Methods to identify the lactate and glucose thresholds during resistance exercise for individuals with type 2 diabetes

Intensity Thresholds and Maximal Lactate Steady State in Small Muscle Group Exercise

The aim of our study is to determine the first (LTP₁) and the second (LTP₂) lactate turn points during an incremental bicep curl test and to verify these turn points by ventilatory turn points (VT₁ and VT₂) and constant-load exercise tests. Twelve subjects performed a one-arm incremental bicep curl exercise (IET) after a one repetition maximum (1RM) test to calculate the step rate for the incremental exercise (1RM/45). Workload was increased every min at a rate of 30 reps/min until maximum. To verify LTPs, VT₁ and VT₂ were determined from spirometric data, and 30 min constant-load tests (CL) were performed at 5% P_max below and above turn points. Peak load in IET was 5.3 ± 0.9 kg (La_max: 2.20 ± 0.40 mmol·L⁻¹; HR_max: 135 ± 15 b·min⁻¹; VO_2max: 1.15 ± 0.30 L·min⁻¹). LTP₁ was detected at 1.9 ± 0.6 kg (La: 0.86 ± 0.36 mmol·L⁻¹; HR 90 ± 13 b·min⁻¹; VO₂: 0.50 ± 0.05 L·min⁻¹) and LTP₂ at 3.8 ± 0.7 kg (La: 1.38 ± 0.37 mmol·L⁻¹; 106 ± 10 b·min⁻¹; VO₂: 0.62 ± 0.11 L·min⁻¹). Constant-load tests showed a lactate steady-state in all tests except above LTP₂, with early termination after 16.5 ± 9.1 min. LTP₁ and LTP₂ could be determined in IET, which were not significantly different from VT₁/VT₂. Constant-load exercise validated the three-phase concept, and a steady-state was found at resting values below VT₁ and in all other tests except above LTP₂. It is suggested that the three-phase model is also applicable to small muscle group exercise.

Lactate and glucose thresholds and heart rate deflection points for Beagles during intense exercise

OBJECTIVE To determine whether the lactate threshold of dogs could be determined by a visual method and to assess the extent of agreement and bias among treadmill velocities for the lactate threshold as determined by visual (LTv) and polynomial (LTp) methods, glucose threshold as determined by visual (GTv) and polynomial (GTp) methods, and heart rate deflection point (HRdp) as a method for estimating the aerobic capacity of dogs. ANIMALS 18 healthy adult Beagles. PROCEDURES Each dog underwent a standardized incremental treadmill exercise test once. The test ended when the dog began to show signs of fatigue. Plasma lactate and glucose concentrations and heart rate (HR) were plotted against exercise intensity (treadmill velocity) for the duration of the test, and the LTv, GTv, and HRdp were determined visually. The LTp and GTp were determined by means of a second-order polynomial function. One-way ANOVA, Pearson correlation, Bland-Altman analyses, and ordinary least products regression were used to assess the extent of agreement and bias among the various threshold velocities. RESULTS Mean velocity did not differ significantly among the thresholds evaluated. There was a strong positive correlation between the LTv velocity and the velocity for GTv (r = 0.91), LTp (r = 0.96), GTp (r = 0.94), and HRdp (r = 0.95). CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that LTv could be determined for dogs undergoing intense exercise on a treadmill, and the treadmill velocity corresponding to the LTv was associated with the velocity for the other hallmarks of endurance. Thus, that method may be useful for prescription and evaluation of conditioning programs for dogs.

Psychophysiological characterization of different capoeira performances in experienced individuals: A randomized controlled trial

The aim of this study was to characterize the psychophysiological demand in different capoeira performances. Eleven experienced capoeira practitioners underwent the following procedures in different days: 1) anamnesis and anthropometric measurements; 2) aerobic performance assessment; 3 to 5) performances of 90 seconds in three capoeira styles (Angola, Benguela and São Bento), which were performed in randomized controlled cross-over design. The psychophysiological demand was assessed through the heart rate (HR), R-R interval (RRi), blood pressure (BP), blood lactate ([Lac]), blood glucose ([Gluc]), rating perceived effort (RPE), feeling scale (FS) and perceived activation (PA). Descriptive statistics with mean and standard deviation was performed. A two-way repeated measures ANOVA with Bonferroni post-hoc test was used. The Angola demand was between 56–71% maximal HR with [Lac]_PEAK: 6.9±2.9 mM, RPE_PEAK: 10.0±2.2 pts and FS: 2.7±1.7 pts, while in the Benguela participants reached 64–85% maximal HR with [Lac]_PEAK: 9.5±3.0 mM, RPE_PEAK: 11.0±2.8 pts and FS: 2.1±1.6 pts and for São Bento between 69–102% maximal HR with [Lac]_PEAK: 15.7±2.6 mM, RPE_PEAK: 15.5±4.1 pts and FS: -0.8±3.0 pts. Interaction time*performance occurred to [Lac] (F = 42.157; p<0.001), HR (F = 12.154; p<0.001), RRi (F = 4.774; p<0.001), parasympathetic modulation-rMSSD (F = 3.189; p<0.01), [Gluc] (F = 2.152; p<0.05), RPE (F = 5.855; p<0.01), FS (F = 2.448; p<0.05) and PA (F = 3.893; p<0.05). We concluded that São Bento rhythm resulted in a greater physiological demand according to the HR, [Lac] and cardiac autonomic indicators, with the Benguela rhythm being intermediate while the Angola rhythm presented a reduced demand. The [Gluc] increased after the São Bento rhythm when compared to the other rhythms. The perceptual demand presented increased in terms of RPE and PA variables and decreased in terms of FS when the São Bento performance was analyzed in comparison to the Angola and/or Benguela in capoeira.

Exercise timing and blood lactate concentrations in individuals with type 2 diabetes

The purpose of this study was to characterize how resistance exercise prior to or after a meal alters fasting and postprandial blood lactate concentrations in individuals with type 2 diabetes. Obese individuals with type 2 diabetes (N = 12) completed three 2-day trials, including (i) no exercise (NoEx), (ii) resistance exercise prior to dinner (Ex-M), and (iii) resistance exercise beginning at 45 min postdinner (M-Ex). During day 1 of each trial, fasting and postprandial blood lactate concentrations, perceived exertion, and substrate oxidation were measured, and subsequently on day 2 the following morning fasting blood lactate was measured. The premeal lactate incremental area under the curve (iAUC) during Ex-M (109 ± 66 mmol·L−1·1.6 h−1) was over 100-fold greater (P < 0.01) compared with NoEx (−15 ± 24 mmol·L−1·1.6 h−1) and M-Ex (−2 ± 18 mmol·L−1·1.6 h−1). The postprandial lactate iAUC during M-Ex (304 ± 116 mmol·L−1·4 h−1) was over 2-fold greater (P < 0.01) compared with NoEx (149 ± 74 mmol·L−1·4 h−1) and Ex-M (−140 ± 196 mmol·L−1·4 h−1). Average lactate during exercise was ∼45% greater (P = 0.03) during M-Ex (3.2 ± 0.9 mmol/L) compared with Ex-M (2.2 ± 0.9 mmol/L), but the change in lactate during Ex-M (2.4 ± 1.6 mmol/L) or M-Ex (2.3 ± 1.3 mmol/L) was not different (P > 0.05). Perceived exertion, substrate oxidation, or fasting blood lactate concentrations the day after testing were not different between trials. Blood lactate concentrations during acute resistance exercise are greater when exercise is performed in the postprandial period. Acute resistance exercise performed the night prior does not alter fasting blood lactate concentrations the following morning.

Is heart rate variability a feasible method to determine anaerobic threshold in progressive resistance exercise in coronary artery disease?

Background

Recent studies have shown that the magnitude of the metabolic and autonomic responses during progressive resistance exercise (PRE) is associated with the determination of the anaerobic threshold (AT). AT is an important parameter to determine intensity in dynamic exercise.

Objectives

To investigate the metabolic and cardiac autonomic responses during dynamic resistance exercise in patients with Coronary Artery Disease (CAD).

Method

Twenty men (age = 63±7 years) with CAD [Left Ventricular Ejection Fraction (LVEF) = 60±10%] underwent a PRE protocol on a leg press until maximal exertion. The protocol began at 10% of One Repetition Maximum Test (1-RM), with subsequent increases of 10% until maximal exhaustion. Heart Rate Variability (HRV) indices from Poincaré plots (SD1, SD2, SD1/SD2) and time domain (rMSSD and RMSM), and blood lactate were determined at rest and during PRE.

Results

Significant alterations in HRV and blood lactate were observed starting at 30% of 1-RM (p<0.05). Bland-Altman plots revealed a consistent agreement between blood lactate threshold (LT) and rMSSD threshold (rMSSDT) and between LT and SD1 threshold (SD1T). Relative values of 1-RM in all LT, rMSSDT and SD1T did not differ (29%±5 vs 28%±5 vs 29%±5 Kg, respectively).

Conclusion

HRV during PRE could be a feasible noninvasive method of determining AT in CAD patients to plan intensities during cardiac rehabilitation.

LIMIAR ANAERÓBIO A PARTIR DA PSE EM EXERCÍCIO RESISTIDO POR MODELOS MATEMÁTICOS

Introdução: O limiar anaeróbio é comumente identificado em exercícios cíclicos, contudo, também pode ser determinado no exercício resistido (ER) por diferentes métodos, e assim, estimar a carga de trabalho relacionada ao estresse metabólico. No entanto, sua identificação a partir de outros métodos como o modelo matemático da DMáx e principalmente por variáveis mais acessíveis, como a percepção subjetiva de esforço (PSE), ainda não foi analisada. Objetivo: Comparar o limiar de lactato (LL) identificado pelo método de inspeção visual (LLIV) com o método da DMáx aplicado nas respostas do lactato (LLDMáx) e da PSE (PSE12/13 e PSEDMáx) durante exercício resistido incremental. Métodos: Dez praticantes de ER (24,8 ± 3,0 anos) foram submetidos ao teste de uma repetição máxima (1-RM) e a um teste incremental no leg-press, obtendo-se a PSE e o lactato em cada estágio. Resultados: Foi possível identificar o limiar anaeróbio por todos os métodos, entre 30% a 40% de 1-RM. As cargas absolutas, concentrações de lactato sanguíneo e PSE não foram diferentes entre os métodos empregados e apresentaram boa concordância entre si. Conclusão: É possível identificar o limiar anaeróbio tanto por inspeção visual quanto pelo modelo matemático de DMáx para o lactato e PSE, ampliando as possibilidades de determinação do limiar anaeróbio no exercício resistido por métodos de baixo custo e não invasivos.

Combined exercise circuit session acutely attenuates stress-induced blood pressure reactivity in healthy adults

Objective

To investigate the blood pressure (BP) responses to cardiovascular stress test after a combined exercise circuit session at moderate intensity.

Method

Twenty individuals (10 male/10 fem; 33.4± 6.9 years; 70.2± 15.8 kg; 170.4± 11.5 cm; 22.3± 6.8% body fat) were randomized in a different days to control session with no exercise or exercise session consisting of 3 laps of the following circuit: knee extension, bench press, knee flexion, rowing in the prone position, squats, shoulder press, and 5 min of aerobic exercise at 75-85% of age-predicted maximum heart rate and/or 13 on the Borg Rating of Perceived Exertion [scale of 6 to 20]. The sets of resistance exercise consisted of 15 repetitions at ~50% of the estimated 1 repetition maximum test. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured at rest and during 1h of recovery in both experimental sessions. After that, blood pressure reactivity (BP_R) was evaluated using the Cold Pressor Test.

Results

During 1h of exercise recovery, there was a reduction in SBP (3-6 mmHg) and DBP (2-5 mmHg) in relation to pre-session rest (p<0.01), while this reduction was not observed in the control session. A decline in BP_R (4-7 mmHg; p<0.01) was observed 1h post-exercise session, but not in the control session. Post-exercise reductions in SBP and DBP were significantly correlated with BP_R reductions (r=0.50-0.45; p<0.05).

Conclusion

A combined exercise circuit session at moderate intensity promoted subsequent post-exercise hypotension and acutely attenuated BP_R in response to a cardiovascular stress test. In addition, the post-exercise BP reduction was correlated with BP_R attenuation in healthy adults of both genders.

Identification of anaerobic threshold by analysis of heart rate variability during discontinuous dynamic and resistance exercise protocols in healthy older men

The purposes of this study were to determine anaerobic threshold (AT) during discontinuous dynamic and resistive exercise protocols by analysing of heart rate variability (HRV) and blood lactate (BL) in healthy elderly subjects and compare the cardiovascular, metabolic and autonomic variables obtained from these two forms of exercise. Fourteen elderly (70 ± 4 years) apparently healthy males underwent the following tests: (i) incremental ramp test on cycle ergometer, (ii) one repetition maximum (1RM) leg press at 45°, (iii) a discontinuous exercise test on a cycle ergometer (DET-C) protocol and (iv) a resistance exercise leg press (DET-L) protocol. Heart rate, blood pressure and BL were obtained during each increment of exercise intensity. No significant differences (P>0·05) were found between methods of AT determination (BL and HRV) nor the relative intensity corresponding to AT (30% of maximum intensity) between the types of exercise (DET-C and DET-L). Furthermore, no significant differences (P>0·05) were found between the DET-C and DET-L in relation to HRV, however, the DET-L provided higher values of systolic blood pressure and BL (P<0·05) from the intensity corresponding to AT. We conclude that HRV was effective in determination of AT, and the parasympathetic modulation responses obtained during dynamic and resistive exercise protocols were similar when compared at the same relative intensity. However, DET-L resulted in higher values of blood pressure and BL at workloads beyond AT.

Efeitos do calor no OBLA: comparação entre ambiente quente e temperado

O OBLA (onset of blood lactate accumulation) é um método utilizado para estimar o limiar de lactato (LL). Entretanto, ainda não está claro o efeito da temperatura ambiente sobre o OBLA. O objetivo do presente estudo foi comparar o OBLA em ambiente quente (40ºC) e temperado (22ºC). Nove homens (idade: 23,9±2,4 anos; massa corporal: 75,9±7,3 kg e VO2máx: 47,8±4,9 mL•kg-1•min-1) realizaram teste progressivo em cicloergômetro para determinação da potência máxima (Wmáx) e do OBLA nos dois ambientes. A Wmáx (195±25W vs 225±28W) e a potência no OBLA (153±30W vs 165±32W) foram menores no ambiente quente do que no temperado. A frequência cardíaca no OBLA-40 foi maior do que no OBLA-22 (171±8 vs 153±10 bpm, respectivamente). Não foi observada diferença no consumo de oxigênio no OBLA-22 e OBLA-40 (31,65±5,21 vs 31,12±6,82 mL•kg-1•min-1). Estes resultados indicam que as condições ambientais influenciam a determinação do OBLA.

Blood glucose control for individuals with type-2 diabetes: acute effects of resistance exercise of lower cardiovascular-metabolic stress

This study compared the effects of resistance exercise (RE) intensities on blood glucose (GLUC) of individuals without (ND) and with type-2 diabetes (T2D). Nine individuals with T2D and 10 ND performed: (a) RE circuit at 23% of 1 maximal repetition (1RM) (RE_L); (b) RE circuit at 43% 1RM (RE_M); and (c) control (CON) session. Blood lactate (LAC) and GLUC were measured before, during, and postinterventions. Double product (DP) and rate of perceived exertion (RPE) were recorded. The area under the curve (AUC) revealed the effects of RE circuits in reducing GLUC in individuals with T2D (RE_L: 12,556 ± 3,269 vs. RE_M: 13,433 ± 3,054 vs. CON: 14,576 ± 3,922 mg.dl(-1).145 minutes; p < 0.05) with a lower AUC of GLUC in RE_L in comparison to RE_M. Similarly, for ND the RE_L reduced the AUC of GLUC when compared with RE_M and CON (RE_L: 10,943 ± 956 vs. RE_M: 12,156 ± 1,062 vs. CON: 11,498 ± 882 mg.dl(-1).145 minutes; p < 0.05). The AUC of GLUC was higher for T2D compared with ND on CON condition (p = 0.02). However, after RE circuits the difference between groups for AUC of GLUC was abolished. The RE_M for T2D was more stressful when compared with RE_L for LAC (CON: 1.3 ± 0.5 vs. RE_L: 5.5 ± 1.5 vs. RE_M: 6.8 ± 1.3 mmol·L(-1); p < 0.05), DP (CON: 8,415 ± 1,223 vs. RE_L: 15,980 ± 2,007 vs. RE_M: 18,047 ± 3,693 mmHg.bpm(-1); p < 0.05), and RPE (RE_L: 11 ± 2 vs. RE_M: 13 ± 2 Borg Scale; p < 0.05). We concluded that RE_L and RE_M were effective in reducing GLUC for individuals with T2D, with lower cardiovascular-metabolic and perceptual stress being observed for RE_L. These data suggest that acute RE sessions at light or moderate intensities are effective for controlling GLUC in individuals with T2D.

Reprodutibilidade do protocolo de lactato mínimo com intensidade do esforço prévio individualizado pela PSE

Introdução: O protocolo de lactato mínimo (LM) é precedido de um esforço máximo para indução a hiperlactatemia. Objetivo: Verificar a reprodutibilidade de um teste de LM com indução à hiperlactatemia realizada em teste incremental com cargas individualizadas através da percepção subjetiva de esforço (PSE). Metodologia: A amostra foi composta por 20 estudantes fisicamente ativos (25,4 ± 4,1 anos; 14,1 ± 5,0 % gordura), submetidos a dois testes de LM com metodologia idêntica. A indução a hiperlactatemia foi realizada por um teste com quatro estágios, com duração de três minutos cada e cargas individualizadas pela PSE (níveis 10, 13, 16 e o último estágio 17-20 até a exaustão voluntária). Após oito minutos de recuperação o teste progressivo começou com carga inicial de 75 W e incrementos de 25 W a cada três minutos, até a exaustão. Resultados: As intensidades de LM 1 (155,0 ± 23,8 W) e LM 2 (157,5 ± 27,0 W) não diferiram estatisticamente (p = 0,795) e de uma maneira geral apresentaram boa reprodutibilidade (CCI = 0,79) e concordância [-2,5 W de média da diferença e ± 41,8 W de abas]. Conclusão: O teste de LM, com cargas para hiperlactatemia individualizadas pela PSE, se mostrou reprodutível em indivíduos fisicamente ativos.

Different cardiovascular responses to a resistance training session in hypertensive women receiving propanolol compared with normotensive controls

The aim of the present study was to compare the responses of blood pressure, heart rate, and rate-pressure product of hypertensive women using beta-blockers with healthy controls during resistance exercise (by the end of the concentric phase of the contractions) and in the postexercise period (5 and 30 minutes after). Ten untrained normotensive women (N) and 10 mildly hypertensive females receiving 40 mg/day of propanolol (H) were selected. Three sets of 10 repetitions at 80% of 10 repetitions maximum with 30 s rest interval were performed on the leg press exercise. The H group exhibited lower systolic blood pressure after the second set compared with N. Heart rate and rate-pressure product were lower in H in all analyzed periods compared with N. Propanolol attenuates the cardiovascular response to a leg press resistance exercise in mildly hypertensive women.

Noninvasive method to estimate anaerobic threshold in individuals with type 2 diabetes

BACKGROUND

While several studies have identified the anaerobic threshold (AT) through the responses of blood lactate, ventilation and blood glucose others have suggested the response of the heart rate variability (HRV) as a method to identify the AT in young healthy individuals. However, the validity of HRV in estimating the lactate threshold (LT) and ventilatory threshold (VT) for individuals with type 2 diabetes (T2D) has not been investigated yet.

AIM

To analyze the possibility of identifying the heart rate variability threshold (HRVT) by considering the responses of parasympathetic indicators during incremental exercise test in type 2 diabetics subjects (T2D) and non diabetics individuals (ND).

METHODS

Nine T2D (55.6 ± 5.7 years, 83.4 ± 26.6 kg, 30.9 ± 5.2 kg.m2(-1)) and ten ND (50.8 ± 5.1 years, 76.2 ± 14.3 kg, 26.5 ± 3.8 kg.m2(-1)) underwent to an incremental exercise test (IT) on a cycle ergometer. Heart rate (HR), rate of perceived exertion (RPE), blood lactate and expired gas concentrations were measured at the end of each stage. HRVT was identified through the responses of root mean square successive difference between adjacent R-R intervals (RMSSD) and standard deviation of instantaneous beat-to-beat R-R interval variability (SD1) by considering the last 60 s of each incremental stage, and were known as HRVT by RMSSD and SD1 (HRVT-RMSSD and HRVT-SD1), respectively.

RESULTS

No differences were observed within groups for the exercise intensities corresponding to LT, VT, HRVT-RMSSD and HHVT-SD1. Furthermore, a strong relationship were verified among the studied parameters both for T2D (r = 0.68 to 0.87) and ND (r = 0.91 to 0.98) and the Bland & Altman technique confirmed the agreement among them.

CONCLUSION

The HRVT identification by the proposed autonomic indicators (SD1 and RMSSD) were demonstrated to be valid to estimate the LT and VT for both T2D and ND.

Heart-rate variability and blood-lactate threshold interaction during progressive resistance exercise in healthy older men

The objective of this study was to (a) evaluate the impact of the leg press, at variable percentages of 1 repetition maximum (1RM), on heart rate variability (HRV) and blood lactate and (b) determine the relationship between HRV with blood lactate in a healthy elderly cohort. Ten healthy men (64 +/- 4 years) participated in a progressive leg-press protocol to maximal exertion. Initially, 1RM for the leg press was determined for all subjects. The protocol then began at 10% of 1RM, with subsequent increases of 10% until 30% of 1RM, followed by incremental adjustments of 5% until exhaustion. The measurement of instantaneous R-R interval variability from Poincare plots (SD1 and SD2) and time domain indexes (RMSSD and RMSM), blood pressure, and blood lactate were obtained at rest and all leg-press loads. Significant alterations of HRV and blood lactate were observed from 30% of 1RM leg press (p < 0.05). Additionally, significant correlations were found between the lactate threshold (LT) and the RMSSD threshold (r = 0.78; p < 0.01), and between the LT and SD1 threshold (r = 0.81, p < 0.01). We conclude that metabolic and cardiovascular alterations are apparent during relatively low resistance exercise (RE) loads in apparently healthy subjects. In addition, HRV indexes were associated with blood-lactate levels during RE. The practical applications is the possibility of using HRV as a noninvasive measure obtained at a relatively low cost may be used to identify neural and metabolic alterations during RE in older subjects.

A Variação do método de incremento de cargas não altera a determinação do limiar de lactato em exercício resistido

Com o objetivo de analisar e comparar diferentes protocolos incrementais (PI) em exercício resistido para a identificação do limiar de lactato (LL), 12 voluntários homens (23,3 ± 1,6 anos) adaptados ao exercício resistido foram submetidos a dois testes incrementais realizados em leg press 45º (LP). Os PI's foram: 1) relativo ao teste da carga máxima (PI%1RM), com incrementos de 19, 28, 32, 37, 41, 45, 55 e 60% de 1RM; 2) relativo ao peso corporal (PI%PC), com incrementos de 17, 33, 50, 67, 83, 100, 117 e 133% do PC. Em ambos os PI's a duração de cada estágio foi de 1 min, sendo realizadas 30 repetições em cada. Durante os intervalos entre cada estágio (2 min para o PI%1RM e de 1 min para o PI%PC) foram coletados do lóbulo da orelha, 25µL de sangue capilarizado, os quais foram depositados em microtúbulos Eppendorff para posterior dosagem das concentrações de lactato sanguíneo [Lac]. Foi possível identificar o LL a partir da resposta das [Lac] nos diferentes protocolos. Não foram observadas diferenças significativas entre o LL determinado por cargas absolutas (PI%1RM - 72,3 ± 12,5 vs. PI%PC - 65,9 ± 11,5kg; p > 0,05) e relativas (PI%1RM - 32,3 ± 4,2 vs. PI%PC - 31,6 ± 4,3%; p > 0,05). Alta correlação foi observada entre os PI's, tanto para cargas absolutas (r = 0,90; p < 0,01) como relativas (r = 0,83; p < 0,01). Concluiu-se que, apesar de modificações realizadas nos protocolos adotados, foi possível identificar o LL em LP na amostra estudada, em que as intensidades relativas e absolutas a esses limiares não diferiram e apresentaram correlação entre si. Sugere-se a identificação do LL em exercício resistido através de protocolo com incrementos relativos ao PC, tendo em vista a vantagem de não ser necessário submeter o avaliado à aplicação prévia de um teste de carga máxima.

The use of instability to train the core musculature

Training of the trunk or core muscles for enhanced health, rehabilitation, and athletic performance has received renewed emphasis. Instability resistance exercises have become a popular means of training the core and improving balance. Whether instability resistance training is as, more, or less effective than traditional ground-based resistance training is not fully resolved. The purpose of this review is to address the effectiveness of instability resistance training for athletic, nonathletic, and rehabilitation conditioning. The anatomical core is defined as the axial skeleton and all soft tissues with a proximal attachment on the axial skeleton. Spinal stability is an interaction of passive and active muscle and neural subsystems. Training programs must prepare athletes for a wide variety of postures and external forces, and should include exercises with a destabilizing component. While unstable devices have been shown to be effective in decreasing the incidence of low back pain and increasing the sensory efficiency of soft tissues, they are not recommended as the primary exercises for hypertrophy, absolute strength, or power, especially in trained athletes. For athletes, ground-based free-weight exercises with moderate levels of instability should form the foundation of exercises to train the core musculature. Instability resistance exercises can play an important role in periodization and rehabilitation, and as alternative exercises for the recreationally active individual with less interest or access to ground-based free-weight exercises. Based on the relatively high proportion of type I fibers, the core musculature might respond well to multiple sets with high repetitions (e.g., >15 per set); however, a particular sport may necessitate fewer repetitions.

Determination of the lactate threshold and maximal blood lactate steady state intensity in aged rats

The reliability of the lactate threshold (LT) determined in aged rats and its validity to identify an exercise intensity corresponding to the maximal blood lactate steady state (MLSS) were analyzed. Eighteen male aged Wistar rats (approximately 365 days) were submitted to two incremental swimming tests until exhaustion, consisting of an initial load corresponding to 1% of body mass (BM) and increments of 1% BM at each 3-min with blood lactate ([lac]) measurements. The LT was determined by visual inspection (LT(V)) as well by applying a polynomial function on the [lac]/workload ratio (LT(P)) by considering the vertices of the curve. For the MLSS, twelve animals were submitted, on different days, to 3-4 exercise sessions of 30-min with workload corresponding to 4, 5 or 6% BM. The MLSS was considered the highest exercise intensity at which the [lac] variation was not higher than 0.07 mM.min(-1) during the last 20-min. No differences were observed for the test-retest results (4.9 +/- 0.7 and 5.0 +/- 0.8 %BM for LTv; and 6.0 +/- 0.6 and 5.8 +/- 0.6 %BM for LTp) that did not differ from the MLSS (5.4 +/- 0.5 %BM). The LT identified for aged rats in swimming, both by visual inspection and polynomial function, was reliable and did not differ from the MLSS.