Perceived Muscle Soreness There was a main e ect of time on perceived muscle soreness (F=15.6,P<0.001; Figure), with post hoc analysis revealing muscle soreness was higher at 0 h (t= 6.9,P<0.001, ES=2.13 0.75), 24 h (t= 6.3,P<0.001, ES=2.31 0.85) and 48 h (t= 4.4,P<0.001, ES=1.87 0.83) after the muscle-damaging protocol (P<0.05). There was no group (F=0.1,P=0.752) or time group interaction for perceived muscle soreness (F=1.1,P=0.354).J. Funct. Morphol. Kinesiol. 2020, 5, x FOR PEER REVIEW 6 of 11 Figure 3. Changes in perceived muscle soreness (mean ± standard deviation) between low- and normal-fat groups at pre, 0, 24 and 48 h after resistance exercise. * denotes significantly different from pre for the whole sample (P < 0.05). 3.5. Knee Extensor Isokinetic Strength A main effect of time on peak torque at 60 and 240°∙s −1 was observed (F = 7.6, P < 0.001 and F = 7.3, respectively, P < 0.001). After plyometric exercise peak torque for 60°∙s −1 was lower than baseline at 0 (t = 4.9, P < 0.001, ES = −0.41 ± 0.65), 24 (t = 5.5, P < 0.001, ES = −0.39 ± 0.63) and 48 h (t = 3.1, P = 0.006, ES = −0.18 ± 0.63). Similarly, peak torque at 240°∙s −1 was lower at 0 (t = 4.4, P < 0.001, ES = −0.38 ± 0.71), 24 (t = 3.6, P = 0.002, ES = −0.34 ± 0.59) and 48 h (t = 2.3, P = 0.033, ES = −0.09 ± 0.62) after plyometric exercise. However, there was no group (60°∙s −1 : F = 1.4, P = 0.255; 240°∙s −1 : F = 0.6, P = 0.469) or time x group interaction (60°∙s

The study investigates recovery differences in athletes based on body fat composition after plyometric exercises.