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Cardiovascular Health and Exercise

Treadmill Training

Body-weight–supported treadmill training (BWSTT) is an exercise protocol that has been used to potentially affect a number of domains, including motor recovery, bone density, cardiovascular fitness, respiratory function, as well as quality of life. Traditional BWSTT involves the upright walking on a motor-driven treadmill while a harness (suspended from an overhead pulley system) supports the participant’s body weight. Therapists conducting the session determine the magnitude of off-loading of an individual’s body weight (Phillips et al. 2004). The treadmill velocity, the amount of body weight supported, and time spent on the treadmill can be individualized (Phillips et al. 2004). Significant resources are often required as the majority of individuals will require one or two assistants to manually help ambulate the lower limbs.

For a more extensive consideration of BWSTT, please visit the section on Lower Limb, Balance and Walking chapter.

Author Year; Country
Score
Research Design
Total Sample Size

 Methods Outcomes

Alexeeva et al. 2011; USA
PEDro = 7
RCT
Level 1
N = 35

 Population: 35 SCI patients (30 male, 5 female, >1 year; AIS 16–70 yrs; injury to at or rostral to the T10; able to rise to standing position with moderate assistance or less, and independently advance at least one leg.
Treatment: Patients were randomized to 3 groups (body-weight-supported (BWS) walking on a fixed track vs. BWS walking on a treadmill vs. comprehensive physical therapy). The BWS groups used 30% BWS. Patients participated in a 13 week (1 hr/day, 3 d/wk) program.
Outcome measures: performance values, heart rate, pre- and post-training maximal 10-m walking speed, balance, muscle strength, fitness (VO2peak), and quality of life.
  1. Participants in the BWS walking on a fixed track group achieved the highest average heart rate during training, whereas those in physical therapy had the lowest average heart rate.
  2. In all three groups there was a clinically important post-training increase in average normalized VO2peak (~12% in each group); however, these differences did not achieve statistical significance.

Gorman et al. 2016; USA
RCT
Level 1
PEDro = 6
N=18

Population: 18 individuals chronic motor incomplete spinal cord injury between C4 and L2; >1 y post injury.
Treatment: Participants were randomized to Robotic-Assisted Body-Weight Supported Treadmill Training (RABWSTT) or a home stretching program (HSP) 3 times per week for 3 months. Those in the home stretching group were crossed over to three months of RABWSTT following completion of the initial three month phase.
Outcome Measures:  Peak VO2 was measured during both robotic treadmill walking and arm cycle ergometry: twice at baseline, once at six weeks (mid-training) and twice at three months (post-training). Peak VO2 values were normalized for body mass.
  1. The RABWSTT group improved peak VO2 by 12.3% during robotic treadmill walking (20.2 ± 7.4 to 22.7 ± 7.5 ml/kg/min, P = 0.018)

Peak VO2 during robotic treadmill walking and arm ergometry showed statistically significant differences.
Effect Sizes: Forest plot of standardized mean differences (SMD ± 95%C.I.) as calculated from pre- and post-intervention data

Millar et al. 2009; Canada
PEDro = 6
RCT with crossover
Level 1
N = 7

 Population: 7 SCI participants (6 male, 1 female, mean age 37.1 + 7.7 yrs), with C5-T10 level injury, AIS A-C, 5.0 + 4.4 yrs post-injury
Treatment: Each participant underwent both body-weight supported treadmill training (BWSTT) and head-up tilt training (HUTT) in random order, for 3 times a week for 4 weeks, separated by a 4 week detraining period.
Outcome Measures: Heart rate variability; heart rate complexity (what does this capture?); fractal scaling distance score (the correlation of the time between heart beats).
  1. No significant difference in heart rate variability after either BWSTT or HUTT training.
  2. There was increased sample heart rate complexity after BWSTT, whereas HUTT had no effect.
  3. BWSTT, but not HUTT, reduced the fractal scaling distance score in participants.

Fenuta et al. 2014; Canada
Prospective Controlled Trial
Level 2
N= 14

 Population: 7 males with incomplete spinal cord injury; mean age= 42.6 ± 4.29y; years post injury= 4.0 ± 0.62y; 7 able bodied males; mean age= 42.7 ± 5.40y;
Treatment: Steady-state locomotion using the same bodyweight support (BWS) percent was compared in 7 males with incomplete SCI and matched noninjured controls using the Lokomat, Manual Treadmill, and ZeroG.
Participants completed walking trials in a randomized order using the Andago GmbH treadmill system or overground ZeroG. EMG electrodes were placed on tibialis anterior, rectus femoris, biceps femoris, and medial gastrocnemius muscles of both legs.
Outcome Measures: Peak VO2 testing, Heartrate (HR), Lower limb EMG,
  1. A strong positive correlation () was found between the flexion: extension strength ratio at the hip in participants with SCI and the amount of BWS required to complete the overground walking session; the higher the flexion: extension ratio, the more support that was required.
  2. Lokomat sessions resulted in significantly lower MET values when compared to the Manual Treadmill or ZeroG sessions.
  3. For individuals with SCI, average muscle activation tended to be higher for both treadmill conditions compared to the ZeroG session, which could be attributed to increases in TA and BF activity.

de Carvalho et al. 2006; Brazil
Prospective Controlled Trial
Level 2
N = 21

 Population: 21 male participants (C4 to C8), all complete with tetraplegia, mean age 32 ± 8 yrs. 11 assigned to the gait group and 10 controls.
Treatment: BWST training (30%–50%) with neuromuscular electrical stimulation 20 min/day, 2 days/week for 6 months. Control group performed conventional physiotherapy.
Outcome Measures: blood pressure, oxygen uptake, carbon dioxide production, minute ventilation (volume of gas entering lungs), and heart rate.
  1. Gait training (six months) resulted in significant increases in oxygen consumption (36%), minute ventilation (31%), and systolic blood pressure (5%) during the gait phase. In the control group, there were significant increases in resting oxygen consumption and carbon dioxide production (31 and 16%, respectively).
  2. Gait training resulted in an increased aerobic capacity due to yielding higher metabolic and cardiovascular stress.

Jeffries et al. 2015; USA
Cohort Study
Level 2
N=8

 Population: 8 non-ambulatory individuals with chronic motor complete SCI (7 males, 1 female, T5-T12) and 8 healthy able-bodied (AB) controls.
Treatment: SCI group- Standing and stepping exercises over a treadmill in a body weight support (BWS) system with manual assistance of lower body kinematics. Weight support was provided by an overhead lift at high (>50% BWS) or low levels (20-35% BWS). AB participants did normal stepping over a treadmill and standing.
Outcome measures: Oxygen Consumption (VO2) and heart rate during stepping and standing with BWS. VO2 and heart rate responses were assessed in relation to level of BWS.
  1. Significant main effect of task on VO2 for SCI and AB groups. There was a significant increase in VO2 with stepping compared with sitting and standing. There was also a significant increase in VO2 when weight support was decreased during stepping.
  2. Significant main effect of task on heart rate levels for both SCI and AB groups. There was a significant increase in heart rate with stepping compared with seated and standing.
  3. The SCI group also had significant increases in heart rate from seated to standing
  4. No difference in heart rate when weight support was decreased during stepping for both groups.

Stevens and Morgan, 2015; USA
Pre-post
Level 4
N=11

 Population: 11 adults with incomplete SCI (7 males, 4 females, mean age 48). 6 adults with injuries at or above T5 and 5 adults with injury below T5.
Treatment: 8 weeks of Underwater Treadmill Training (UTT) (3 sessions per week, 3 walking trials per session) incorporating individually determined walking speeds, personalized levels of body weight unloading, and gradual, alternating increases in speed and duration. In weeks 2,4,6, and 8, walking speed was increased by 10%, 20%, 30% and 40% over baseline.
Outcome Measures: Heart rate
  1. None of the interaction tests involving injury level were statistically significant. When averaged over injury level, the interaction between training period and day was significant.
  2. Pairwise comparisons revealed that from day 1 to day 6, heart rate fell by 7%, 14% and 17% during training periods 1, 2, 3. All participants exhibited significant decreases in daily submaximal exercise (walking) heart rate for each 2-week period.

Turiel et al. 2011; Italy
Pre-post
Level 4
N = 14

 Population: 14 participants (10 males, 4 females; mean age 50.6 ± 17.1 yrs; 2-10 yrs post-injury; 9 paraplegia) with lost sensorimotor function caused by incomplete SCI.
Treatment: BWSTT assisted with robotic driven gait orthosis for 60 min sessions, 5 d/wk, 6 wk, with 30-50% of body weight supported (reduced as tolerated).
Outcome Measures: Left ventricular function, coronary blood flow reserve (via dipyrsidamole stress echo), plasma asymmetric dimethylarginine (ADMA) (marker of vascular abnormalities observed in cardiovascular disease and ageing), and plasma inflammatory markers.
  1. Significant improvement in the left ventricular diastolic function (i.e., a reduction in isovolumic relaxation time and deceleration time was observed following the training.
  2. Significant Increase in coronary reserve flow and reduced plasma ADMA levels was observed in the follow-up.
  3. Significant reduction in the inflammatory status (C-reactive protein and erythrocyte sedimentation rate).

Jack et al. 2009; UK
Pre-post
Level 4
N = 2

 Population: Participant A: female, T9 level injury, age 41 yrs, 2 yrs post-injury; Participant B; male, T6 level injury, age 40, 14.5 yrs post-injury
Treatment: Body-weight supported treadmill training (BWSTT), three 30-min sessions per week for 16 weeks (participant A) or 20 weeks (participant B)
Outcome Measures: Measures of cardiopulmonary fitness: oxygen uptake (VO2); peak heart rate; dynamic O2 cost
  1. Both participants’ VO2 increased after exercise, 8.2 to 10.2 mL∙kg-1∙min-1 for participant A; for participant  B, VO2 increased from 13.8 to 18.2 mL∙kg-1∙min-1 at week 17, after which the VO2 dropped back to 13.9 mL∙kg-1∙min-1.
  2. Peak heart rate increased for both participants after exercise (89 to 119 BMP for participant A, 134 to 157 bpm for participant B).
  3. The dynamic O2 cost decreased for both participants (115 to 29.03 mL∙min−1∙W−1 for participant  A, 66.57 to 4.52 mL∙min−1∙W−1 for participant  B).

Soyupek et al. 2009; Turkey
Pre-Post
Level 4
N = 8

 Population: 8 incomplete SCI participants, 6 male and 2 female, injury level C6-L1, mean age 40. 8 +13.9 yrs (range 26-66 yrs)
Treatment:  Body weight supported treadmill training (BWSTT), for 5 times per week for 6 weeks; length of training sessions ranged from 10 to 30 min
Outcome Measures: Heart rate and blood pressure; Forced expiratory volume in 1 second (FEV1), forced vital capacity (maximum amount of air that can be expelled after maximum inhalation), inspiratory capacity, maximum inspiratory and expiratory pressure
  1. The heart rate was significantly lower post-training compared to baseline
  2. There were significant improvements of the forced vital capacity and inspiratory capacity in participants post-training compared to baseline
  3. There were no significant difference in other parameters between pre-and post-training

de Carvalho and Cliquet 2005; Brazil
Pre-post
Level 4
N = 12

 Population: 12 male participants (C4 tp C7) all complete with tetraplegia; Mean age = 33.8 y; Median time post-injury = 77.58 months
Treatment: Body weight supported treadmill training (30–50%) with neuromuscular electrical stimulation 20 min/day, 2 days/week for 3 months.
Outcome Measures: BP and HR.
  1. After training, mean systolic blood pressure increased (94 ± 5 mmHg to 100 ± 9 mmHg) at rest and during gait exercise (105 ± 5 to 110 mmHg).
  2. There were no significant changes in post-exercise blood pressure after training.

Ditor et al. 2005a; Canada
Pre-post
Level 4
N = 8

 Population: 8 participants (6 males, 2 females), AIS  B-C, C4-C5, incomplete, mean age 27.6 yrs, mean 9.6 yrs post-injury.
Treatment: Progressive, body weight-supported treadmill training, 3 day/week for 6 months.
Outcome Measures: HR and BP variability, LF/HF ratio (low to high heart beat frequency and is indicative of balanced sympathetic/parasympathetic tone and reduced risk for cardiovascular-related mortality).
  1. Significant decrease in resting HR (10.0%) after training.
  2. No changes in resting systolic, diastolic, or mean arterial BP after training.
  3. Significant reduction in the resting LF/HF ratio after training.
  4. There were no significant effects of training on HR and/or blood pressure variability during an orthostatic challenge (60° head up tilt).

Ditor et al. 2005b; Canada
Pre-post
Level 4
N = 6

 Population: 6 participants (4 male, 2 female), AIS  A and B, C4-T12, mean age 37.7 yrs, mean 6.7 yrs post-injury, motor complete.
Treatment: Body weight supported treadmill training, 15 min/day (3 bouts of 5 min), 3 days/week for 4 months.
Outcome Measures: BP, HR, HR variability, BP variability, arterial diameters and mean blood velocities, and arterial blood flow.
  1. No changes in femoral or carotid artery cross-sectional area, blood flow, or resistance post-training
  2. An improvement in femoral artery compliance.
  3. No change in resting BP, mean arterial blood pressure, resting HR or heart rate and blood pressure variability after training.
  4. 3/6 patients had changes in heart rate and blood pressure variability reflective of increased vagal predominance.

Discussion

There are two randomized controlled trials (Level 1a) (Millar et al. 2009; Alexeeva et al. 2011), and one prospective controlled investigation (Level 2) (de Carvalho et al. 2006) and several pre-post studies (Level 4) have been conducted to examine changes in indicators of cardiovascular fitness/health in SCI after training (de Carvalho & Cliquet, 2005a; Ditor et al. 2005a; Ditor et al. 2005b; Jack et al. 2009; Soyupek et al. 2009; Turiel et al. 2011).

Four recent investigations examined the effects of BWSTT (Jeffries et al. 2015; Alexeeva et al. 2011; Turiel et al. 2011) and underwater treadmill training (Stevens and Morgan 2015) on indicators of cardiovascular fitness and/or health. Alexeeva et al. (2011) compared participants randomly assigned to two different BWS ambulation modalities in comparison to traditional physical therapy, and revealed that there were clinically important improvements in normalized VO2 peak in each group. Turiel et al. (2011) demonstrated that 6 weeks of BWSTT resulted in improvements in resting left ventricular function, coronary blood flow reserve and inflammatory status.

In 2009, Jack et al. examined two participants (with thoracic injuries) after BWSTT and revealed significant improvements in peak heart rate (HR) and oxygen consumption (VO2), and a decrease in the dynamic oxygen cost (the rate of oxygen consumption by respiratory muscles as they ventilate the lungs). Soyupek et al. (2009) evaluated 8 subjects and found significantly lower heart rate post-training and improved forced vital capacity (maximum amount of air that can be expelled after maximal inhalation) and inspiratory capacity.

Stevens and Morgan (2015) examined the effects of 8 weeks of progressive and individualized underwater treadmill training (3 days per week, 3 walking trials per session). They revealed evidence of improved cardiovascular control and function (i.e., reduced submaximal HR) across the training intervention.

The two earlier studies were conducted by the same Canadian research group (Ditor et al. 2005a; Ditor et al. 2005b). They reported that BWSTT did not have substantial group effects on HR and blood pressure in motor-complete subjects but did reveal a significant reduction in resting HR in the study that involved individuals with incomplete tetraplegia. There was also evidence that improvements in HR and blood pressure variability may occur after BWSTT in incomplete SCI and a subset of participants with complete SCI. The authors attributed the change in blood pressure variability to reductions in sympathetic tone to the vasculature. These findings have significant physiological relevance since it indicates that both parasympathetic outflow to the heart (as evaluated by heart rate variability) and sympathetic flow to the vasculature (as evaluated by blood pressure variability) can adapt in response to exercise training. This research group also revealed the potential for improvements in vascular health (e.g. arterial compliance) after BWSTT in individuals with motor-complete SCI. There was no indication of the effects of BWSTT on peak oxygen consumption (VO2peak).

The mechanisms responsible for the improvement in markers of cardiovascular health and regulation in individuals with incomplete SCI remain to be determined. Jack et al. (2009) postulated that an improvement in walking ability likely explained the increase in VO2peak with training (in individuals with incomplete SCI). They also highlighted how marked atrophy, fast fatiguing lower limbs and limited neural control may limit the capacity of patients with SCI to make use of their cardiovascular reserve.

Ditor et al. (2005a,b) attributed the training-induced changes in autonomic function to the cardiovascular challenge provided by the upright nature of BSWTT (which potentially could be a sufficient stimulus in individuals with postural hypotension) and the spasticity created during the treadmill training. However, it should also be noted that both weight bearing and the passive movement of the limbs may contribute to the observed changes in these studies.

A recent Canadian study employing a randomized cross-over design (Millar et al. 2009) revealed that short-term (4 weeks) BWSTT (but not head-up tilt training) led to a significant increase in HR complexity and reduced fractal scaling distance score in persons with SCI. These changes are thought to reflect an improvement in cardiac autonomic balance after short-term BWSTT.

Two investigations (a pre-post study (level 4) and a prospective controlled study (level 2) from the same research group used partial BWSTT (30%–50%) via neuromuscular electrical stimulation assisted by physiotherapists (de Carvalho & Cliquet 2005a; de Carvalho et al. 2006). The first investigation revealed that three months of this form of gait training can result in a significant increase in systolic blood pressure at rest and during gait exercise in males with tetraplegia (de Carvalho & Cliquet 2005b). In the latter study (de Carvalho et al. 2006) the authors revealed that long-term neuromuscular electrical stimulation gait training (six months) resulted in significant increases in VO2 (36%), minute ventilation (30.5%), and systolic blood pressure (4.8%) during the gait phase. The authors concluded that treadmill gait training combined with neuromuscular electrical stimulation leads to increased metabolic and cardiorespiratory responses in persons with complete tetraplegia.

In a comparison of trials using BWSTT, an interesting discrepancy arises. For instance, in the work of Ditor et al. there was no change in resting blood pressure after BWSTT in individuals with complete or incomplete SCI (Ditor et al. 2005a; Ditor et al. 2005b). Whereas, the work by de Carvalho and coworkers revealed an increase in resting blood pressure following partial BWSTT (with neuromuscular electrical stimulation) (de Carvalho & Cliquet 2005b; de Carvalho et al. 2006). It is not clear why these discrepancies exist, and, as such, further research is clearly warranted.

It is important to note that while BWSTT may have important cardiovascular benefits, the feasibility of using this treatment over the long term in the home setting is questionable due to the costs of the equipment and assistants to set up the individual and facilitate the leg motions.

Conclusion

There is level 1a evidence (Millar et al. 2009) that BWSTT improves cardiac autonomic balance in persons with tetraplegia and paraplegia (with similar results for varying degrees of lesion level and severity).

There is multiple level 4 evidence (Jack et al. 2009; Soyupek et al. 2009) that BWSTT increases peak oxygen uptake and heart rate, and decreases the dynamic oxygen cost for persons with SCI.

There is Level 2 evidence (Jeffries et al. 2015) that indicates that standing and stepping exercises with BWSTT can increase VO2 and heart rate levels.

There is Level 4 evidence (Ditor et al. 2005b) that indicates that BWSTT can improve arterial compliance in individuals with motor-complete SCI.

There is Level 4 evidence (Stevens & Morgan 2015) that 8 weeks of underwater treadmill training decreases walking exercise heart rate.

There is level 2 evidence (de Carvalho et al. 2006) that neuromuscular electrical stimulation gait training can increase metabolic and cardiorespiratory responses in persons with complete tetraplegia.

There is growing evidence that BWSTT can improve indicators of cardiovascular health in individuals with complete and incomplete tetraplegia and paraplegia.

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